EFFECT OF SCME ENVIRONMENTAL FACTORS UPON DEVELOPMENT
OF IMMATURE STAGES OF AEDES AEGYPTI (LINNAEUS)
DISSERTATION
Presented in Partial Fulfillment of the Requirements
for the Degree Doctor of Philosophy in the
Graduate School of The Ohio State University
By
JULIUSjRUDINSKY, Forestry Engr.
The Onio State University
1953
Approved by:
i
TABLE OF CONTENTS
Page
Introduction-------------------------
1
The Effects of Constant Temperatures upon Development
of Aedes aegypti Immature Stages---------
U
Introductory Consideration - Historical Review
----- -- ----- - -
-
---- - - - - - - - - - - - - - - ----
Experimental Methods
-
- -
5>
11
20
Constant Temperature Effect on Immature Stages -------First Instar - - - - - - - -
- - - - - - -
22
23
_ _ _ _ _ _ _ ---------
26
Third Instar - - - - - - - - - - - - - - - -
27
Fourth Instar
- - - - - - - - - - - - - - -
29
Pupal Stage
---
30
-
Second I n s t a r
From Hatching to Emergence - - - - - - - - -
31
3k
Comparative Discussion----------------------The Relation of Temperature to Survival of Imma­
ture Stages. The Threshold, Low and
High Lethal Temperatures, Optimal
-------_ _ _ _ -----Survival
38
The Relation of Surface-Volume Ratio to the Development
of Aedes aegypti larvae --- - - - - - -- - - - - - Introductory Remarks and Methods
h3
---
Results of Surface-Volume Ratio Investigation
U2
- ------
U5
Quantitative and Qualitative Examination of the
Microflora Found in the Water used for
Rearing Aedes aegypti larvae ----------------
U9
Discussion
- -
A 0C136
51
ii
Page
The Effects of Different Wave Lengths of Light upon the
Development of Aedes aegypti Immature Stages - Introductory Considerations
Historical Review
- - - - - -
-----
-
5U
- --- - -
55
-
61
Experimental Methods - - - - - - - - - - - - - - - - -
68
Relation of Light of Different Wave Lengths to
Development of Immature Stages
-------
72
Relation of Fluorescent Light to the
Velocity of Development and
Emergence Density of Aedes
aegypti-------
72
Relation of Infrared Light to the
Velocity of Development and
Emergence Density of Aedes
aeggpti--------------------------
73
Relation of Intensity of Ultraviolet
Light to the Velocity of
Development and Emergence
Densityof Aedes aegypti--------
76
Comparative Discussion----
----
79
Infrared Light - - - - - - - Fluorescent L i g h t
Ultraviolet Light
--------- - - - - -
S u m m a r y ------Bibliography-------
-- _ _ _ _ _
-- _ _ _ --
79
82
83
87
-
90
iii
LIST OF FIGURES
Page
Fig.
Fig.
Fig.
Fig,
Fig.
Fig.
Fig.
1
2
3
U
5
6
7
Developmental Reaction of the First and Second
Instars of Aedes aegypti under Constant
Temperatures------Developmental Reaction of the Third and Fourth
Instars of Aedes aegypti under Constant
Temperatures - - - - -- -- - - - - -
Fig.
8
9
- - -
28
Developmental Reaction of the Pupal Stage and
the Combined Immature Stages of Aedes
aegypti under Constant Temperatures ------
32
Developmental Velocity Relationship to Mortality
of Immature Stages of Aedes aegypti under
Constant Temperatures
___
ho
Set of Jars with Different Surface Area Used
in the Experiments of Surface-Volume Ratio
hh
Developmental Velocity, pH of Water, Weight of
Pupae - in Relation to the Surface Area
--- - -
U8
Upper:
Partial View of Controlled Temperature
Cabinet with Containers Exposed to Differ­
ent Intensities of Fluorescent Light,
Showing Covers Made from Onionskin Paper - - - Lower:
Fig.
25
Total View of the Same Set-up - - - - - - - -
Upper:
Relationship of Time of Development
(in Hours) to the Different Intensities of
Fluorescent, Infrared and Ultraviolet Light
69
--
Lower: Developmental Velocity Relationship to
Different Light Intensities of Fluorescent
(FL), Infrared (IR), and Ultraviolet (UV)
L i g h t ---------------------------------------
7h
Spectrophotograph of Infrared (IR), Fluorescent
(FL), and Ultraviolet (UV) Light from
Sources Used in Experiments
-----------
86
iv
The author wishes to express his appreciation to the Research
Foundation,
The Ohio State University, and The National Institutes
of Health for being given the opportunity to perform the present work;
to Dr. D. M. DeLong for valuable advice and help during the investiga­
tion;
ments;
to Dr. S. S. Ristich for many suggestions in conducting experi­
to Dr.
R. Edse,
nautical Engineeringj
Assistant Professor - Department of Aero­
and Mr. G. G. Sumner, Department of Chemistry,
for their advice in radiation and hydrogen-ion concentration;
to
Mr. J. Sudimack, Department of Bacteriology, for performing the quan­
titative and qualitative analysis of microflora;
Ludwig for assistance in laboratory problems.
and to Mr. P. D.
EFFECT OF SOME ENVIRONMENTAL FACTORS UPON DEVELOPMENT
OF IMMATURE STAGES OF AEDES AEGYPTI (LINNAEUS)
INTRODUCTION
The environments of different insects vary to a great extent, but
there are some environmental factors to which all insects, terrestrial
and aquatic, are exposed.
These are temperature, humidity and other
habitat conditions which we may classify as almost entirely meteorolog­
ical.
These meteorological conditions, however, affect not only in­
sects which are exposed to the direct action of the atmosphere but also
insects not directly exposed to it, since temperature, humidity, etc.
conditions are dependent on the intensity of the solar radiation, on
the amount of precipitation, humidity and evaporation of the air, in­
deed, on the whole complex of phenomena expressed by the word "climate"
which is the ever present factor in insect life.
All other environ­
mental conditions are subordinate to it in importance, even if their
relative values are not the same throughout the life cycle of an insect
The existence of an insect, of course, depends to a great extent on
conditions other than climatic, but climate still remains as a definite
factor in the life of insects.
Climate, as Uvarov (1931) expressed it,
is an extremely intricate complex of phenomena, and it seems useless to
attempt to study its influence on insect life by methods other than an­
alytical .
The writer was given the opportunity to investigate some of the
basic climatic relationships of insects when he was appointed as
- 2 -
Research Fellow on the research project sponsored by the Ohio State
University Research Foundation and the National Institutes of Health.
The work on this project is devoted to basic research on two types of
mosquitoes which are very important from the health standpoint, namely
the malaria mosquito, Anopheles quadrimaculatus Say, and the yellow
fever mosquito, Aedes aegypti (Linnaeus).
After a preliminary survey
of the literature on the ecological factors in the development of im­
mature stages of these mosquitoes the attention of the writer was
directed to the lack of informative material on Aedes aegypti parti­
cularly.
Therefore, this mosquito was chosen as the experimental in­
sect for the present studies.
The work was directed toward three major aspects of the environ­
mental complex.
The first of these is the time-temperature relation­
ship of the thermally unspecified insect species.
The experimental
methods used were applied to each of the successive immature stages
with the eventual establishment of the differences and similarities be­
tween them as to optimal developmental temperature, optimal survival
temperature, threshold, and low and high lethal temperatures.
For the
expression of this time-temperature relationship the caternary expon­
ential formula was found most applicable.
Tie second relationship study was that of the surface-volume ratio
and its effect upon time of development and subsequent changes in the
water media.
The effect of radiation of different wave lengths upon the devel­
opment of the immature stages of this mosquito was the third aspect to
be investigated.
Three ranges of radiations which- were applied were
infrared, visible and ultraviolet.
As a result of their application the
- 3 -
most effective intensities were established.
1
¥
5
4
It is believed that these results may be of assistance in practical
control work of this species and also in future research on its basic
environmental relationships.
j
-li­
ras
EFFECTS OF CONSTANT TEMPERATURES UPON
DEVELOPMENT OF AEDES AEGYPTI DOIATURES STAGES
- * -
INTRODUCTORY CONSIDERATION
Before considering the effect of temperature upon the development
of insects it seems to be necessary to define the meaning of the term
"development".
Janisch (1930) proposed considering that the full
period of development of an organism is the amount of time which an
organism needs to pass from the beginning of embryonic development to
the physiological death which results from old age.
Considering devel­
opment from this point of view, the development would include not only
formation of the embryo, growth of larva and larval tissues, the pupa,
the sexual development of the adult, but the processes of senescence as
well.
Most biologists, however, consider senescence not as a continua­
tion of development but rather as an opposite process.
Therefore,
development is usually defined as the process of building up an organism
terminating with sexual maturity.
At a certain point of low temperature all insects become inactive
which indicates that development is possible only at the temperatures
above a certain point.
This theoretical point has been given several
names by different authors.
The term most acceptable to the biologists
of today for this point of temperature is "threshold of development" or
"minimum effective temperature" which is defined by Peairs (1927) as
the temperature at which, on the descending scale, the development def­
initely ceases, and at which, on the ascending scale, the development
is initiated.
According to this definition it should be possible to
keep an insect at this temperature for an indefinite period without any
changes.
This is, of course, only a theoretical possibility since it
is clear that long exposures even to moderately low temperatures may be
- 6 -
fatal.
It is very difficult to determine the exact threshold of devel­
opment for a given stage of an insect because of the very small amount
of development ■which is talcing place at a very slow rate.
Most biol­
ogists tried to overcome this difficulty by accepting as the theoretical
threshold the point at which the reciprocal curve of development inter­
sects the temperature axis.
Peairs (1927) and Shelford (1929) have
proved that this is only an approximation.
Von Oettingen (1879) and later Shelford (1929) tried to calculate
the approximate threshold of development by series of observations
made on the length of developmental period at different constant temp­
eratures.
Then several probable values for the threshold were assumed,
and the temperatures above the threshold were multiplied by the time.
The most constant value within the widest range of temperature was
chosen as correct.
The old concept that a temperature of 6.1° C. is the
beginning of development generally has been proven to be incorrect, be­
cause not only different insects but even different stages of the same
insect have different thresholds.
The actual threshold could be found
only by observing the development of an insect stage at several low
temperatures.
In this manner Sanderson (1910) found that the threshold
for the grain aphis, Toxoptera graminum Rond., is 1.6^° C., while that
for the egg and larva of the codling moth isabout 10° C., and
pupa 11,1° C.
According to Shelford (1927)
for the
thethreshold varies, with­
in certain limits, with humidity and other factors, as well as with the
generation and the Individual.
According to
him the threshold for lar­
vae of the codling moth varies from 6.1° to 8 .8° C. for pupae, for the
hibernating larvae from 6.1° to 10° C. and for the eggs from 6.7° to
9.h° C.
- 7 -
"Developmental zero" or "physiological zero" are other terms which
have been commonly used to indicate the point of low temperature at
which insects become inactive.
They are, however, not very acceptable
because they imply that there is no metabolism going on which is obvious­
ly incorrect.
Below the minimum effective temperature, life continues in a temp­
erature zone of dormancy below which there is the lower fatal limit.
The lower fatal limit was studied in a number of insects by various in­
vestigators
(Uvarov, 1931)> but there is not much uniformity with re­
gard to the lovrer fatal limit of temperature in insects.
Certain
species may be killed by temperatures hardly below the freezing point
while others survive exposure to extremely low temperatures.
Bach-
metjew (1901) made rather extensive experimentations and summarized the
early literature on the subject.
According to him the insect may be
cooled below the freezing point without being injured and may exist in
an undercooled condition.
"When it does freeze, the heat of crystalliza­
tion will be equal to the undercooling temperature, and the body temp­
erature will rebound to the freezing point.
Cooling will again proceed,
and, when the insect reaches the undercooling point the second time, ac­
cording to Bachmetjew's conception, death follows.
Payne (1926) got
evidence that certain insects which are normally exposed to extremes of
temperature undergo a hardening during the fall of the year during which
time their freezing points are depressed and their ability to endure
cold is increased.
In spring the reverse of this process occurs, and
the highest percentage of larvae are killed when cold spells are exper­
ienced after the freezing point and endurance of low temperature has
been altered.
- 8 -
Tropical insects which are not normally exposed to extremely low
temperatures are unable to endure dormancy according to Chapman (1931).
In general, insects of temperate regions which hibernate in exposed
situations are able to endure freezing and survive.
Our present knowledge of the "upper temperature limit of develop­
ment" is very unsatisfactory.
As a matter of fact, it is doubtful
whether this point is distinct from the upper fatal limit, because, if
there existed an appreciable interval between the upper limit of devel­
opment and the upper fatal point, we should be able to observe a quies­
cent state of developing in an insect at that range similar to that at
the temperatures between the threshold of development and the lower
fatal limit.
The upper fatal limit, contrary to the lower fatal limit, is fairly
uniform for various insects and lies on the average at about U8° C. to
52° C.
Several authors have pointed out that there may be considerable
individual variation in the resistance to high temperatures in individ­
uals of the same species.
Such individual variations in the resistance
to the upper fatal limit are of considerable importance for the survival
of the species during abnormally high temperatures.
An exposure to a
high temperature may very often have no apparent immediate effect upon
an insect.
The subsequent development, however, and the duration of
life are often very seriously affected even by short exposures.
Baum-
berger (19lLi) has conducted numerous experiments and has published a
table showing the length of adult life of various insects at different
temperatures.
He reached the conclusion that the increase in the length
of the adult life is approximately proportional to the temperature in
the same order as required by van't Hoff's rule for the chemical re­
- 9 -
actions.
Bachmetjew (1907) drew attention to the importance of the
water content of the insect's body and suggested that insects contain­
ing more water would die at a given high temperature more quickly than
insects with less water.
The combined action of temperature and humid­
ity is an important factor affecting the resistance to heat.
Consider­
ing the fatal action of the lower fatal limit and the fatal action of
the upper fatal limit upon an insect organism it is clear that there
exists a great difference;
both produce stupor at first, but, while an
insect which is frozen so as to become hard may be revived by raising
the temperature, the stupor produced by heat is invariably fatal, pro­
vided the exposure is sufficiently long.
In other words, the action of
heat is irreversible (Matisse, 1919).
Between the limits of minimum effective and maximum effective
temperatures (or threshold and upper temperature limit of development)
there is a zone in which poikilothermic organisms are active.
Somewhere
within this zone there is a place which may be called the optimal temp­
erature, where life is at an optimum, not necessarily with respect to
rates of development but at which conditj ons are generally most favor­
able for the organism.
"Optimal temperature" or "developmentally optimal temperature" is
considered by Uvarov (1931) as that range at which the rate of develop­
ment is the highest.
This tenqperature, however, occurs near the upper
limit, is accompanied by a fairly high percentage of mortality and may
bear no rigid correlation with the optimal temperature for maximal
biotic potential.
Blunck (191U) and Peairs (1927) define the optimal
temperature as that temperature at which the relatively greatest per­
centage of individuals accomplish their development within the rela-
- 10 -
tively shortest period of time.
In this way Blunck (191b) determined
the optimal temperature for the eggs of Dytiscus marginalis L. as 10° 15° C., while the threshold of development is 0° C. and the upper limit
about 30° C.
Janisch (1930) considers the optimum temperature as a point in
the temperature scale - not a zone - in his asymmetrical caternary
curve which represents the duration of life as affected by temperature.
The lowest point of his curve corresponds to the optimum temperature at
which the insect develops most rapidly and reaches its physiological
death within the shortest time.
Agrell (19U7) considers the temperature
as optimal at which the oxygen intake is smallest.
"Optimal temperature" in the present work is used as the temperature
at which the rate of development is highest.
is a developmentally optimal temperature only.
This temperature, however,
- 11 -
HISTORICAL REVIEW
Up to the present day there is no general way of expressing by
mathematical means the reaction of poikilothermic organisms to temp­
erature changes (due to the complexity of biological processes).
Be­
fore analyzing the present experiments it seems to be necessary to con­
sider the relation of constant temperature to the metabolism of these
organisms.
This, however, would be impossible without reference to
the nature of the effects of temperature on the chemical and physical
processes of the structure of an organism.
It is hardly necessary to state that temperature has a profound
effect upon all physical and chemical processes;
our concept of temperature is based upon them.
as a matter of fact,
Radiation, gelation,
diffusion, surface tension, imbibition, crystallization and viscosity
are only some of the more important phenomena which are greatly af­
fected by temperature, including all chemical reactions.
Remembering
that temperature affects each process to a more or less different de­
gree and that changes of varying kind and degree may take place in an
organism at the same or a different time, it is easy to understand that
we are not able to explain fully the effects of temperature in ecology,
physiology or other related fields.
Van't Hoff (188U) made a statement of the general principle of the
effect of temperature on chemical reactions and proposed a new equation
which expressed mathematically his statement (that):
"When the temper­
ature rises 10° C., the velocity of most chemical processes increases
two to three times."
- 12 -
QlO
=
Kt +10
g-
= 2 to 3
He then expressed this logarithmically in such a -way as to take care of
any other difference than 10° C., and reduced it all to a 10° basis.
A
considerable number of attempts have been made by biologists to apply
the rule to the relationship between the temperature and the velocity
of development.
However, the calculation of Q-j_q showed that only in a
few cases and within a limited range of temperatures did the coefficient
approach the value 2 to 3 and that it may vary from as low as 1.2 to as
high as 7.1 since the Q-^q value varies at different temperatures.
The
curve expressing the relationship would be an exponential one, its re­
ciprocal being sigmoid and not straight as in the case of a hyperbola.
Arrhenius (1889) proposed a formal expression of this same rela­
tionship based upon the absolute temperature scale by introducing a socalled critical thermal increment or constant
q .
The function of
this constant is to bring Q^q more closely to a value of 2.
He wrote
the expression:
q
t2 - tj
d2 = °le 7 * t2 •
where D2 is the velocity at higher temperature t2 , %
the reaction at the lower temperature t^ ,
logarithms and
q
e
the velocity of
is the base of natural
is the critical thermal increment.
The value of
q
for most biological processes ordinarily lies between 12,000 and 16.000
and in chemical reactions varies from U.000 to 35.000.
Arrhenius, how­
ever, stated that there is not an essential difference
between the pro♦
cesses studied in chemistry and those produced by living organisms as
- 13 -
measured by the values for
q
. Proponents of the theory contend that
chemical reactions may be compound reactions where, during one portion
of the reaction, one of the components may play a dominant role, while
in another portion, a quite different element will be more essential
with the result that the curve of velocities would not be a simple
curve, but a compound one.
Therefore, different portions of it would
have to be considered differently, and, consequently, the value for
q
in Arrhenius’ equation would have to be changed according to the domin­
ating component at any particular time.
According to Belehradek (1935)
the law of Arrhenius seems to hold good for chemical processes with more
accuracy than the
rule.
Over the narrow range of temperature, how­
ever, at which the living organisms exist the reciprocal of the abso­
lute temperature is practically a linear function of the ordinary temp­
erature so that in biology there is no practical difference between
q
and Qio .
The most familiar theory with regard to the relation between temp­
erature and the rate of development of insects is that of the thermal
constant, suggested by Reaumur (1736) and quantitatively expressed by
Boussingault (1891) according to Belehradek (1930).
By this theory the
completion of a given stage in development requires an accumulation of
a definite amount of heat energy.
Although theoretically good, in
actual work it proved impossible to measure the amount of heat energy.
A method of summing up temperatures during the day - effective daydegrees - was adopted;
i.e. temperatures sufficiently high for devel­
opment, temperatures above the threshold.
Sanderson (1910), Peairs
(1927) and Blunck (1923) after extensive experiments with various in­
sects at different constant temperatures found a mathematical expression
- 11* -
for the correlation between the time of development and heat which
proved to be a true equilateral hyperbola:
(T - K) D » C
where
old,
T
D
is the temperature during the experiment,
K
is the thresh­
is the duration of the stage at that temperature and
thermal constant.
C
is the
This formula means that the temperature, expressed in
effective degrees, multiplied by the time required, is always a constant.
The length of development is, therefore, inversely proportional to the
temperature.
Hie reciprocal values of the length of development ex­
press the relative velocity of the development and the line based on
these values shows the rate of acceleration of development with the ris­
ing temperature.
Any point on this line (velocity line) is the "devel­
opment index" for the given temperature, that point where the velocity
line crosses the temperature axis is the theoretical threshold of dev­
elopment (K).
Peairs (1927) published results of his experiments which
show that the deviations of the experimentally determined points from
the straight line within the medial range of temperatures are very
slight and, therefore, the hyperbola represents the temperature influ­
ence on the duration and rate of development with a sufficient exacti­
tude.
Prochnow (1907, 1908), Krogh (191U), Triend (1927), Shelford
(1927), Kiselewa (1928) and other later authors have now definitely
proved that there are significant departures from the straight line at
both ends of the biokinetic scale.
According to Shelford (1929) the
thermal constant expression is conforming to the observed facts only in
range of medial temperatures, and the deviation of the velocity curve
near its lower end from the straight line does not permit determining
graphically the point of approximate threshold of development which
'n
-
1$
-
should be, as mentioned before, at the point where the straight line
intersects the temperature axis.
Comparing the hyperbola of the thermal constant theory and van’t
Hoff’s exponential curve one will find that within certain limits they
have a similar course while their reciprocals differ considerably.
The reciprocal of the van’t Hoff’s curve is a sigmoid and does not cor­
respond to the empirical data, particularly on the upper end where it
deviates in such a way as to suggest a relative acceleration of vel­
ocity of development at high temperature, while actually quite the op­
posite takes place.
The reciprocal of the straight line (hyperbola),
however, does not correspond to experimental data on both ends.
Janisch found in his experiments that the results agree best with a
catemary exponential curve.
This curve does not differ considerably
from the mentioned two curves within the medial temperature limits.
The reciprocal of the caternary curve presents deviations at both ends
and corresponds very closely to the experimental data.
The reciprocal
of this caternary curve, plotting velocity of reaction against temper­
ature, has the characteristic S-shaped form of the biological curve.
Though both Q]_q
and
q
have proven inadequate as expressions of
the relation of temperature to biological processes, the caternary
curve has been shown to be a good expression of this relationship by
Cook (1927), Menusan (I93li)and Janisch (1932).
The present effort is
further proof of the utility of the catemary curve in expressing the
relation between temperature and developmental velocity.
Janisch’s catemary formula is derived from the "exponential law"
of that author (192!?) and is:
- 16 -
y =
where
y
equals time,
determined optimum,
a
x
m
| (ax
a~x )
equals time of development at the empirically
is the temperature above or below this optimum,
is an empirically determined constant relative to the slope of the
curve.
The catemary curve is derived by the addition of two simple
exponential curves,
y B max
and
y * ma~x , first representing accel­
eration, second retardation of development.
As Janisch (1927) stated,
"This means biologically that two things working opposingly are added,
a positive function, the acceleration of developmental processes
through rising temperature, and a negative function, the retardation
in the processes of development."
At low temperatures the retardation
is very low and the acceleration high.
The closer to the point of op­
timal temperature the more equal become both the functions.
Above the
optimal temperature point the retardation becomes greater and greater,
while accelerating factors are decreasing in importance until soon no
development takes place.
These factors which retard development are
not suddenly operative after the optimal temperature is passed, but
are present as contributing elements even at very low temperatures and
assume an increasing role in the velocity as the temperature is in­
creased.
Martini (1928) in criticizing this theory admits that the ex­
ponential catemary curve draws special attention to the behavior of
the organism at extreme temperatures but points out, however, that it
is "too theoretical to be of direct use for the understanding of the
relationship between temperature and development."
The idea of a three-dimensional curve representing the velocity of
development is the latest.
Proposed by Matisse (1919) and elaborated
- 17 -
later by Cook (1927) who constructed a model of a three-dimensional
curve for metabolism with two variables involved:
length of exposure.
temperature and the
This idea, although scientifically sound, did not
find much use among biologists because of its impractical application.
Experimental investigations on the effect of heat upon the rate of
development have been conducted in the majority of the experiments with
constant temperatures although it has been known that constant and var­
iable temperatures produce different rates of insect metabolism.
The
American Yellow Fever Commission ifc Cuba (Reed and Carroll, 1911) first
worked out the essential phases of the biology of Aedes aegypti.
The
minimum duration of the early stages of development, as indicated by
Reed and Carroll, was seven and one-half days;
pupal stage 36 hours.
larval stages six days,
It may be assumed, of course, that this was un­
Goeldi (1909)
der natural conditions, with fluctuating temperature.
obtained a minimum of four days for the larval stages.
McGregor (1931)
states that the strain of A. aegypti used at the Wellcome Entomological
Field Laboratory when kept at constant temperature of 30° C. produces
successive generations on the average of every 10 to 19 days throughout
the year.
Shannon and Futnam (193U) state that under the most favor­
able rearing conditions at temperatures of 23° to 27° C. pupation
occurred in from 6 to 7 days with low mortality.
Headlee (19U0, 19U1)
in his experiments upon metabolic power of A. aegypti with constant and
variable temperatures obtained very unusual results.
At 89° F. (29.U°C.)
constant temperature larvae developed into adults in 13.9 days, at 79° F.
(23.9°C.) in 19,7 days, and at 69° F. (18.3°C.) in 2U .2 days.
Chapman (1931) and Imms (1937) reviewed the literature on the ef­
fect of constant and variable temperature upon rate of development and
- 18 -
stated that the data were not conclusive as to whether the exposure to
variable temperatures results in greater general metabolism than expos­
ure to the numerically equivalent constant temperature.
Headlee (191U)
studied the development of the grain aphis at constant and fluctuating
temperatures and found that the constant temperature is more effective
than variable ones.
His results (19U0) showed that constant tempera­
tures are far more powerful than variable ones on the development of
codling moth pupae and also for the development of Aedes aegypti (L.).
As far as A. aegypti is concerned, both 90° F. and 100° F. are postoptimal temperatures - as it will be shown later - and the results are,
therefore, not pertinent.
His results of further experiments (19hl)
are very different from his earlier work on this mosquito.
This time
he found a quite decided increase in the velocity of development under
the variable temperatures.
He explained it in this way:
"The underly­
ing and governing factor of such differences as exist in the variable
and constant temperatures is the accumulation of the required amount of
temperature, regardless of whether the temperatures in question come
from constant or variable sources."
This explanation met with a very
serious criticism on the part of Huffaker (19U2) who showed that in
Headlee’s variable and constant temperature lots the thermal units ac­
cumulated at exactly the same rate.
The experiments done by Peairs (191U, 1927), Janisch (192£, 1932),
Shelf ord (1927, 1929), Cook (1927), Parker (1930), Huffaker (19)42) and
others proved very definitely that insect development under variable
temperatures is faster than that under constant.
Shelford concluded
from his extensive studies on the development of codling moth under
actual weather conditions that the effect of normal daily fluctuations
- 19 -
of outdoor temperatures amounts to 7 - 8# more rapid development than
under constant temperatures.
Both Cook (1927) and Parker (1930) found
that the increased developmental power of the variable over the constant
was greater than 7 per cent for the insects and the conditions of their
experiments.
Cook found as high as a 37 per cent increase over the
constant for Porosagroti3 orthogonia Morr.,
and Parker an increase as
high as 70 per cent for the development of the eggs of the grasshoppers
Melanoplus mexicanus Saussure and Camnula pallucida Soudder.
Of special interest are results obtained by Huffaker (19U2) with
variable and constant temperatures on larval development of Anopheles
quadrimaculatus Say, because this species is quite comparable to Aedes
aegypti.
He stated that the highest degree of acceleration, 13.U per
cent, occurs when the low temperature is below 17° C. (high temperature
being from 2U.Ll° to 31.6 °C.) and when the continuous daily exposure
at the high temperature is 6 to 9 hours.
When, however, the low temper­
ature was about 19° C., (high 27° to 30.7° C.), 23° C. or 2Lu!?0 C. there
was retardation of 2 .7 , 2.3 and l.U per cent respectively, as compared
to the effect of constant temperature.
EXPERIMENTAL METHODS
The strain of Aedes aegypti (L.) used in these experiments was ob­
tained from the Mosquito Laboratory at the Ohio State University which
descended from those originally supplied in 19U3 by the U. S. D. A.
Bureau of Entomology and Plant Quarantine Laboratory, Orlando, Florida.
During the work herein reported seventy lfj-minute-old larvae at a time
were placed in glass jars of itOO cc. capacity with 35.5 cm2 surface
area.
The optimal population density (as well as optimal food amount)
was determined in preliminary experiments, as it is reported in the
next section.
Distilled water was used.
showed, the larvae of Aedes aegypti (L.)
As Shannon and Putnam (193k)
exhibit little food prefer­
ence and can survive for a considerable period of time on a minute
quantity of food.
They were fed powdered dog biscuit once a day as
recommended by Crowell (19U0).
16 mgrs.;
The optimal food amount was found to be
this was doubled for each succeeding instar.
Observations
of culture water revealed an abundance of infusoria at all temperatures.
The larvae were kept in complete darkness.
Beakers with three replicates in each case were placed in tempera­
ture-controlled cabinets at 13 different constant temperatures, a total
of 92 beakers and 36HO larvae being used.
Temperatures were mostly
accurate to plus or minus .2° C. for each cabinet.
Readings were taken
twice daily with a U. S. Bureau of Standards thermometer.
Relative
humidity based on differences between wet and dry bulb temperatures (F.)
was kept at 70° and was measured by a Model HA-2 psychometer (Bendix
Aviation Corporation, Baltimore).
The pH of fresh distilled water was 6.9 and the pH values during
-
21
-
the experiments varied very little but becoming slightly acid dcrnm to
6.3 which is still in the vicinity of the general optimum for this
genus (Senior-White, 1926).
countered.
No interference from this source was en­
At constant temperatures of 35>° C. and 36° ,C. the water was
changed each day in order to prevent any building up of a scum-film on
the surface caused by high food oxygenation at these temperatures.
The first-half figure of emergence or moulting is used as average
to indicate the velocity of development.
Under present conditions
this average is more critical with respect to temperature than would
be an average derived from total emergence.
-
22
-
CONSTANT TEMPERATURE EFFECT ON IMMATURE STAGES
As Parker (1930) showed, the optimal temperature and the general
temperature relationship for eggs of Melanoplus mexicanus mexicanus
differed greatly from the relationship for nymphs.
The stimulating
effect of cold temperatures on the hatching of this species is very
great.
The egg stage, however, occupies quite a different position in
the life cycle of this species from that of the hyraphs.
Each is
adapted in a different way to the environmental conditions which are
usually prevalent during the development of each particular stage.
This fact raises the question as to whether temperature studies should
be confined to a single stage.
The developmentally optimal constant temperature, in successive
stages in the development of an unspecialized insect, ought to have a
direct effect on the whole problem of the relative power of constant
temperatures in studies of metabolism.
When this optimal temperature
changes from one immature stage to another, it should change in some
consistent way.
If the value of a high constant temperature is maximal
only at the beginning and then decreases with increased exposure, we
would expect that the earlier instars would have a higher developmental
optimum than the subsequent instars, because the earlier instars had
received the greatest advantage from the initial exposure to the high
temperature, before the effect of high temperature became injurious by
the greater accumulation of heat.
It was shown in the preceding section that the exponential curve
of Janisch is a reasonable expression of the temperature-time relation­
ship in insect development.
Because it expresses the summation of an
- 23 -
accelerating effect at higher temperatures and a retarding effect at
lower ones which are represented by two members, positive and negative,
in the binominal expression of this exponential curve.
The develop­
mental velocity curves in Figures 1, 2 and 3 elucidate and confirm this
relationship.
The average time of development between larval stages
for lUO larvae at each temperature is expressed in hours and is plotted
as a caternaiy curve.
The velocity of development is expressed by the
reciprocal of the catemary curve and has the sigmoid form of the bio­
logical curve.
As a matter of fact, this reciprocal is of greater im­
portance because it shows more clearly the effects of extreme tempera­
tures at both ends of the optimal range.
First Instar
The developmentally optimal temperature for the first instar was
33.0° C.
1.
The stage was completed in 30 hours as can be seen in Figure
The data for the 10 constant temperatures are presented in Table 1.
The developmental velocity curve - reciprocal of the cat.ernary - shows
a remarkable conformity with these data.
TABLE 1
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the Yellow Fever
Mosquito, Aedes aegypti: First Instar
Temperature
°C.
Time
(inhrs.)
Velocity
12.U
15
18
21
2U
27
30
33
3k
35
31U
219
137
95
55
U5
36
30
32
33
.0032 .00U5 .0072 .0105 .0182 .0222 .0277 .0333 .0312 .0303
- 21* -
THE RELATION OF CONSTANT TEMPERATURES TO THE DEVELOPMENT
TO THE DEVELOPMENT OF THE IMMATURE STAGES OF THE
YELLOW FEVER MOSQUITO, AEDES AEGYPTI
Explanation - for Figures 1, 2 and 3
The catemary,
In the formula,
y - ^ (ax -f- a“x )
21 “ time,
and its reciprocal are plotted.
m is the time required at the optimum,
x is the temperature in degrees Centigrade above or below the optimum,
a is a constant which is 1.113 for the first instar, 1.1$2 for the
second instar, 1.179 for the third instar, 1.20U for the fourth instar,
1.1U7 for the pupal stage and 1.221*. for the period from hatching to
emergence.
VELO C ITY
H
PI
Z
■D
PI
TIME
IN
HOURS
3D
VELOCITY
PI
o
TIME
“
%Z -
IN
HOURS
- 26 -
The time required to complete the first instar varied from about
320 to 29.5 hours, correspondingly as the temperature varied from 12.0°
to 33.3° C. as can be seen on Figure 1.
33.3° C.
From above about 27.0° to
there is not a great difference in the time required for
completing this stage, but, if expressed by a percentage, the stage was
completed
3h% faster at the higher temperature.
The decrease in the
velocity of development above 33.0° C. corresponds to the hypothetical
curve.
These larvae which completed the stage at 33° C. represented
only 6l per cent.
Second Instar
The optimal temperature for the second instar was 32.8° C., as
can be seen in Figure 1.
The optimal time of development was 25 hours
which represents the shortest period of any stage of this species.
The
observed data at 10 different constant temperatures are given in Table
2.
Considering the catemary in Figure 1, it may be seen that the time
required for completing this stage also varied very much, from about
2U7 hours at a temperature of 12.0° C. to about
2h hours at 33*0° C.
Though the departure of the observed data from the hypothetical caternary are somewhat greater, the differences are not important when it is
considered that the observations were made at intervals of 8 hours.
- 27 -
TABLE 2
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the Yellow Fever
Mosquito, Aedes aegypti: Second Instar
temperature
°C.
12.J4
15
18
21
2h
27
30
33
3U
35
Time
(in hrs.)
252
178
120
75
38
33
30
25
27
30
Velocity
.0039 .0056 .0083 .0133 .0285 .0303 .0333 .0U00 .0370 .0333
Third Instar
The optimal developmental temperature for this stage was 32.0° C.,
as observed in Figure 2.
The optimal developmental time was 31 hours.
The form of the reciprocal of the caternary is very similar to that for
the first instar.
The numerical velocity values for the medial and low
temperatures, however, were greater which indicates that this stage at
medial and lower constant temperatures was completed in a shorter time
than was the first instar.
On the contrary, the numerical velocity
values for the temperatures above the medial are somewhat smaller and,
therefore, this stage required a slightly longer time for completion
of development at temperatures above the medial.
constant temperatures are presented in Table 3.
Observed data at 10
£
TIM E
£
VELOCITY
IN
HOOR8
VELO C IT
*
■vi
TIME IN HOURS
TABLE 3
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the Yellow Fever
Mosquito, Aedes aegypti: Third Instar
Temperature
c.
12.h
15
18
21
2U
27
30
33
3h
35
Time
(in hrs.)
281
201
106
79
U2
39
35
32
3U
35
Velocity
.0039 .00U9 .009U .0129 .0222 .0257 .0285 .0312 .029U .0285
Time of development varied from about 288 hours at 12.0° C. to 31
hours at 32.0° C. which is the developmentally optimal temperature for
the third instar.
Fourth Instar
The developmentally optimal temperature for the fourth instar was
31.0° C. as is shown on the velocity curve in Figure 2.
The time re­
quired to complete the fourth instar stage at this temperature was 53
hours, and in a range of 10 constant temperatures it varied from about
U26 hours at 12.0° C. to 53 hours at 31.0° C.
10 temperatures are presented in Table U.
The observed data at
- 30 -
TABLE
k
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the lellcw Fever
Mosquito, Aedes aegypti: Fourth Instar
Temperature
°G.
Time
(in hrs.)
Velocity
12. k
15
18
21
2U
27
30
33
3U
35
U20
301
168
116
72
63
58
55
69
7k
.002U .0033
.0059 .0086 .0138 .0158 .0172 .0182 .011*5 .0135
The important difference in the curve of development of this stage
when compared with previous curves is that the time required is almost
twice as long as that of the other instars.
The relationships of the
other instars are the same when compared to this stage which can be
demonstrated by prolonging the velocity axis in Figure 2 to twice its
present dimensions while the temperature axis remains the same.
As a
result, we would get a velocity curve which would resemble closely
the velocity curves of the previous instars.
alone the differing factor in this stage.
The time, therefore, is
This, however, is to be ex­
pected, because the fourth instar stage is actually a double stage in­
cluding the prepupal form, where the greatest growth takes place which
again requires a correspondingly longer time.
Pupal Stage
The optimal temperature
for the development of the pupal stage
was 31.3° C., and the required time at this temperature was 33 hours.
The completion of the pupal stage requires somewhat more heat energy
than does the first, second and third instars with the slight exception
- 31 -
in the case of the first instar where the numerical velocity values
for the lower temperatures are somewhat greater for the shorter time
of development and smaller for the post-medial temperatures.
The time
involved in the development, however, is nearly one-half of that re­
quired by the fourth instar.
The pupal period varied from about 276
hours at 12.0° C. to 33 hours at 31.3° C.
temperatures are given in Table
The observed data at 10
5.
TABLE 5
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the Yellow Fever
Mosquito, Aedes aegypti; Pupal Stage
Temperature
°c.
12. Li
15
18
21
2b
27
30
33
3b
35
Time
(in hrs.)
282
193
117
85
b9
b5
37
3b
37
bO
Velocity
.0039 .00^3 .0085 .0117 .020b .0222 .0270 .029b .0270 .0250
From Hatching to Emergence
In order to compare the total period of development with the com­
ponent stages the four larval instars and the pupal stage are here con­
sidered together as the developmental stage.
The data for this total
period of development - as represented by the caternary curve and its
reciprocal in Figure 3 - present a remarkable general uniformity with
all previous stages and offer no reason to consider the different
stages of this species separately.
For other species, whose ontogen­
etic form relationships are variously different, it might be necessary
to confine such a study to a single stage - as, for instance, in the
V E L O C IT Y
“O
_NJ
O
'FIGURE
TIME IN H 0 U R 8
-S
>
3
VE LO C ITY
N>
~o
TIME IN
K>
-
-
HOURS
- 33 -
case of egg and nymphal stages of the grasshopper, Melanoplus mexicanus,
as shown by the previously mentioned work of Parker.
The general action of constant temperature upon developmental
velocity of this species is presented in Figure 3, and the observed
data for 10 different constant temperatures are given in Table 6.
The
shortest time required from newly hatched larvae to emergence of adults
was about 170 hours at the optimal developmental temperature of 32.0° 0.
The time required from eclosion to emergence varied from about 1U72
hours or 61.3 days at 12.0° C. to 170 hours or 7.1 days at 32.0° C., ac­
cording to the caternary curve.
The actually observed values, however,
were 15U9 hours or 6U.5 days at 12. U° C. and agree rather closely with
the velocity curve.
TABLE 6
The Relation of Constant Temperatures to the Devel­
opment of the Immature Stages of the Yellow Fever
Mosquito, Aedes aegypti: Eclosion to Emergence
Temperature
°c.
Time
(in hrs.)
Velocity
15
18
21
2h
27
30
33
3U
35
15U9 1080
6U8
160
255
225
196
176
199
212
.ooliU
.0051
.0056
.0050
.00U7
12.U
.0006
.0009 .001^ .0022
.0039
-
3)4
-
COMPARATIVE DISCUSSION
The differences in the time and developmental temperature rela­
tionships from the first instar stage through to the pupal stage show as it cam be seen in Figures 1, 2, 3 - that there is a decided drop in
the optimal developmental temperature as the development progresses
from the first instar to the pupal stage.
This drop is consistently
going in the same direction from 33.3° C. for the first instar, about
32.8° C. for the second, 32.0° C. for the third, to about 31.0° C. for
the fourth instar and pupal stages, giving a difference of 2,3° C.
A very similar dropping of developmentally optimal temperatures
was found by Huffaker in Anopheles quadrimaculatus from 32.5° C. for
the first instar to 30.0° C. for the pupal stage.
According to this
author, there are two possible explanations of this phenomenon:
1.
The developmental efficiency of a given high temperature
is more and more reduced as more and more time is spent at that temp­
erature.
In other words, the initial rates of the metabolic processes
are not maintained.
This explanation seems to be supported by the fact
that larvae which had been reared during their total larval period at
32.5° C. died in later pupal stage, while larvae that had been reared
during the larval stages at some medial temperature and then as fourth
instar larvae transferred to water of 35.5° C. completed the pupation
at this higher temperature, thus escaping the accumulative, injurious
action of high temperature.
2.
There may exist different true optima at different stages.
"As the development proceeds and the form becomds more complex in its
metabolic demands, the problem of supplying the tissues with the nec­
- 35 -
essary constituents for anabolic processes and the removal of waste
products of metabolism becomes more acute.
The relative balance of
anabolic and katabolic processes is changed and, therefore, the orig­
inally optimal temperature no longer supports the greatest net product
of growth and development."
According to Huffaker both these explana­
tions are operative during the processes of development.
i)
The various immature stages differ considerably in the actual time
required for their completion.
As it can be seen in Figure 1, 2 and 3*
the fourth instar requires a longer time for its completion (almost
twice as much as the others) because of its greater total growth as
well as basic tissue transformation.
The next, in time required, is
the pupal stage and first instar, followed by the third and second
instar.
There is a remarkable resemblance between the developmental vel­
ocities of these two species, Aedes aegypti (L.) and Anopheles quadrimaculatus Say at the medial and post-medial temperatures, though the
developmentally optimal temperatures for immature stages of Aedes
aegypti are somewhat higher, circa 1° C.
There is, however, a deci­
sive prolongation of development of Aedes aegypti at low temperatures
as compared with the duration of development of Anopheles quadrimaculatus, reaching circa 1/5 greater number of days at the lower temperature
limit of development at 12.0° C. and decreasing correspondingly as the
temperature is approaching more closely the medial temperatures.
This
fact would suggest that the species of Aedes aegypti needs more therm­
al units to complete the immature stages at extreme low temperatures
when compared with Anopheles quadrimaculatus. *
The results of the minimum duration of development of immature
- 36 -
stages - as indicated by Reed and Carroll (1911) for Aedes aegypti 180 hours - are in conformity with those obtained in the present work
at developmentally optimal temperature.
MacGregor (1931)> however, ob­
tained somewhat different results with a strain of A. aegypti at the
Wellcome Entomological Field Laboratory when they were reared at a con­
stant temperature of 30° C.
The time of development for a generation
varies from 2U0 to 360 hours which is higher than presented in this
work.
He does not mention, however, the larval mortality which is con­
siderable at this temperature.
Shannon and Putnam (193U) consider the optimal temperature (not
developmental) for this species to be from 23° to 27° C. at which temp­
eratures the oupation took place at 1UU and 168 hours respectively.
The
optimal temperature range, even if considered from the point of highest
percentage of survival, is too low and the time required for larval
development is unusually short as compared with those from Huffaker's
and the present work, particularly the development at 23° C. constant
temperature is hard to account for as it differs by one day only from
that at 27° C.
The retardation of development of four larval stages
from 27° C. down to 23° C. as presented by the writer's data makes 3*5
days which is also corroborated by Huffaker's data.
Headlee (19U0, 19U1) has published very confusing results on temp­
erature effects upon larval development of Aedes aegypti.
In 19UO he
showed that constant temperatures are far more powerful than variable;
three times greater effect at constant rather than variable at 29.U° C.,
for instance.
Also, the time required for completion of development of
immature stages at the mentioned constant temperature (29.U° C .) is too
long i.e. 2h0 hours.
Very probably lack of food was another factor
- 37 -
affecting the development for the mortality rate was rather high for this temperature.
26% -
In 19hi he published data very different from his
previous work on Aedes aegypti.
In this instance he found a decided
increase in the velocity of development under variable temperatures when
these varied daily from 10° C. to 26.7° C.
He explained it on the basis
of the "speed of accumulating the thermal constant."
He further ex­
plained that his "present work indicates that the underlying and govern­
ing factor of such differences as exist in the variable and constant
temperatures is the accumulation of the required amount of temperatures,
regardless of whether the temperatures in question come from constant
or variable sources."
Under the conditions of his experiments, however,
the rate of accumulating thermal units was exactly the same.
As was mentioned Dreviously, Huffaker showed that the highest per­
centage (13.h5) of acceleration of development occurs when the low temp­
erature was near 15° C. and high from 2U.h° C. to 31.6° C., exposure
being at least 6 hours.
"When the low temperature was about 19° C.,
23° C, or 2U.5° C., there was a retardation of 2.7, 2.3 and l.U per cent
respectively compared to the constant.
Under natural conditions, how­
ever, during the breeding season of Aedes aegypti changes of tempera­
ture circa 10° C. do not exist in larger bodies of water and, therefore,
no appreciable acceleration in development can take place, except prob­
ably in some microhabitats (empty containers, rain barrels, run cover
systems, etc.).
In early and late portions of the breeding season,
particularly, such differences in temperatures may occur.
- 38 -
THE RELATION OF TEMPERATURE TO THE SURVIVAL OF IMMATURE STAGES.
THE THRESHOLD, LOW AND HIGH LETHAL TEMPERATURES, OPTIMAL SURVIVAL
The difficulty of determining the exact threshold of development
for a given stage of an insect is in practical work very great since it
is hardly possible by any method to register a very small amount of
development going on at a very slow rate.
The threshold of development
of Aedes aegypti has not been determined exactly.
Using the graphic
method of Shelford (1927) and Bodenheimer (1930), which consists of
drawing a straight line through the empirically found velocities and
intersecting the temperature axis, the theoretical threshold would lie
in the vicinity of 8.8° C.
This is, indeed, far below the highest low-
temperature death point (11° C.).
At 9° C., which is lethal tempera­
ture for all larvae, some non-measurable development was observed.
larvae died before completing the first instar stage.
The
At 6° C. there
was no observable development and larvae were dead after 8 hours.
Therefore, the threshold would be approximately between 7° and 8° C.
Constant temperatures of 10° C. and 11° C. were lethal to all lar­
vae.
At 12° C. only 8 individuals developed into pupae, at which stage
they died.
At 12.U° C. only
died while attempting to emerge.
per cent completed development but
This temperature, therefore, may be
considered too low to complete the development for all practical pur­
poses.
At l£° C. only 18 per cent developed to adults.
Above the optimum, at 3U° C., only 59 per cent completed develop­
ment.
At 35° C.
3 per cent pupae did emerge.
It might be mentioned
here that these results were obtained after several attempts.
When
water was not changed and larvae were fed the usual amount of food once
- 39 -
daily, a film of scum -was produced on the surface and larvae died dur­
ing the fourth instar stage.
When the water was changed daily and the
same amount of food was introduced twice per day, the larval and pupal
mortality was reduced and 3 per cent of emergence was obtained.
This
might suggest that the death at high temperatures may be closely re­
lated to starvation at lower temperatures, because the nutritive sub­
stances at these almost lethal temperatures are oxidized so rapidly
that the supply does not keep pace with metabolic processes.
At the
temperature of 36° C. all larvae were dead at the end of the fourth
day, being in the third instar stage at this time.
vae died before completing the first stage.
At 38° C. all lar­
The pupae reared at 27° C.
until pupation and then transferred to 35>° C. were able to emerge.
This indicates that the injurious effects of high temperatures are ac­
cumulative .
The survival percentages are given in Table 7 and the mortality
curve is plotted against the developmental velocity curve in Figure U.
The peak of survival, 100 per cent, is at 27° C.
This temperature,
therefore, was taken as the optimal temperature for maximal biotic
potential as opposed to "developmentally optimal temperature" used in
these experiments which was found to be 32.0° C. for this species.
For
the temperatures above the optimum or those below the point where the
mortality curve cuts the velocity curve, there is a sharp reduction in
survival as the temperature is decreased or increased as in the former
case.
VELOCITY
TEMPERATURE
*C
MORTALITY
- ai -
TABLE 7
Constant Temperature Relationships to Mortality of
Immature Stages of Aedes aegypti
Temperature
in °C.
12.U
15
18
21
2h
27
30
33
Mortality
in %
96.5
82
27
12
1
0
U
18
3U
35
97
THE RELATION OF SURFACE-VOLUME RATIO
TO THE DEVELOPMENT OF AEDES AEGYPTI LARVAE
- U3 -
INTRODUCTORY REMARKS AND METHODS
A great deal of attention has been given to the relationship be­
tween larval development and various environmental factors in mosquito
breeding places.
None, however, as far as the writer could locate,
was performed with respect to the effect of surface area upon larval
development.
In these studies an attempt has been made to find the
relationship between the different surface areas and the subsequent
changes which take place in the culture water and thus affect larval
development itself.
In order to study the effect of surface area to water volume the
volume was kept constant, 1000
2!i-hour-old larvae were used.
cc. in each case.
One-hundred-seventy
This population was found in previous
experiments to be the optimal density for the 1000 cc. volume.
A
series of eight jars (Figure 5) of different size were used which vai^
ied in surface area from 28.2 square centimeters to £30.6 square cent­
imeters and the corresponding depths from 35-3 centimeters to 1,8
centimeters.
Thus, the surface area available per larva varied accord­
ingly from .16 to 3.03 cm^.
The larvae were reared to pupal stage, at
which time they were removed, permitted to dry for four hours on filter
paper at controlled roam temperature and then weighed.
Distilled water
of pH 6.91 was used and then during the development measured at U-day
intervals by a Beckman pH meter.
Forty mg. of standard ground dog
biscuit was found the optimal amount in previous experiments as a food,
which amount was doubled for each next instar.
The experiment with
three replicates was conducted in a controlled temperature cabinet at
27° C.
- uu -
FIGURE 5
-
145
-
RESULTS OF SURFACE-VOLUME RATIO INVESTIGATION
During the period of larval development the hydrogen-ion concen­
tration in the jar with the smallest surface and the greatest depth
became definitely more acid, changing gradually from a 6.91 pH to a
5.50 pH,
The water with the larger surface area (538 square centi­
meters) and accordingly smaller depth became slightly more acid,
changing from 6.91 pH to 6.52 pH.
The data are given in Table 8.
The rate of development of the larvae was faster in the jars with
the larger surface area than in the jars with the smaller surface, the
difference being 2.2 days.
As it can be seen in Figure 6, there is a
direct correlation between the developmental velocity and the weight
of pupae.
Those in jars with smaller surface and which required the
longest time to develop produced the smallest pupae which averaged 3.10
milligrams in weight.
Those reared in the jars with the largest sur­
face exposure and which required the shortest time for development pro­
duced the larger pupae which averaged U.32 milligrams in weight.
Fur­
thermore, the mortality (3.8 per cent) was greater in the jars with
the small surface exposure and greatest depth while in those jars with
a large surface and small depth no mortality occurred.
The data obtained from these eight jars of varying surface show:
1.
When a constant volume of water is used with a uniform
population of larvae, the acidity of the water increases during larval
development with the decrease of surface area and the increase in depth.
2.
Time of development is shorter in jars with larger sur­
face area and less acidity, and the pupae are larger.
3.
The larval mortality decreases correspondingly with the
—
U6
—
increase in surface area, decrease in depth and less increase in the
acidity.
table
pH of W a t e r
After After
4 days 8 days
8
Time of
develop­
ment of
Mortal­ Weight
Surface Depth of pupae
in
ity in of pupae
area in water in
hours per cent
cm
cm
in mg
Surface
area
avail
able ;
larva
cm 2
Jar
Tos.
Begin­
ning
A1
6.91
6.05
5.50
28.2
35.4
233
3.8
3.10
0.16
A2
6.91
6.17
5.61
38.5
26.0
225
2.6
3.20
0.22
A3
6.91
6.25
5.69
78.5
12.7
220
2.6
3.48
0.44
•P"
-j
A4
6.91
6.32
5.86
122.6
8.1
216
2.0
3.58
0.71
A5
6.91
6.42
5.95
162.7
6.1
200
1.8
3.62
0.93
A6
6.91
6.57
6.38
283 .3
5.5
192
0.7
3.86
1.61
A7
6.91
6.65
6.47
379.9
2.6
182
0.0
3.98
2.17
A8
6.91
6.72
6.52
530.6
1.8
180
0.0
4.32
3.03
u
VELOCITY
WEIGHT
CM
j£ _ I 2 £ ®
FIGURE) 6
- U9 -
QUANTITATIVE AND QUALITATIVE EXAMINATION OF THE MICROFLORA FOUND
IN THE WATER USED FOR REARING
AEDES AEGYPTI
LARVAE
Samples for quantitative analysis of the microflora of the water
used for rearing were taken
1 ) before the larvae were added, 2 ) twenty
minutes after the larvae had been added, and 3 ) from all containers at
the end of the developmental period.
These samples of 1 ml. were di­
luted from Is10 to 1:10 million, plated on nutrient agar and incubated
at 37° C. for U8 hours.
The highest number of microorganisms was
157,000,000 per ml., found in the water with the largest surface area
and very slight acidity (pH 6.72).
The number of microorganisms de­
creased simultaneously with increasing acidity;
in the water with the
smallest surface area (28.2 cm^) and the pH 5.5 there were only
2U,600,000 microorganisms per ml.
However, in the distilled water alone
at the beginning of the experiments 10 microorganisms per ml. were found
and in the samples taken twenty minutes after the introduction of larvae
1,030 per ml. were present.
These results indicate that there are far
more microorganisms present in the almost neutral hydrogen-ion concen­
tration than in the stronger acidic media.
The qualitative analysis was performed under aerobic and anaerobic
conditions.
stain,
The genera were identified by
1) morphology and Grave's
2 ) cellular arrangement and motility,
3 ) pigmentation, and
U) by biochemical activities including the ability to grow on differ­
ential and selective media.
From these studies it was possible to
identify the following genera:
- 50 -
1)
Staphylococcus
2)
Bacillus
3)
Alkaligenes
U)
Chromobacter
5)
Corynebacterium
6)
Shigella
Various yeasts and molds were also noted, but no attempt was made to
identify them as to genus.
In addition to the aerobic incubation anaerobic incubation was
applied to samples streaked on nutrient agar for U8 hours at 37° C.
Clostridium was identified as the most prevalent genus under these
conditions.
-
£l
-
DISCUSSION
As hydrogen-ion concentration is an important factor in many bio­
logical processes, various studies have been made on this subject i&
mosquito breeding places.
Reviewing literature on this subject Mac­
Gregor (1927) made the following generalization:
acidophile and alkalinophile species.
"There are definitely
There are also a few species
which, to some extent, tolerate both acidity and alkalinity.
The
majority of pond-, swamp- and river-breeding anopheline species are
alkalinophile.
A lesser number of anopheline larvae have, however,
been found to occur in acid waters and are acidophile.
Nevertheless,
there does not appear to be any record of what is generally an acido­
phile anopheline species being found also in alkaline water, or vice
versa."
Senior-White (1926) gives hydrogen-ion toleration limits for
some species.
He states that for Anopheles maculatus it is £.9—9*6 pH,
for A. leucosphyrus 6.1-6.9 pH, Stegomyia albopicta .U.3-9.7 pH, Culex
fatigans 7.0-9.7 pH.
Woodhill (1938), however, was able to grow Culex
fatigans in a pH range from U.2 to 9.0.
Wigglesworth (19U2) reared
Aedes aegypti in bacteria-free medium of pH U.O, apparently with no ill
effect on mosquito larvae.
species
large.
The exact limits of pH tolerance for this
were not determined.
The range, however, seems to be rather
When the pH changes naturally the larvae can tolerate a rather
low pH concentration with only 3*8 per cent mortality at a £.£ pH.
Using chemically buffered solutions in the range from pH 2.0 to 11.8
the writer found that the first instar larvae were able to develop in
the range £.0-7.0 pH, while fourth instar larvae transferred into
these (2.0 to 11.8 pH) ranges pupated and emerged as adults at pH
14.0-11 .8 .
The influence of hydrogen-ion concentration on the microorganisms
makes laboratory experiments difficult.
According to Bates (19U9)
there is no way of determining whether the relation of mosquito breed­
ing to pH is direct or indirect.
The latter seems more likely to him,
since acidity influences the microorganisms very much.
As it can be seen from Figure 6 there is a direct relationship be­
tween the surface area and hydrogen-ion concentration changes.
The pH
of the water was changed toward acidity more rapidly and to a greater
extent in containers with smaller area than in those with larger sur­
face.
Since all other factors were constant the question arises as to
the causes of these changes in pH.
Because 0 2 and N 2 present in the
air do not react with water and so do not produce changes of pH con­
centration, this may be due to several other factors:
1.
Carbon dioxide present in the air does react with water,
thus producing carbonic acid (CO2 + H 2O * H 2CO3 ) , but due to its very
low concentration in air (0 .01$) this effect is very probably neglig­
ible .
2.
Microorganisms themselves affect the pH concentrations
by their metabolic processes.
Since, however, quantitatively they were
far more numerous in almost neutral conditions, they alone could not
be responsible for the increase of hydrogen-ion concentration in con­
tainers with smaller surface and greater depth.
3.
The greatest effect upon hydrogen-ion concentration
(under present experimental conditions) must have been carbon dioxide
produced by the larvae themselves.
In the container with greater
depth and smaller surface carbon dioxide produced by larvae at the bot-
- 53 -
torn does not escape to the air as fast as carbon dioxide released at
the surface.
Therefore, in the former, there is more carbonic acid
built up in the -water than in the latter and correspondingly the acid­
ity increases more rapidly in the container with smaller surface and
greater depth.
Senior-White (1926), after performing many experiments with var­
ious species, also stated that even when the total concentration is
due to more than dissolved gases alone the carbon dioxide is undoubtedly
a prime factor in the causation of hydrogen-ion concentration.
The development under the more acid conditions was slower than in
almost neutral water media, but it is not possible to say whether this
was a direct effect or indirect through the retardation of bacterial
development.
Woodhill (1938) rearing Culex fatigans in a pH range
from U .2 to 9.0 found also considerable retardation of development at
both extremes.
Harold (1926) is of the opinion that the pH of the water is of
minor importance to the developing larvae and that the factor of prime
importance is food.
The pH concentration, on the other hand, has a
direct effect upon the microorganisms of the larval community which in
turn serve as a source of larval food.
This most probably accounts for
the retardation of development and also for the slight mortality which
took place under more acid conditions.
- 5U -
THE EFFECTS OF DIFFERENT WAVE LENGTHS OF
LIGHT UPON THE DEVELOPMENT OF AEDES AEGIPTI
IMMATURE STAGES
- 55 -
INTRODUCTORY CONSIDERATIONS
A study of the effect of light upon biological processes of ani­
mals and plants is attracting very wide attention at the present time.
There is no need to stress the importance of solar radiation as a prim­
ary factor in animal ecology.
Because the present work deals with the
effects of different wave-ranges of the light spectrum uoon the metabol­
ism of A. aegypti in such arrangements as they may occur in nature, it
seems necessary to present a short discussion on the subject before
presenting the results of these studies and discussing their effects.
There are two kinds of natural light affecting animal life which
differ not only physically but also physiologically as well:
and diffused light.
direct
Each of these types of rays has its own intensity,
quantity during a given period and its special composition.
Most of the
investigations in the past dealt with measurement of intensity of direct
rays because the methods for that were more complete.
How does the intensity of direct rays depend on the geographical
latitude?
Michelson has shown (Domo, 192U) that, contrary to common
belief, the intensity of normal direct rays does not vary too much with
the latitude.
So, in the extreme north, Lapland, in July and August
the mean for day-maximum is 1.22£ g. cal./min. cm^ , while for Siam
(1U° lat.) it is 1.22 g. cal. and for the Indian Ocean (U° lat.) it is
1.20 g. cal. (Szymkiewicz, 1926).
This similarity in calarie sun-ef-
fect in the tropics and in the north is accounted for by the diminish­
ing of the rays caused by the low stand of the sun and by the small
absolute humidity.
Quite different is the relationship of the rays' intensity to the
-
altitude.
56
-
The higher the altitude the thinner becomes the air
layer
through -which the rays have to pass and, therefore, the intensity of
these rays increases accordingly.
In addition, the increase of solar
intensity varies with the seasons.
According to Dorno (op. cit.) the
increase of intensity from sea level to 2500 meters amounts to about
50$ more in winter and 20% more in spring than during summer and fall.
Consequently, the rise of intensity together with altitude is more im­
portant in winter and spring.
The intensity of the diffused radiation varies probably more than
that of direct radiation.
It depends not only on the altitude of the
sun but also on cloudiness which, contrary to popular idea, not only
does not decrease the intensity of solar radiation but usually increases
it.
When we do not take into consideration the heavy rain clouds, we
may say that the light of the cloudless sky is least intensive.
intensity at noon varies from .0? to .1 g. cal.
The
With the sinking of
the sun the diffused radiation decreases slowly at the beginning and
more rapidly as the evening advances.
The clearer the sky and the more
whitish shade the sky has the weaker is its intensity and vice versa
(Kalitin, 1927).
When the white clouds appear, its intensity increases
very much to 0.3-0.6 g. cal./min. cm^
which is 25 to 50 per cent of the
noon intensity.
As far as the different latitudes are concerned, according to
Savinof (192U) and Dorno (1927), the intensity is even very often
greater in the north because of the whitish shade which is character­
istic for the northern sky.
If, then, we take into consideration the
greater cloudiness in the north, we can expect that, on the average,
the diffusive radiation will be higher in the north than in the south.
- Si -
As far as altitude changes are concerned we can say that with a clear
sky and increased altitude a decrease of the absolute and relative
diffusive light takes place.
One has to keep in mind, however, that
this refers to the cloudless sky which in the mountains is more or
less an exception.
Particularly during summer at the higher altitude
the intensity of diffused light is increasing, and, in general, the
effects of diffused radiation in the mountains is usually greater than
at sea level.
All these possibilities have to be taken into consideration while
evaluating the effects of radiation.
All light which is absorbed -
no matter what wave length - is changed into radiant energy and affects
the metabolism of living matter in one way or another.
Therefore, the
spectral composition of the natural radiation is of special interest
for ecology.
The spectrum of the natural radiation ranges from 30,000 2 infra­
red (Krueger, 1929) down to 2910 £ ultraviolet.
From U000 2 to about
7600 2 are the wave lengths of the visible spectrum:
above the upper
limit there is invisible infrared, beneath the lower one is invisible
ultraviolet.
The effects of waves of different lengths upon the metab­
olism of poikilothermal animals, particularly those of ultraviolet,
are of very different nature.
This subject, however will be considered
in the next section.
While in sunlight practically only wave lengths to 30,000
the earth surface emits also long wave rays.
2 occur,
These heat waves of the
earth's surface have their maximum (at l5° C.) in the neighborhood of
90,000
% - 100,000
2.
With increased warmth of surface the maximum
goes over to shorter waves, which may have also biological effects
(Krueger, 1929).
The maximum distribution of energy in the visible sun spectrum
lies, with the sun at zenith position (65°) in summer, in yellow and
green (5000
$.) and moves with the sinking sun (at 30° ) to the red
(7000 2) according to Kimball (192U).
At the zenith position of the
sun, the total energy of sun radiation is divided as follows: about
60 per cent for infrared, about UO per cent for visible light and
only less than 1 per cent for ultraviolet rays.
The largest percentage of the radiation intensity at this posi­
tion of the sun is that of infrared.
It is understandable, therefore,
that the infrared rays have a considerable effect upon the temperature
of irradiated animals.
As the water vapor strongly absorbs the red and infrared rays,
this intensity fluctuates parallel with vapor content of the air.
The
intensity of the infrared and red radiation is, therefore, submitted
to considerable changes throughout the year.
In tropical lands, for
instance, this radiation loses almost 30 per cent of its energy, ac­
cording to Ivanoff (1929).
The absorption of the infrared intensity
by water vapor varies very much according to the wave lengths of the
rays.
A layer of water vapor 1 meter thick may absorb the infrared
rays of wave lengths 9200 X, 11,570 £, 13 ,000-lh ,500 & almost 70 per
cent, those of 17 ,500-19,500
% about 80 per cent, above 21^,000 X almost
100 per cent according to Krueger (1929).
The water itself of a depth
of 10 cm. absorbs the entire energy of the infrared rays.
Despite
this fact the infrared rays may still considerably affect the devel­
opmental velocity of immature stages of the insect tinder consideration
because they, particularly in later instars, spend almost all of their
- 59 -
time at the surface and, therefore, are exposed to the infrared radia­
tion.
The make-up of ultraviolet rays, as was mentioned previously, is
less than 1 per cent of the total solar radiation.
It is a well estab­
lished fact at the present time that these rays of various wave lengths
have strong physiological effects of quite different nature upon or­
ganisms.
By actinometric measurements Mayer (1925), Dorno (1927) and
others showed that the lower end of the spectrum is limited directly
at the beginning of the area of strong physiological effect (in vicin­
ity of 3000 X ).
According to these measurements the range of ultra­
violet rays varies with the height of the sun;
3160 X,
at I4O 0 - 3220 X
and at 60° - 2980 X.
they reach at 10° Consequently the noon
sun has more active ultraviolet rays than morning or evening sun, in
summer more than in winter.
The maximum of physiological effect co­
incides with these rays very closely.
Their intensity varies very
much according to the sun’s height, altitude and transparency of the
air:
at the sun position from 15° to 60° at Oberengadin in the Alps
the intensity increases 17 times while the photometric illumination
increases only 1.5 times, and the intensity of the total radiation
rises 20 per cent.
But in spite of this great fluctuation the spectrum
does not go under 2910 X .
This fact, therefore, proves that all ex­
periments upon the physiological effects of these rays in nature per­
formed with artificial sources of ultraviolet waves shorter than
2910 X are not comparable at all to the effects of ultraviolet rays
upon living matter as they occur in nature.
Furthermore, under natural
conditions the ultraviolet rays never act upon the* organisms by them­
selves, being always combined with the visible and infrared radiations.
-
60
-
Herein we have a possible explanation of the absence of any deleter­
ious action of the ultraviolet radiation upon the metabolism of ani­
mals, if such would be produced by the action of ultraviolet rays alone.
The reduction of actual damaging effects of ultraviolet by mixed rad­
iations (luminous plus infrared rays) will be discussed later.
In order to locate the ranges of the wave lengths under consider­
ation it seems advisable to indicate briefly their position in the re­
lationship to the gamut of electro-magnetic waves.
These waves ex­
tend from cosmic rays at one end, the shortest, to the long radio waves
of about fourteen thousand meters or more.
cosmic rays, X-rays, ultraviolet, violet;
The sequence is as follows:
then, visible spectrum from
U000 X to 7500 X - violet, blue, green, yellow range and visible red;
infrared (not visible) - heat waves - Hertzian waves - and radio waves.
The shorter waves including ultraviolet are characterized by their
chemical activity, the longer waves including infrared are character­
ized by heat and chemical activity.
-
61
-
HISTORICAL REVIEW
There is only a little published information on the effects of
infrared radiation upon insects, and even this is mostly from the as­
pect of a possible control of storage or household insects in their
adult or larval stages.
The writer was not able, however, to find any
reference in the literature as far as it was available dealing with the
effect of infrared radiation upon insects in aquatic habitats.
And
yet there is no reason to doubt that in nature, particularly under fav­
orable meteorological conditions, as mentioned previously, the inten­
sity of infrared radiation may represent a greater part of solar energy
and consequently must have a considerable effect on biological proc­
esses of some of these forms.
Excluded are, of course, forms living
deeper in the water or which do not spend at least some time of their
development at the surface because water, as stated before, absorbs
much of the infrared rays.
These insects, however, benefit at least
indirectly from the infrared heat energy through their medium whose
temperature is affected by the infrared radiation.
MacLeod (19U2) studied the effects of infrared radiation upon the
American cockroach.
Adult roaches killed at a distance of 18 inches
from an incandescent lamp, irradiated on the ventral side, died in
from 2^- - U minutes while the air temperature was 26° C. and the temp­
erature at the surface of the insect was U3° C.
When irradiated on
the dorsal side, U - 6 minutes was required to kill the insects, the
temperature of the tegmina reaching k7° C.
He is assuming that this
is the lethal temperature for roaches.
Headlee and Jobbins (1938) found that 30.9 per cent infrared
-
62
-
energy penetrated both of the forewings and 2.U per cent penetrated all
wings plus the dorsal integument of the American cockroach at a dis­
tance of 10 or 12 inches from the incandescent lamp.
They also found
that 0.1U to 0.83 per cent infrared energy penetrated 0.03 inch of var­
ious wheat products.
Krueger (1929) found that the integument of the
body of Pamassius apollo absorbed the infrared rays almost wholly
while the wings reflected a considerable percentage.
Frost et al (I9l*lt)
studied the lethal exposure and cause of death by infrared radiation on
the larvae and adults of the confused flour beetle and the mealworm,
adults of the bean weevil and black carpet beetle.
They concluded that
the death of insects irradiated by infrared rays is due to increased
internal body temperature.
In all cases the internal temperature at
the end of the minimum period necessary to produce death approached the
average fatal temperature which, according to Uvarov (1931) is 50° C.
Wigglesworth (1950) gives the fatal temperature for mealworm larvae as
U2° C.
Adults of the flour beetle were killed at lower temperature
(108° F.) than larvad (128° F.) because of their greater rate of heat
absorption due to their darker color.
The possibility of using infrared radiation for insect control
was first suggested by Blazer (19U2).
He constructed a battery of in­
frared lamps for treating rice to control injurious species.
According
to Cotton (19U1) 10 minutes exposure at 60° C. temperature is fatal to
all grain insects.
Preliminary tests showed that it may be possible to
control these insects by infrared if a satisfactory means of heating
infested grain was developed.
Working with Drosophila Kaufmann, Hollaender and Gay (19U6) have
shown that pre-treatment with near infrared radiation significantly in­
- 63 -
creases the frequency of X-ray-induced chromosomal rearrangements as
compared to the frequency obtained from X-ray controls.
They showed
that a generalized temperature change does not account for the modifica­
tion of break frequencies but that some other factor must be involved.
They further stated that the region of effectiveness in the infrared
spectrum lies in the neighborhood of 10,000 8 and concluded that the
changes produced by these rays are permanent and very probably of a
physical-chemical nature.
With little having been done with the lethal effects of ultraviolet
rays on adult or immature insects, it seems to be necessary to refer
first to the various publications dealing with ultraviolet radiation upon
microorganisms and plants.
Many and varied experiments have been per­
formed upon bacteria (Dugger, 1936) since it has been discovered that
sunlight in the short ultraviolet range of the spectrum possessed lethal
qualities.
Later experiments proved that only those waves shorter than
3100 8 had bactericidal value, especially those from 2000-2950 8 .
These have lethal qualities 10 to 12 times greater than the longer waves
from the ultraviolet spectrum (Horen, 19U7).
Reports on the effect of ultraviolet radiation on cell division
are in part contradictory;
both stimulation and inhibition of cell div­
ision have been described.
Bovie and Hughes (1918) found inhibition of
cell division in paramecia;
however, with doses which produced only
short periods of inhibition, inhibition was followed by an acceleration
of cell division.
in paramecia.
Giese (19U5) also found inhibition of cell division
According to his results the wave lengths of 2537* 265U
and 280U 8 are highly effective;
less effective;
21*83 and 3025 8 are significantly
while wave lengths of 3130 and 3660 8 have no effect
-
at all in retardation.
6k
-
Maximum of retardation appeared at 280U X sug­
gesting cytoplasmic protein absorption.
His results seem to furnish
the material for a rational interpretation of the effects of ultra­
violet radiations upon the rate of cell division in various organisms.
They indicate that while both nucleoproteins and proteins of the albu­
min type may be affected, the predominant effect of non-lethal dosages
which has the most lasting consequences is upon the nucleoproteins.
Mayer and Schreiber (193U) studied the effect of ultraviolet radiation
on tissue cultures and found growth inhibition.
Decreased mitotic activity as a result of ultraviolet treatment
with the full spectrum of the quartz mercury arc has been reported by
Politzer and Alberti (192U) in the cornea of salamander larva and
Moellendorff and Laqueur (1938) in tissue cultures of chick fibroblast/.
The effects of monochromatic radiation of a limited number of wave ­
lengths have been investigated by Mayer and Schreiber (193U) in fibro­
blasts in tissue culture, and by Jones, Jacobs and Hollaender (19U0)
in nematode eggs.
They found that the maximum effect in retarding cell
division was produced by radiation shorter than 2900 X, and that at
longer wave:lengths the effectiveness of the radiation decreased as
the wave lengths were increased.
Schechtmann (19UU) reviewed the literature of the influence of
ultraviolet rays on early embryonic development;
he quotes Hinrichs,
Higgins, Sheard and Brandes as having found stimulating effects under
certain circumstances, while he himself could find only inhibitory ef­
fects.
Harris (1925) working with rats found that the ultraviolet
radiation exerts a stimulating action on the gaseous metabolism of
small animals.
This stimulant action of ultraviolet radiations accord­
-
6$.-
ing to him is completely annulled by the presence of visible radiations.
Mme. and M. Henri (1912) have also observed that the slowing down of
protoplasmic movement by ultraviolet rays was much reduced if illum­
inated by visible light at the same time.
Later L. Hill (192U) has
shown that the immobilizing effect of ultraviolet rays on infusoria
could be considerably reduced by the mere addition of red light.
Harris
explained it as "herein we have a possible explanation of the absencd
of any measurable effect of mixed radiations on the gaseous metabolism
of animals, also of the freedom of human beings exposed to direct sun­
light from any deleterious effects of ultraviolet rays, in virtue of
the nullifying action of the luminous radiations."
The experiments performed with plants (Dugger, 1936;
Johnston,
1936;
Popp and Charlton, 1938) have been even more numerous and inten­
sive.
The results obtained tend to confirm the belief that the middle
and short ultraviolet rays definitely retard growth or check it com­
pletely.
The apparent effects are stunting, curling of the leaves and
necrosis of the tissues and the actual destruction of the epidermal
cells.
According to Popp (1926) and Ivanoff (1926) the exclusion of
the waves shorter than 3120 £ , however, does not have any damaging ef­
fect on the development of plants.
Definite effects on the reproductive functions of insects irrad­
iated by ultraviolet rays are known to occur.
has been the insect commonly used.
Drosophila melanogaster
Mutations were observed (Schultz,
1936) after irradiation of the insects.
Translocation of the sperms
(Demerec et al, 19^2) has occasionally been observed.
Working with
eggs of the bean weevil, MacLeod (1933) found that, rays less than 3126 £
were definitely injurious, causing lethal effects which varied- inversely
-
with the age of the eggs;
66
-
but that longer rays may have been benefic­
ial, for the emerging treated larvae weighed more than the controls.
The first instar larvae were killed by exposure to the above mentioned
rays while adults exhibited no marked effects;
iduals, however, were sterile.
eggs from these indiv­
Abnormalities of external structures
were apparent in forms from both irradiated eggs and adults.
Larvae
developing from irradiated adults had usually prolonged pupal period.
Carlson and Hollaender (19UU) observed inhibition of mitosis in
grasshopper neuroblast and noted that all phases of mitotic early
prophase was retarded most markedly.
Eggs of grasshoppers (Ray and
Bodine, 1938) subjected to the ultraviolet rays showed a decrease of
hatching, accompanied by an increase in respiration.
tions in sensitivity were observed.
Extreme varia­
According to Ray and Bodine the
ultraviolet rays act mainly on the embryo rather than the yolk or egg
components.
Bertholf (1933) irradiated bees with ultraviolet to deter­
mine if beneficial effects could be induced, but they were harmed by
longer exposures, though short doses gave slight indications of bene­
ficial effects.
Irradiations with waves shorter than 2970 $ were
decidedly harmful.
Horen (19U7) working with ultraviolet rays on both larvae and
adults of Tenebrio molitor concluded that this radiation does not have
an apparent effect upon either adults or larvae.
The rate of activity
of the insect, however, decreases after prolonged exposure to the rays.
In his experiments, considerable infrared was involved, because the
final temperatures of insects, arrived at by exposures of 3 and lf>
minutes for distances of 8 and 18 inches, were
ively.
7h° and I4O .!?0 C. respect­
As a result of the work which has already been done on the ef-
- 67 -
feet of ultraviolet rays, it is clear that these rays may have a very
great effect;
also, that the effect may vary from one insect to
another and during the different stages of the life history of any
individual insect.
-
68
-
EXPERIMENTAL METHODS
Seventy 15-minute-old larvae were placed in beakers of U00 cc.
Distilled water of pH 6.70 was used.
experiments.
Food was used as in the previous
All experiments with light of different wave lengths were
conducted in a controlled temperature cabinet at 27° C.
A light source
was placed over the covered beakers as shown in Fig. 7.
For the vis­
ible spectrum a fluorescent lamp containing two 15-watt white tubes
was placed above the beakers at a distance of 8 cm.
The spectrum of
this lamp ranges from 3130 X to 7500 X as shown in the photospectro­
graph, Fig. 9, which is within the limits of visible rays in the nat­
ural spectrum.
As a source of infrared rays, an infrared commercial
lamp of 2^0 watts, 115 volts was placed above the beakers at a dis­
tance of 51 cm.
to 10,570 X?
The lengths of these waves range from about 7500 X
This lamp produced waves of even shorter lengths as
shown in the photospectrograph;
tensity.
these, however, were of reduced in­
In the same way (51 cm. above) was mounted a commercial sun­
lamp of 275 watts, 110-125 volts as a source of ultraviolet light.
This lamp produced a discontinuous spectrum of wave lengths from 29UO X
through the visible range up to 5500 X, and a continuous spectrum in
the infrared range.
In order to eliminate any kind of reflection the bottom, sides
and doors of the cabinet were covered by black paper board.
Each ex­
periment was performed with light of different intensities, beginning
with .5 foot-candle up to 256 foot-candles in a geometric ratio:
1, 2, U, 8, 16, 32, 6U, 128, 256.
0, .5*
In order to reduce the light inten­
sity to a desirable level covers made from onionskin paper were placed
- 69 -
FIGURE 7
- 70 -
upon the beakers.
These covers (Fig. 7) were 12| cm. high and 11 cm.
in diameter so they -would give plenty of space around the beakers.
They had two side openings at the top in order to permit good circula­
tion of air around the beakers and at the surface of the water.
All
beakers with the covers were placed on the wire screen so the air could
enter from the bottom.
Covers for controls (0 foot-candle) were made
from the black paper board and were shielded by another carbon sheet
in order to eliminate any radiation.
Measurements of the light intensities were taken with the Weston
Illumination Meter, Model 603, which indicates the illumination in footcandle units.
Because the illumination of a surface is inversely pro­
portional to the square of the distance of the surface from the light
source (E • i/R^) it is obvious that the illumination at the bottom of
the beakers was smaller than that at the surface of the water.
Taking
into consideration the high absorption of infrared rays by water, these
differences in light intensities between surface and bottom will be
still greater in the case of infrared light.
Larvae moving from the
surface to the bottom of the beakers were, therefore, exposed to differ­
ent light intensities which lay between the limits of maximal (at the
surface)and minimal (at the bottom) light intensity.
When reference is
made to foot-candles in this work, it always means the maximal intensity
measured on the surface of the water.
Calculated light intensities at
the bottom for fluorescent and ultraviolet light as compared to the
surface intensities are given in foot-candles as follows:
-
1
0
.1
.2
.
-=3
0
.3
.7
l.U
8
16
.
.5
-
CO
0
C \l
Intensities at
Surface for
All Sources
Intensities at
Bottom for
Fluorescent
Intensities at
Bottom for
U.V. & I.R.
71
1.6 3.2
2.9
5.9 11.9
32
6U 128
256
6 .U 12.9 25.8 51.7
23
U?
95
191
Because the Weston Illumination Meter is standardized on tungsten
filament light at one color temperature, measurements made of illumin­
ation from other sources will require some correction.
The values of
measurements of infrared and ultraviolet light are, therefore, relative
only.
In the following table are given the relative values of actual
measurements of infrared and ultraviolet at different distances to
show the relationship to measurements on fluorescent light.
Distance from light source
in cm.
Poot-candles for
fluorescent
Foot-candles for
infrared
Foot-candles for
ultraviolet
30
U5
60
6.2
2.7
1.5
U.o
l.U
.9
0.0
2.2
.8
Larvae were exposed to ths given light without interruption during
the whole developmental period until the first half (35 pupae) emerged.
The pH values varied from 6.71 to 6.21 under fluorescent light, from
6.60 to 6.05 under infrared and from 6.68 to 6.15 under ultraviolet
light.
species.
This is still in the vicinity of the general optimum for this
No interference from this source was encountered.
adults were counted in 8 hour intervals.
Emerged
- 72 -
RELATION OF LIGHT OF DIFFERENT WAVE LENGTHS TO DEVELOPMENT
OF IMMATURE STAGES
Relation of Fluorescent Light to the Velocity of Development and
Emergence Density of Aedes aegypti:
Immature stages of Aedes aegypti, particularly larval stages, are
photophobic and react very quickly to any light intensity.
Their dev­
elopmental velocity, however, is inverse to the illumination within
certain limits.
in 22U hours;
When kept in complete darkness the first half emerged
the time of development decreased with increased light
intensity reaching its optimum in the neighborhood of 16 foot-candles.
At this light intensity the development is accomplished at 200 hours
which is 12 per cent shorter than in complete darkness.
At both 8 and
32 foot-candles the time of development increases somewhat but is still
8.8 per cent shorter than in darkness.
At intensities below U foot-
candles and above 6I4 the time of development is the same, as it can be
seen in Figure 8, being still U.U per cent shorter than in darkness.
The optimal range of illumination is, therefore, for this species be­
tween 8 and 32 foot-candles under the artificial daylight conditions of
fluorescent light.
The data for time of development and emergence den­
sity are given in Table 9.
The density of emergence is spread more as the time of development
becomes longer, being 6U hours in darkness and I48 hours under optimal
light intensity.
range.
There was no mortality under this light intensity
- 73 -
TABLE 9
Relation of Intensity of Fluorescent Light to the Time of
Development and Emergence Density of Aedes aegypti:
Showing Adults Emerged
lime in Hours
Candles
176
18U
192
200
208
216
22a
232
2ao
2a8
256
6
0
6
9
12
17
15
11
7
.5
12
11
16
15
13
3
2
1
15
12
17
13
8
a
1
2
13
15
19
12
8
3
2
13
ia
16
12
9
a
k
8
h
9
15
20
ia
9
16
5
8
17
22
11
7
a
19
16
17
9
6
12
15
16
ia
11
a
11
ia
17
12
ia
2
8
15
16
15
ia
a
32
6U
128
256
Relation of Infrared Light to the Velocity of Development and Emergence
Density of Aedes aegypti:
As it can be seen from Fig. 8 the velocity of larval development
is veiy much affected by the infrared rays.
Already one-half foot-
candle produces a substantial acceleration of development, shortening
the developmental period by 2 days or 21 per cent.
This acceleration
gradually increases further until it reaches its maximum at the inten­
sity of 32 foot-candles.
At this and subsequent light intensities
larvae completed their development and emerged as adults in 150 hours.
I
DEVELOPMENTAL
8
t
v e l o c it y
TIME
IN H 0U R 8
- 75 -
This is 3 days or 33.0 per cent earlier than larvae not exposed to the
infrared radiation at the same temperature, and 2.1 days earlier than
larvae exposed to the optimal light intensity of visible rays.
Know­
ing that rays of long wave lengths produce heat energy in the exposed
larvae, one would expect some acceleration in the larval development.
The actual reduction - 1^0 hours - however, is even below the time re­
quired for development at the optimal developmental temperature which
was 170 hours.
This phenomfcnen, however, will be discussed later.
The density of emergence is higher and time correspondingly
shorter than it was under fluorescent light conditions.
given in Table 10.
infrared radiation.
The data are
There was no mortality under all intensities of
- 76 -
TABLE 10
Relation of Intensity of Infrared Light to the Time of
Development and Emergence Density of Aedes aegypti;
Showing Adults Emerged
in HoUrs
Candles 128 136
Ihh 152 160 168 176 18U 192 200 208 216 22U 232 2U0 2lt8
0
3
7
9
3
.5
5
lh
20
13
9
6
1
10
15
16
13
10
6
5
2
6
8
1U
15
1U
8
h
8
11
19
15
11
h
10
16
18
13
8
5
8
13
18
lh
12
5
8
16
32
h
9
15
20
17
5
6U
6
10
15
18
15
6
128
h
8
lit
21
lh
9
256
5
10
16
23
10
6
10
15
12
8
7
Relation of Intensity of Ultraviolet Light to the Velocity of Develop­
ment and Emergence Density of Aedes aegypti;
As the photospectrograph shows, Fig. 9, in this light source a
considerable amount of infrared light is involved.
The developmental
velocity, therefore, is a result of the two actions accelerating, af­
fected by infrared rays, and retarding, conditioned by ultraviolet rays.
Until the illumination intensity reaches the U foot-candles the accel­
erating effect is prevalent as can be seen in Figure 8, and the curve
of the time of development follows very closely that of infrared radia­
- 77 -
tion.
After this optimum of development was reached and with increas­
ing light intensity, the retarding effect of ultraviolet rays becomes
more expressive and decreases the velocity of development gradually
until the light intensity reaches 6U foot-candles.
At this intensity
the retardation of development amounts to 21 per cent as compared to
the velocity of development under the influence of infrared radiation
at the same intensity.
At the still higher intensities - 128 and 256
foot-candles - as a result of chemical reactions of ultraviolet radia­
tion upon the living cells the effects are even more noticeable.
At
the intensities of ultraviolet with definite effects of retardation
in the development rather marked deformaties of larvae, particularly
fourth instar, were noticed.
The larvae were shorter than normal and
the thoracic region was widened remarkably.
investigation along this line was undertaken.
However, no comparative
None of the larvae
survived the 12 hours exposure to the 128 foot-candles intensity of
ultraviolet and hone survived 3 hours exposure to the 256 foot-candles
illumination intensity, while the second instar exposed to 128 and
256 foot-candles of ultraviolet were able to survive longer i.e. I4.O
and llj. hours respectively.
The density of adult emergence is shorter than both under infra­
red and fluorescent lights.
Data are given in Table 11,
- 78 -
TABLE 11
Relation of Intensity of Ultraviolet Light to the Time of
Development and Emergence Density of Aedes aegypti:
Showing Adults Emerged
Time in Hours.
Candles____________152 160 168 176 18U 192 200 208 216 22U 232
0
7
.5
12 23
17
10
8
1
10 25
18
12
5
2
10 19 28
9
h
U
12 25 18
9
6
8
U 23 25
10
8
16
2 26 2U
11
7
32
18 28
13
8
3
6U
13 21
16 10
8
9 13
13
15
128
All died after 12 hours exposure
256
All died after
3 hours exposure
2h0 2U8
8
5
- 79 -
COMPARATIVE DISCUSSION
Infrared Light
Hie results of MacLeod (1933)> Headlee and Jobbins (1938), Frost
et al (19UU) and others who, applying infrared radiations, raised the
insect body temperature to the lethal point, are not considered here.
These experiments have been conducted with terrestrial insects in open
air where the insects were not able to lose their rapidly accumulated
heat energy to the environment in the same rate as they acquired it
and, therefore, died when their body temperatures reached the lethal
point.
This effect of infrared radiation may find a practical applica­
tion in the future in household and storage insect control.
The effects of infrared radiation upon insects in an aquatic hab­
itat, however, as presented in this work, is quite different.
The
dark insect cuticula absorbs practically all infrared radiation (ex­
cept a small reflected amount) as long as this radiation reaches the
insect.
Infrared radiation, converted into heat energy, raises the
insect body temperature but, simultaneously, the insect loses it to
the water medium very rapidly because of the high conductivity coef­
ficient of the water.
The result of this accunrulating-losing heat proo
ess depends on several factors:
temperature of surrounding water, dur­
ation of insect exposure to infrared rays, intensity of infrared and
the rapidity of insect movements as well.
Bearing these things in mind and also remembering that the con­
stant temperature at which the present experiments were conducted was
27° C. the question now arises as to,
1)
what factor or factors are responsible for the remarkable
- 80 —
developmental acceleration in larvae of Aedes aegypti under the infra­
red radiation, and
2)
how much are these factors contributing to this acceler­
ation?
As it is shown in Figure 8 the highest acceleration was achieved
at 32 and subsequent foot-candles, i.e. 3 days shorter as compared to
the control and 2.1 days as compared to the optimal development under
fluorescent light.
And even when this acceleration is compared with
the velocity of development at the optimal developmental temperature
(32° C.) the time required for completion of development under the in­
fluence of infrared is still almost one day shorter.
This difference
in developmental velocity indicates at once that there must be another
factor, besides temperature, which is able to speed up the rate of
development more than even the optimal developmental temperature does.
There is no doubt- that the infrared rays produce heat energy and,
until recently, it was the only effect ascribed to infrared.
Heat
produced by absorbed infrared radiation which raises the body temper­
ature, as it was proved in many cases, is, therefore, one factor af­
fecting the developmental acceleration of immature stages.
The writer
is of the opinion that the body temperature of larvae was not much
higher, if at all, than that of the surrounding water and, therefore,
could not have produced such an acceleration of development as actually
took place in this case.
This is supported by the fact that at the
optimal developmental and post-optimal temperatures (as shown in the
section on constant temperature effect) there is a considerable per­
centage of mortality accompanying these temperatures.
After the optim­
al developmental temperature is surpassed, on the other hand, the ac-
- 81 -
cumulating thermal units result in retardation of development.
None
of this evidence is given in the present case, therefore, the body
temperatures of larvae must have been very close to water temperatures
or at least considerably lower than is the optimal developmental temp­
era ^ture and could not cause the present acceleration by itself.
Kaufmann, Hollaender and Gay (19U6) experimenting on modification
of the frequency of chromosomal rearrangements induced by X-rays in
Drosophila used infrared radiation as pretreatment and posttreatment to
X-rays.
They have shown that in both cases the infrared radiation
significantly increases the frequency of X-ray-produced chromosomal
rearrangements in Drosophila as compared to the frequency obtained from
the X-ray control.
nature.
They stated that these changes are of permanent
The region of effectiveness in the infrared spectrum lies in
the neighborhood of 10,000 &.
From their data it can be inferred that
the effect of infrared radiation is not achieved by general tempera­
ture changes but rather by a definite chemical or physical change within
the cell which is reflected in the increased cell activity and in­
creased response of the chromosomes to X-ray radiation.
Swanson and
Hollaender (19U6) working on the same subject with Tradescantia ob­
tained similar results.
The increased growth in larvae of Aedes aegypti suggests that the
cell activity was very much affected by the infrared radiation in the
same way.
This growth stimulating effect of the infrared radiation
very probably contributes more to the speed of development of these
larvae than temperature effect.
There is a strong reason to believe
that, under favorable meteorological conditions, particularly in dif­
fused light, this stimulating effect of infrared radiation plays an
-
82
-
important role in shortening the developmental period of immature
stages of this species.
Fluorescent Light
As far as the effect of visible light upon insects is concerned
Chapman (1931) made the conclusion "that if the light conditions are
sufficient for the host plant to grow normally, the insects will grow
normally, and that those which do not require living host plants do
not require light".
Laboratory experiments of many workers with the
effect of light on larval development seem to show, in general, that
it is not a very important direct factor.
Thus Fielding (1919) found
that the larvae of Aedes aegypti grow equally well in the presence
or absence of light.
Similar results were obtained also by Jobling
(1937) with Aedes aegypti, Culex pipiens and C. fatigans.
These
authors, however, do not mention the time of development.
As it can
be seen from Table 9, 10 and 11 the larvae reared in complete dark­
ness do not show any mortality, yet the time of development was al­
most one day longer when compared with development at 8 to 32 footcandles intensity.
The results, plotted in Figure 8, show a definite
acceleration of development at this range of light intensity even of
smaller intensity.
Frost, Herms and Hoskins (1936) working with Theobaldia incidens
also found that small daily doses of visible light speeded develop­
ment of this species.
In general, there is a common impression among
the workers with mosquito larvae that visible light is helpful in
the laboratory culture not only because of its direct effect on larval
development but also because of its indirect effect.
Most algae re-
- 83 -
quire sunlight, and algae are usually favorable in larval culture
media, either as food for the larvae or as an aid in maintaining a
balance of dissolved gases.
In breeding places in nature, even in shaded areas, there is al­
ways sufficient light intensity from diffused light.
It can be con­
cluded, therefore, that certain acceleration of larval development is
caused even by the visible rays alone.
Ultraviolet Light
As the spectrum of the ultraviolet light source shows (Figure 9)
a considerable amount of infrared radiation was here included although
of smaller intensity than in the infrared alone.
The presence of these
heat-energy-producing waves in the ultraviolet spectrum was very prob­
ably responsible for the acceleration of development, going almost
parallel with the curve of developmental activity of infrared up to
the 1; foot-candles intensity (Figure 8).
At this point the develop­
mental velocity is the highest, and dropsagain
as the radiation in­
tensity increases to 128 foot-candles.
In the consideration of the characteristics of the various parts
of the spectrum of light it has been pointed out that the shorter
wave lengths are characterized by their chemical activity.
One would,
therefore, expect these short waves to have a great effect upon the
biological processes of the organism.
It is a firmly established fact
by the present time that this effect is, in general, retardation or
complete stoppage of these processes.
Though ultraviolet radiation
does not penetrate the tissues of insects very deeply it does pass
through the outer layers to affect cell division in the mitotically
- 8U -
active basal layers.
Further, it has been suggested that the high
percentage of skin cancer in the South (Mountin and Dorn, 1939) may
be due to excessive exposure to solar ultraviolet radiation.
Since
the carcino-genetic effects of ultraviolet radiation have been ade­
quately demonstrated (Grady, Blum and Kirby-Smith, 19U3).
Decreased mitotic activity in insects as a result of ultraviolet
radiation shorter than 3126 X has been mentioned previously.
The
chemical nature of this effect of ultraviolet radiation is not known
exactly.
Kaufmann and Hollaender (19U6) experimenting with ultra­
violet radiation on Drosophila stated that "'When high intensities of
2^37 X are used, the chemical structure of ribose as well as desoxyribose nucleic acid is broken down".
If serum proteins are treated in
vitro, radiation by ultraviolet waves affects an increase in viscosity,
a decrease of the colloid osmotic pressure, and a homogenizing of the
electrophoretic pattern (Davis, Hollaender and Greenstein, 19U2),
Ap­
parently unfolding of the protein occurs first, then splitting of the
unfolded molecules and finally aggregation.
Kaufmann and Hollaender
think that, if proteins of comparable structure exist within the chrom­
osomes of the spermatozoa of Drosophila, it is possible that the energy
absorbed following the use of 2537 X may initiate the unfolding of the
proteins and the depolymerization of the thymonucleic acid.
In the present experiments the shortest wave length used was
29UO X.
Yet the death of larvae caused by the intensities of 128 and
256 foot-candles indicates that similar chemical processes in the
cells of the larvae took place.
When 15-minute-old larvae were exposed
to the ultraviolet radiation of these intensities they died in 12 and
3 hours respectively.
When second instar larvae were exposed to the
-
8*
-
same intensities they died in LiO hours at 128 foot-candles and lit hours
at
2$6 foot-candles intensities.
IVhen later instars we re exposed to
these intensities of ultraviolet, more time was needed to cause death.
This would indicate that more highly developed forms are less affected
by the ultraviolet rays.
This would be in accordance with the Bergonie-
Tribondeau rule which states that a progressive differentiation of a
cell is less affected by the shorter wave radiation (X-rays and ultra­
violet) (Holthusen, 1920).
tigators;
This rule was confirmed by several inves­
Perthes, Bardeen (Hertwig, 1911) working with frog eggs
and Holthusen (1920) with eggs of Ascaris. and others.
Contrary to
these, however, are the results of experiments performed by Ruppert
(192U) and Seide (1926) on eggs of Ascaris.
They found that the em­
bryos in their later stages of development are more affected by the
short wave radiation than the earlier stage of the embryonal devel­
opment.
Referring to natural light conditions and realizing that the ul­
traviolet radiation represents less than 1 per cent of total solar
radiation and that the ultraviolet never reaches the intensity of 128
or 256 foot-candles one may conclude that the ultraviolet radiation
under natural light conditions does not affect metabolic processes of
the immature stages of Aedes aegypti nor produces deformations in any
appreciable rate.
- 86 -
FIGURE 9
- 87 -
SUMMARY
The catemary formula
y =* jj£ (ax -f a“x )
derived from two simple
exponential' functions, one representing an accelerative and the other
an inhibitive effect of increased temperature, seems to be the most
adequate method for expressing the velocity of insect metabolism.
The
time-temperature relationship in the development of Aedes aegypti
corresponds very closely to the reciprocal of the caternary curve.
The constant temperatures reaction upon the development of the
yellow fever mosquito, Aedes aegypti, has the same general form for the
total period of development as for the individual immature stages.
There is, however, a decided drop in the optimal developmental temp­
erature as the development progresses from the first instar to the
pupal stage from about 33.3° C. to 31° C.
The general optimal devel­
opmental temperature is at about 32° C., and the time required to com­
plete development from newly hatched larvae to adults varies from
about 15U9 hours, or
at 32.0° C.
days, at 12.U° C. to 170 hours, or 7.1 days,
The shortest time required to complete each successive
stage is near 30 hours with the exception of fourth instar larvae which
required almost twice as much time.
The threshold of development for
this species is at about 7.1>0 C. while the highest lethal low tempera­
ture is about 11° C. and the lowest lethal high temperature is about
36° C..
It is shown furthermore that the high temperatures have an ac­
cumulative injurious effect.
The surface-volume ratio affects time of development, size of
pupae, hydrogen-ion concentration and microflora.as well.
The acidity
of the water increases during larval development with the decrease of
- 88 -
surface area and the increase in depth.
The time of development is
shorter in jars with larger surface area and less acidity, and the
pupae are larger.
The larval mortality decreases correspondingly
with the increase in surface area, decrease in depth and less increase
in the acidity.
The carbon dioxide produced by larvae is considered
as a prime factor in increasing the hydrogen-ion concentration under
the described conditions.
The number of microorganisms decreases simultaneously with in­
creasing acidity and decreasing surface area.
As the most prevalent
genera there were identified:Staphylococcus, Bacillusa Alkaligenes,
Chromobacter, Corynebacterium and Shigella under aerobic incubation
and Clostridium under anaerobic incubation.
Under fluorescent light of wave lengths from 3130
to 7500 X
the time of development was shorter, reaching its optimum, 200 hours,
in the neighborhood of 16 foot-candles as compared to the development
in
complete darkness at 27° C. which was 22li hours.
Infrared light of wave lengths from 7500 X to 10,57® £ speeds up
the development of immature stages considerably.
At light intensities
of 32 foot-candles the development is accomplished in 150 hours which
is 33 per cent earlier than with larvae not exposed to the infrared
radiation.
The opinion of other workers that the stimulating effect
of infrared radiation increasing the cellular activity is far more
powerful and effective in larval metabolism than heat energy produced
by infrared radiation is verified by the present investigation.
The ultraviolet radiation of intensities of U foot-candles and
higher has a retarding effect on development.
At intensities of 168
and 256 the first instar larvae did not survive 12 and 3 hours expos-
- 89 -
ure respectively.
The writer feels that this corroborates the theory
of the nature of the deleterious effect of ultraviolet as ascribed to
chemical activity of the ultraviolet within the cell.
The writer is well aware that the data presented here are results
of only basic investigation of a few of the many phases inherent in a
study of mosquito ecology.
These results can, however, be of assist­
ance in yellow fever mosquito control in determining possible popula­
tion density and time of development under certain given temperature
and light intensity conditions.
During the course of experimental
work many questions arose which remain unanswered due to time and facil­
ities limitations.
Also, many problems came up which might be the
foundations for further and more complete investigation in this aspect
of ecology.
Some of these include the rearing and observation of de­
formed larvae and pupae arising through the use of ultraviolet radia­
tion.
The consistency of these deformities and the subsequent adult
peculiarities pose an interesting problem.
Much more complete work
needs to be done with the microorganisms in cultures.
Work on their
types, survival, new introductions and relationship to pH has not been
investigated to any great extent.
The application of the results of
work under controlled laboratory conditions to natural conditions
presents many questions particularly with the consideration of light
intensity, temperature and altitude, the latter of which has been
shown to be of great importance in natural infrared radiation.
- 90 -
BIBLIOGRAPHY
Agrell, I. 19U7. Temperature and metabolism in insects.
Zool. 39A(10). 1-U8.
Arkiv.
Arrhenius, Svante. 1889. Ueber die Dissociationswarme und den Einfluss der Temperature auf den Dissociationsgrad der Elektrolyte.
Ztschr. Phys. Chem. U:96-116.
Bachmetjew, P. 1901. Experimentelle entomologische Studien vom
physikalisch-chemischen Standpunkte aus. Band I. Temperaturverhaeltnisse bei Insekten. W. Engelmann, Leipzig.
1907* Experimentelle entomologische Studien vom physikalischchemischen. Standpunkte aus. Band II. Einfluss der aeusseren
Faktoren auf Insekten. Staatsdruckerei, Sophia,
Bates, M. 19U9. The natural history of mosquitoes.
Company, N. Y.
The Macmillan
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(
AUTOBIOGRAPHY
I, Julius Alexander Rudinsky, was b o m in Pukanec, Slovakia,
August 10, 1917*
I passed the maturity examination in 1939 at Zniov
after attending for eight years the Classical Gymnasium.
I enrolled
in the University of Prague in 1939 but returned home in 19U0 when the
university was closed by occupational forces.
From 19U0 to 19UU in­
clusive I studied Forestry at the University in Bratislava and passed
the final state examinations in November, 19UU.
In the same year I
left my native country because of war events in that area.
In 19U5 I
received an appointment as Assistant Instructor in Dendrology at the
University of Munich.
When this university was closed, in 19U6, I
enrolled in the University of Goettingen where I completed the courses
for the Ph. D. in economy in 19U9.
By sponsorship of The Ohio State
University I received a permanent visa for the United States and came
to Columbus in December, 19U9*
After spending two quarters in English
and history courses, I was admitted to the Graduate School in the
fall quarter of 1950, and chose entomology as a subject closely related
to forestry.
In 1951 I was appointed as a Research Fellow in the Ohio
State University Research Foundation on a project sponsored by the
United States National Institutes of Health, which position I have held
until the present time.