74
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
ation which is a prerequisite for such a development,
and further that the selection pressure of different
host plant communities is sufficient to cause changes
in the gene frequencies in the insect population.
The distance between the localities of the two
populations in the field was 2 ^ miles. There were
a number of woodlots between the two localities.
Apparently this barrier was giving a sufficient isolation between the insect populations. L. lineolaris
is an active insect, but it does not move in great
number over long distances. Thus, Haseman (1918)
states that most of the bugs found in a nursery in
the spring matured and passed the winter in the
immediate vicinity of the nursery. And it is well
known that the border rows of orchards and nursery
stock are much more likely to be injured than those
in the interior of the blocks (Woodside 1950). According to Dobzhansky (1951) two populations of a
species are allopatric when they are farther apart
than the average distance between the places where
an individual of the species and its offspring are
produced. This average distance in the case of L.
lineolaris is probably less than the 2 ^ miles between
the two localities. The sampled populations were,
therefore, allopatric (geographically isolated). That
genetic differences arose between two populations
under these conditions is in agreement with the
statement that "discontinuities in plant ranges arranged so that one segment of the insect population
found itself in a different plant community from
the other, and isolated, would assist in the differentiation of distinct gene frequencies in the two segments of the population" (Dethier 1954).
[Vol. 56
The experiments on different populations indicate
strongly that geographic races specially adapted to
the plant community may evolve when sufficiently
isolated populations of L. lineolaris live in different
plant communities. If these plant communities consist of cultivated crops (as was the case with the
alfalfa population), it appears that an insect population may develop an increased ability to survive
and multiply on the crop and consequently cause increased damage.
REFERENCES CITED
Aamodt, O. S., and J. Carlson. 1938. Tests of the
resistance of alfalfa varieties to Lygus bugs. Wisconsin Agric. Expt. Sta. Bull. 440, pt. II: 1-67.
Cochran, W. G., and G. M. Cox. 1957. Experimental
Designs. New York: John Wiley & Sons, Inc.
611 pp.
Dethier, V. G. 1954. Evolution of feeding preferences
in phytophagous insects. Evolution 8: 32-54.
Dobzhansky, T. 1951. Genetics and the Origin of
Species. 3d ed. New York: Columbia University
Press. 364 pp.
Haseman, L. 1918. The tarnished plant bug and its
injury to nursery stocks {Lygus pratensis L.).
Missouri Agric. Expt. Sta. Res. Bull. 29: 1-26.
MacLeod, G. G. 1933. Some examples of varietal resistance of plants to insect attacks. Jour. Econ.
Entomol. 26: 62-66.
Painter, R. H. 1951. Insect Resistance in Crop Plants.
New York: The Macmillan Company. 520 pp.
Taksdal, G. 1961. Ecology of plant resistance to the
tarnished plant bug, Lygus lineolaris (P. de B.).
M.S. thesis, Cornell University, Ithaca, New York.
Woodside, A. M. 1950. Cat-facing and dimpling of
peaches. Virginia Agric. Expt. Sta. Bull. 435: 1-18.
A Study of Termite Feeding Relationships, Using Radioisotopes1
ELIZABETH A. McMAHAN 2
Department of Zoology, The University of Chicago, Chicago, Illinois
ABSTRACT
Food exchange relationships of large (N) and small also have reflected relative numbers of microorganisms
(n) nymphs were studied in a dry wood termite, Crypt- in the hindgut. Termite size did not appear to influence
otcrmes brcvis (Walker), the food transfers being feeding relationships in the experimental situation.
traced by means of radioisotopes. Nymphs of both sizes Strontium-labelled donors lost a much larger percentage
were allowed to feed for 5 days on wood that had been of their nuclide via pellets than did cobalt-labelled
labelled with either strontium-85 or cobalt-57, and were donors; the strontium tended to be concentrated in the
then confined as "donors" with nonradioactive N and n malpighian tubules, the cobalt in the hindgut. It is
recipients in nonradioactive termitaries. After 2 days suggested that the symbiotic protozoa and bacteria contogether the termites were measured for radioactivity, centrated the cobalt. Pellet production was at the rate
and comparisons were made of relative amounts acquired of about 0.65 pellet per termite per clay. Tests showed
by iV and by n recipients when confined with N as that soldiers confined in radioactive termitaries did not
opposed to n donors. Large and small nymphs appeared become radioactive unless a nymph was also present,
to feed at approximately the same rate when relative supporting past observations that soldiers are entirely
size was taken into account. Soldiers and supplementary dependent on colony mates for food. The molting phase,
reproductives had smaller feeding capacities than had as expected, affected the amount of radioactivity acquired
nymphs of the same weight, judging from relative and donated, and caused cessation of pellet production.
amounts of radioactivity acquired, but differences may
Food exchange between individuals of the colony
1
A portion of this paper is based on part of a thesis submitted in partial fulfillment of requirements for the degree of
Doctor of Philosophy at the University of Hawaii in 1960. Accepted
for publication January 2, 1962.
2
Present address: Department of Zoology, The University of
North Carolina, Chapel Hill, N. C.
is one of the chief integrative mechanisms among
social insects. It helps the community to feed itself,
appears to be the basis of mutual recognition, and
is a means of inter-individual communication that
permits effective division of labor among workers
1963]
MCAIAHAN : TERMITE FEEDING RELATIONSHIPS
(Ribbands 1953). In termite colonies it is probably the method by which factors affecting caste
differentiation are transferred, and in those families in which cellulose digestion is carried out by
symbiotic protozoa contained in the termite hindgut, it is the means by which faunation and refaunation of the gut occurs.
Studies of feeding relationships within colonies
of social insects have resulted already in better
understanding of colony organization. A promising experimental technique employed in some of
these studies has been the use of radioisotopes in
tracing food exchanges between members of a
colony. So far the tracer work reported has been
concerned with the social Hymenoptera (Nixon
and Ribbands 1952; Oertel et al. 1953; Wilson
and Eisner 1957). The present study has extended
the application of the tracer technique to problems
of termite feeding relationships. The primary aim
has been to see if patterns of food exchange based
on caste, instar, or some other biological category
would be demonstrated.
The exchange of food between termite individuals
is of two types: stomodcal, the mouth to mouth transfer of salivary secretions, and proctodeal, the solicitation by one termite of part of the fluid content of
the hindgut of another. The relative frequency with
which a given type of feeding occurs depends, apparently, on the termite species.
The. present study was carried out entirely with
a drywood species, Cryptotcnncs brevis (Walker). It
is a member of the family Kalotermitidae, in which
there is no true worker caste. Its method of food
exchange appears to be mostly of the proctodeal type,
with stomodeal feeding very infrequently observed.
Proctodeal feeding is usually initiated and terminated
by the recipient, although prospective donors have
been observed to offer food to other termites, and
donors often terminate feeding by walking away.
Grasse (1949) has described the donor's part in the
feeding process as resulting from a defecatory reflex triggered by tactile stimulation by a recipient.
Observations on (\ brevis have indicated that the
recipient does more than simply to ingest a droplet
of fluid voided by the donor. It appears to maintain a definite hold on the donor's abdomen, and
termination of feeding is signalled by a releasing
jerk or plucking movement. A recipient can actually
restrain a donor and prevent his walking away during feeding.
Preliminary observation of fragments of Cryptotcnncs colonies showed that all possible feeding combinations between different types of individuals
(castes, instars, and sexes) could and did occur, except that first and second instars were almost never
solicited as donors. There seemed to be a tendency,
however, for large nymphs to solicit preferentially
from other large nymphs, and for small nymphs to
solicit from small. The subsequent experiments were
designed to yield quantifiable results for evaluating
each of the different termite types as donor and as
75
recipient, when tested in all possible feeding combinations.
Termites were made radioactive by feeding them
on wood that had been soaked in a radioisotope
solution and dried. They were then paired with
nonradioactive termites. The amount of radioactivity
(counts per minute) transferred from donor to recipient in a given feeding combination was considered
an indication of the relative strength of that particular feeding relationship.
EARLY EXPERIMENT (1959-1960)
The first experiment (McMahan 1960) will be
summarized briefly here. It was carried out at the
University of Hawaii and involved a comparison of
radioactivity (strontium-85) transferred within all
combinations of the following categories: large
nymphs, small nymphs, and adult soldiers of both
sexes. Wide variations in amounts of radioactivity
were acquired and transferred, even within a single
type of feeding combination, and differences in average gut capacities of the three major termite types
made evaluation extremely difficult. Furthermore, an
experimental unit consisted of a pair of termites only,
so that no individual termite had a true choice situation in feeding. If it fed from another termite at all
it had to feed from its partner.
The results of this first experiment were mostly
inconclusive insofar as factors influencing feeding
relationships were concerned. Its chief contribution
lay in the techniques worked out.
Other findings from this first experimental period
were more readily interpretable. A test was made
of the hypothesis that C. brevis soldiers are unable
to feed directly from wood but are completely dependent on colony mates for food. A total of 32 soldiers
were confined in groups of from two to eight in
radioactive wooden termitaries for 1 week. Members
of a group had access to each other but not to
nymphs. There were 19 survivors, varying in individual radioactivity counts between 0 and 13 counts
per minute, with an average of 6 cpm. Random variation in background counts could have accounted for
all these figures. The indication was strong that none
of the soldiers had fed during the period, except from
each other. These 19 soldiers were then paired for
a week with nymphs that had access to radioactivity,
and then retested. Cases in which the soldier died
or its partner died or molted were discarded because
of the probability that feeding was thereby altered or
prevented. Ten soldiers with active, nonmolted partners survived the week. They showed a rise in radioactivity from a previous average of 5 cpm to one of
135 cpm. These results are in line with past conclusions regarding the dependence of soldiers upon
colony mates for nourishment.
Data were also accumulated showing that during a
molting phase the acquisition of radioactivity by recipients was lowered or stopped, that feeding by
other termites was denied by donors, and that pellet
production ceased.
76
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
MAIN EXPERIMENTS (1960-1961)
In an attempt at further investigation of the possibility of patterns of food exchange within the colony,
another series of experiments was planned and carried out at the University of Chicago. These tests
were conducted along the same general lines as before, but with the following improvements. Recipients were given a choice of donors in a given test
situation, and only termite size (age ?) was investigated for its possible effect in determining feeding
relationships. Two series of tests were carried out,
one involving the use of only one nuclide, the other
involving the use of two. The procedures in the two
series were very similar.
TESTING MATERIALS AND APPARATUS
Termites.—C. brevis individuals are difficult to
identify precisely to instar above the third, so only
two categories of termite type were compared: large
nymphs (N) representing at least the fifth instar,
and small nymphs («) representing either the third
or the fourth instar. The weight of the large nymphs
averaged about three times that of the small. Stocks
from which the experimental termites were drawn
were collected from infested buildings at Tampa,
Florida, during the fall and winter of 1960 and kept
in their infested blocks of wood in a special chamber
until they were needed.
Constant Temperature Chamber.—Between sessions the experimental termites, as well as the termite stocks, were stored on shelves in a 3'X2'X2'
constant-temperature chamber set at 80° F. Large,
open pans of water kept the humidity high. These
conditions were adequate for keeping the termites
healthy in the laboratory.
Termitaries.—Housing and feeding of the experimental termites during the course of the experiments
were accomplished through the use of small wooden
cups made of balsa wood. Each was J4 inch in diameter, 1 inch tall, with walls about \{§ inch in
thickness, and with a floor % inch thick. Each
weighed about 200 milligrams. A termitary fitted
exactly into a 1-dram shell vial which was ^2 inch
in diameter and 2 inches tall. A few of the termitaries were made radioactive by filling them, as they
sat in their vials, with a water solution of a nuclide.
The water was evaporated away leaving radioactive,
dry termitaries. The radioactive termitaries were
capped with plastic circles cut to fit as lids and
swivelhinged by means of an insect pin. The nonradioactive termitaries were capped with corks from
which insect pins protruded for ease in removing a
termitary from its vial.
Nuclides.—Strontium-85 in the form of Sr^C^
was used in both Series 1 and Series 2. It had been
used in the earlier experiment and had appeared to
be satisfactory. This nuclide emits a 0.513 Mev
gamma ray with a half-life of 65 days. Cobalt-57 in
the form of Co57Cl2 was chosen as the second nuclide
in Series 2. It also is a gamma emitter and its
[Vol. 56
characteristic radiation is 0.123 Mev, sufficiently different from that of Sr85 for the two nuclides to be
distinguished and analyzed separately in measurements. Its half-life is 270 days. The nuclide preparation in each case was carrier-free.
The original dosages of the termitaries varied
between 20 and 40 microcuries per termitary. As a
given termitary decreased in radioactivity through
nuclide decay it was "recharged" by the addition of
more of the radioactive solution. Since for a given
nuclide one*termitary was used throughout a particular experimental session, and since each session was
a complete unit in which feeding comparisons were
made, these differences in degree of radioactivity
were not significant in making interpretations.
Radiation Detection Instruments.—Measurements
of radioactivity were made by means of a well-type
scintillation counter, with a l%X2}4-inch crystal,
connected to a single-channel pulse-height analyzer.
This was connected in turn with a decade sealer. All
counts were made using a 10-volt window width
and with the photomultiplier voltage adjusted so
that a 61.2-volt base setting gave maximum count
rate for total absorption of 0.662 Mev gamma rays
from a Cs137 source. Sr.85 was counted at a base setting of 46.5 volts, registering absorptions between
0.465 and 0.565 Mev. Co57 was counted at 9-volt
base setting, registering absorptions between 0.09
and 0.19 Mev. These base settings were selected
for peak count rates on the two activities. An automatic timer was used for presetting counting
intervals.
Background and Standard Samples.—The usual
counting time in the scintillation well was 10 minutes
per sample. At the beginning of each experimental
session and after approximately every 10 samples,
a background vial and a standard sample were
counted for radioactivity. These readings were used
in correcting the data later for background radiation,
for nuclide decay, and for possible machine fluctuations.
EXPERIMENTAL PROCEDURE
Series 1.—The first series of tests consisted of
five experimental sessions, each covering a period of
1 week and each composed of three stages: Stage A,
Stage B, and Stage C.
At Stage A, 24 large nymphs picked for their
similarity in size and development, and 24 small
nymphs, similarly selected, were removed from the
laboratory stock and weighed in groups of six of a
kind. Six N's and six n's were then placed together
in one Sr85 termitary to begin their roles as future
donors of radioactivity. The remaining termites
were placed in three nonradioactive termitaries, six
N's and six n's to each. They were to be the future
recipients. The four termitaries, each in its vial,
were returned to the constant-temperature chamber
and left undisturbed for 5 days.
Stage B followed 5 days after Stage A. The six N
and six n donors, now radioactive from feeding with-
1963]
MCMAHAX : TERMITE FEEDING RELATIONSHIPS
in the Sr"5 termitary, were placed separately in clean
vials, and their radioactivity was individually measured and recorded. The four most radioactive N's
and the four most radioactive n's were used in the
final part of the test. One donor was placed in each
of eight nonradioactive termitaries along with three
recipients. The final combination in a given termitary consisted of two Ar's and two n's representing
one donor and three recipients. (The terms "donor"
and "recipient" are used for convenience in distinguishing originally radioactive from nonradioactive
nymphs. The "donor" could presumably feed from
the "recipient" as well.) Care was taken in selecting
the four inhabitants so that no two had been together during the 5 days following Stage A. This
was to prevent the possibility of feeding relationships
based solely on familiarity of donor and recipient.
The eight termitaries were returned to the constanttemperature chamber and left undisturbed for 2
more days.
At Stage C (2 days after Stage B) the eight
termitaries were opened in turn and the radioactivity
of each nymph in terms of counts per minute was
measured individually. These data were those used
in making comparisons of relative amounts of radioactivity transferred from donor types to recipient
types. Other data collected at Stage C included
counts of radioactivity of pellets present and counts
of the empty termitary. These permitted an accounting for all radioactivity introduced into the termitary originally by the donor at Stage B.
Scries 2.—The second series of tests consisted of
10 sessions and involved two nuclides instead of one.
The general procedure was very similar to that of
Series 1. An exception was the placing of a pair of
supplementary reproductives in each termitary at
Stage A along with the experimental termites. Their
presence during the 5 days between Stages A and
H forestalled molting by the older nymphs. (When
nymphs are isolated from reproductives, a pair usually proceeds to go into a molting phase preparatory
to becoming supplementary reproductives, a process
that interrupts feeding behavior.) In general the
same supplementary pairs were used in all 10 experimental sessions. Another difference in Stage A
of Series 2 was the fact that only three iV's and
three n's were placed in each of the radioactive
termitaries (one a Sr*3 termitary, the other a Co67
termitary) to become donors, and only two N's and
two n's were placed in each of the three nonradioactive termitaries to serve as future recipients.
Procedures at Stages B and C were approximately
the same as for Series 1. At Stage B only four nonradioactive termitaries were set up with donors and
recipients. Two contained a large nymph as Srfir>
donor and a small nymph as Co57 donor, while in the
other two the small nymph was the Sr^" donor and
the large nymph had the Co57. Recipients in each
termitary consisted of one N and one n. At Stage C
each termite was measured twice for radioactivity,
once at the Sr85 setting, and once at the Co57 setting.
77
All the data have been corrected for background
radiation, for nuclide decay, and for machine fluctuations, and each count at Stage C in Series 2 has
also been corrected for the effect of the other nuclide.
RESULTS
Feeding Relationships.—In the analyses for food
transfer relationships between N and n termites, data
were included only from termitaries in which all
four inhabitants were alive and lively at Stage C.
This procedure resulted in a total of 39 termitary
units from Series 1, and 28 from Series 2.
Table 1 gives the results of both series, with Srs"
and Co57 data presented separately. The amounts of
radioactivity acquired by N and by n recipients when
paired with N and n donors are given first as average counts per minute per nymph, and then as average counts per minute per milligram of body weight.
The table indicates that large recipients acquired
more total radioactivity than did small recipients,
regardless of donor type, and a larger total amount
of radioactivity was acquired from large than from
small donors, regardless of recipient type. These
results are in line with expectation, for gut capacity
and feeding rate of N should be greater than those
of n. In order to make a more fruitful analysis of
feeding relationships, size of termite should be taken
into consideration.
An attempt was made to clarify the relationship
between termite size and acquisition of radioactivity
by carrying out the following experiment. Thirteen
termites were confined together in a Sr85 termitary.
Five were large nymphs, averaging 6.16 nig, in
weight, five were small nymphs, averaging 3.20 nig.,
one was a soldier weighing 4.50 mg., and two were
supplementary reproductives averaging 4.15 mg.
Each individual termite was identifiable, and each
was removed from the termitary once a day and
measured for radioactivity. At the end of 20 days
the survivors were placed in a nonradioactive termitary where they remained for 13 days, their individual
radioactivity again being measured daily. Only 10 of
the original group survived to the end of the experiment (a total of 33 days), and two of these survivors
molted during the period. This left only eight active
and nonmolted termites whose feeding rates might
be expected to be normal.
Figure 1 is a graph showing the average amounts
of radioactivity exhibited by the various termite
types day by day. It also shows the average amount
lost per pellet through elimination. All the figures
have been corrected for background radiation, nuclide
decay, and instrument fluctuations.
Differences in feeding ability (rate and capacity)
are reflected in the graph. N's had acquired considerably more radioactivity at every counting time
than had n's, which in turn had acquired considerably
more than the soldier and the reproductives. The
two latter types are dependent on colony mates for
food, never feeding directly on wood themselves.
Their gut capacities are known to be less than those
78
[Vol. 56
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
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DAYS IN RADIOACTIVE TERMITARY
20
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8
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10
12
14
DAYS IN NONRADIOACTIVE TERMITARY
FIG. 1.—Average daily gain and loss of radioactivity (Sr55) by different types of termites kept first in a
radioactive termitary and then in a nonradioactive one. Solid circles represent three large nymphs; half-black
circles, two small nymphs; triangles, a male and a female supplementary reproductive; squares, a soldier; dotted
line, pellets. The figures on the ordinate represent thousand counts per minute for all except the pellet data.
In this case the ordinate figures represent hundred counts per minute.
of nymphs of comparable weight (Holmgren 1909;
Katzin and Kirby 1939; McMahan 1960).
When the data of figure 1 are taken in conjunction
with those from similar tests the conclusion seems
warranted that, other things being equal, weight of
nymph is directly correlated with amount of radioactivity acquired in a radioactive termitary, and that
a nymph weighing three times as much as another,
for example, will acquire about three times as much
radioactivity. In table 1, therefore, the cpm/mg
figures are the more meaningful data from which
to make comparisons of feeding relationships between
the large and the small nymphs.
The results for the Sr83 data alone show that, per
unit weight, iV and n recipients were almost equal
in their acquisition of radioactivity from a given type
of donor. In both cases, however, more radioactivity
was acquired from N than from n donors.
The Co57 data are less uniform. They show that
n recipients acquired more radioactivity from iV
donors than did iV recipients, while the opposite was
true when the donor was a small nymph. There
appears to be no logical reason for supposing that
termite feeding behavior should be different when
the nuclide is changed. The differences are probably
due to chance variation, or to some unknown and
uncontrolled factor that differed in the two situations.
Table 1 indicates that there is no striking pattern
of food exchange dependent on the two general sizes
of nymphs used, although there is some evidence that
large nymphs are favored as donors. Another way
to test the hypothesis that on the average N and n
recipients fed equally from iV and n donors is to compare the number of times the iV recipient(s) in a termitary acquired more radioactivity (cpm/mg) than
the n recipient(s) with the number of times it acquired less. When N was the donor these figures
were 23 to 25 and when n was the donor, they were
M C M A H A N : TERMITE FEEDING
1963]
79
RELATIONSHIPS
Table 1.—Amounts of radioactivity, expressed as counts per minute (cpm), acquired by large (Ar) and by small
(>i) recipients from large (A') and from small (») donors.
I .arge
Donors
Avg. cpm
\vs
Scries and
nuclide
I -x"-
(Sr1*)
(Sr1sr>)
20
15
35
13
I1)
13
32
15
1
2
1+2 (Sr *)
2
(Co"")
1
(Si- 1 *)
2 (Srsr')
1+2 (Sr s ")
2 (Co w )
weight
Size (rag.)
A'
X
X
X
)!
n
n
ii
7.34
6.42
6.95
6.58
2.41
2.31
2.37
2.31
nymph
per
mg.
6,017
6,891
6,392
59,974
2,198
1,988
2,113
44,064
820
1,073
920
9,115
912
861
892
19,075
per
23 to 24. It is obvious that these results indicate no
significant differences in amounts of radioactivity
transferred in the different feeding combinations.
Routes of Radioactivity Loss.—Recipient feeding
was not the only way in which donors lost radioactivity. Other routes were via pellets and via
plaster, the latter an anal extrusion of liquid hindgut
material used by the termites to seal cracks and joints
in the termitary. Table 2 compares the amounts of
radioactivity lost by these routes. Because of unequal
donor radioactivity the figures are given as percentages. Each termitary unit was evaluated in
terms of percentage of original donor counts per
minute (at Stage I») that was lost by Stage C to
recipients, pellets, and plaster (plaster counts were
obtained by counting empty termitaries). Percentages were then averaged to obtain the figures given
in table 2. Some data from Series 2, additional to
those shown in table 1, are included here, a few
cases ill which both donors were either A/'s or n's.
X and n donors retained at Stage C comparable
percentages of their original radioactivity. The percentages lost to pellets by the two types were also
about the same. Differences in amounts lost to
plaster are probably not significant because a few
termitaries only were responsible for them. Small
donors consistently lost nearly twice as great a perTable 2.—Percentage of donors' acquired radioactivity
lost via different routes in the 2 days following their
removal from termitaries where, for 5 days, they had
fed on radioactive wood.
Donors
Series
and
nuclide
5
1
(Si-* )
>
-2
(Sr>*)
(Sr^i
1
((V)
1
(Sr 1*)
> (Sr«)
2 (Si* 8 )
I (Co57)
11
h
c
No.
Size 8
20
20
40
18
19
18
37
20
.V
.V
X
X
11
u
n
II
ii T3
caj SiS
Percentage lost
—
Recipients Pellets
62.90
46.74
54.82
88.97
49.95
53.34
51.60
87.61
4.83
9.51
7.17
5.25
14.40
16.91
15.62
10.28
.V signifies large nymphs, ii small ones.
Vellets from 19 termitary units included.
l'ellets from 39 termitary units included.
29.57
36.28b
32.84=
6.80
28.50
29.54
29.01
2.52b
Plaster
Total
0.75
1.03
0.89
0.37
7.78
2.00
4.97
0.28
98.05
93.56
94.90
101.39
100.63
101.79
101.20
100.69
(X) recipients
Aver.
weight
No. (mg.)
20
15
35
13
38
26
64
30
7.23
6.42
6.89
6.58
7.44
6.58
7.09
6.42
Small 0 0 recipients
nymph
per
mg.
Avg. cpm
Avg.
per
weight per
No. (mg.) nymph mg.
180
367
260
946
117
93
108
1,578
25
57
38
144
16
14
15
246
40
30
70
26
19
13
32
15
Avg. cpm
per
2.84
2.31
2.61
2.31
2.08
2.31
2.17
2.36
54
147
94
652
25
64
41
450
19
()4
36
282
12
28
19
195
centage to recipients as did large donors. This is
understandable in view of the fact that n donors were
always paired with one n and two N recipients while
N donors were paired with one N and two n recipients. A/'s, it has been shown, acquired more total
radioactivity from their donors than did n's.
It will be noted that the percentage figures do not
add up exactly to 100%. Some of this discrepancy
is probably due to statistical variation, and some
probably to the fact that anal-plaster material if
deposited at the top of the termitary was outside the
most effective position for counting. The close approximations, however, are reassuring on the question of whether or not most of the radioactivity
present in the donor at Stage B was recovered at
Stage C.
S/'-Co"
Differences.—An incidental finding, one
not related to termite feeding behavior, concerned an
apparent difference in behavior within the termite of
the two nuclides used in Series 2. (The more efficient
counting of cobalt as compared with the strontium
should not have affected the comparisons to be
made.) Table 2 shows that Srs5 donors averaged a
loss of over 45% of their radioactivity during the
2 days between Stages B and C, while Co57 donors
lost less than 15% of theirs. These differences were
found to be consistent and indicate a difference in
metabolic usage, with strontium apparently being
considerably more inert. Amounts (percentage) of
radioactivity lost to recipients, however, did not
differ appreciably for the two nuclides, as table 2
shows. The big difference lay in the loss of SrK5
by way of pellets, and the lack of loss of Co"7 by
this route.
An attempt was made to locate the radioactivity
within the termite body by dissecting a number of
large and small nymphs, some labelled with Sr80,
some with Co57, and some with both nuclides. All
had been removed from access to radioactivity at
least 16 days prior to being dissected. Before dissection each intact termite was measured for radioactivity. The head was then removed and placed in
a vial. The rest of the termite was placed in a small
droplet of Ringer solution on a clean watch glass
80
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
under a dissecting microscope. Fine scissors and
insect pins were used to open the exoskeleton and
free the gut. The malpighian tubules were cut off
at their attachment to the gut and carefully placed on
a small square of paper which was transferred to a
vial. The gut was divided into three sections: the
fore- and midgut, the short section of the hindgut
to which the stumps of the malpighian tubules were
attached, and the rest of the hindgut. The three
sections were placed separately on small paper
squares in separate vials. The exoskeleton, exclusive
of the head, was placed in another vial. The droplet
of Ringer in which the dissection had been made
and which usually contained myriads of protozoa
released from the hindgut was then blotted on a bit
of paper and placed in still another vial. The vials
and their contents were then measured one by one
for radioactivity. Each sample was counted for 1
minute.
Table 3 shows average percentages of radioactivity
found in the various portions of the dissected termites for both Srs3 and Co57 measurements. N and n
termites showed very similar distributions of the two
nuclides, so their data were combined in the analyses.
Table 3 shows that most of the SrS3 was located in
the malpighian tubules and that most of the Co57 was
in the hindgut and the dissecting fluid. Failure of
the total percentages to reach 100% is probably due
both to statistical variation in counts and to a loss
of some of the radioactivity through adherence to
the watch glasses in which dissections were made.
Some of the SrS3 termites dissected were those
represented in figure 1. Shortly before they were
dissected they had been producing pellets that were
only slightly radioactive, individual pellets averaging
less than 1% of the termite's total radioactivity instead of the 10% to 30% average that characterized
pellets of termites that had more recent access to
radioactive wood. In other words these termites
were not expelling radioactivity to any great extent,
and their total counts at the time of dissection
represented atoms stored in some form in the body.
Table 3.—Localization of SrS5 and Co57 in different
parts of the termite, expressed as average percentages of
total radioactivity."
Average percentage of
Part tested
Head
Fore- and midgut
Hindgut section with stumps of
malpighian tubules
Malpighian tubules
Rest of hindgut
Fxoskeleton (except head)
Dissecting fluid
Other
Total
SrSB
Co57
1.17
0.96
1.11
1.28
2.40
58.90
2.46
8.69
14.50
5.10
90.78
3.73
8.55
30.80
6.21
44.75
0.05
96.43
• A total of 11 SrS5-labelled termites (S large, 6 small) and S
Co57-labelled termites (3 large, 2 small) are represented in the
analysis.
[Vol. 56
Figure 1 shows that loss of radioactivity was much
slower than its gain. Waterhouse (1951), using
histochemical methods, found evidence that in insects, including termites, strontium is stored as
excretory granules in the cytoplasm of the malpighian tubules and as such are not passed out of the
body. The present data support his findings.
In showing a tendency for the strontium to be
lost slowly the data do not appear to be in line
with those of Grosch and LaChance (1956) who,
working with Habrobracon females and Srsu, found
the biological half-life of the nuclide to be less than
1 day. Similarly, Crossley and Schnell (1961) found
that the biological half-life of Sr*3 for two species
of grasshopper was about 10 and 12 hours, respectively. The}' pointed out that their data, which indicated a decrease in elimination rate after a few
days, suggest the possibility that a "longer-component
elimination rate is present." In both of these studies
the biological half-life was determined following an
initial feeding only. There is evidence also from
the tests with C. brcvis (table 2) that radiostrontium
was lost at a more rapid rate, percentage-wise, following a short feeding period than was the case
after the termites had fed for several weeks on labelled wood. Deposition of strontium as excretory
granules in appreciable quantity probably takes a
few days.
The Co37 data are puzzling at first glance. If
the nuclide was concentrated, as it seemed to be,
in the hindgut why was it not passed out in pellets? And if it was not available for pellets why
was it available to recipients? The explanation may
be that the microorganisms of the hindgut concentrated the nuclide and held it there. Protozoa are
not passed out with fecal material, although they are
passed from one termite to another during proctodeal
feeding (Cleveland 1926).
It is known that microorganisms concentrate minerals, including radioisotopes. For example, certain
plankton selectively accumulate specific elements and
organic metabolites into their bodies from minute
amounts in water (Williams 1960). Provasoli
(1958) suggests that in order to obtain a sufficient
quantity of trace metals, these organisms have developed powerful methods of trapping and dissolving
them, and might therefore be supersensitive under
laboratory conditions. Slater (1957) has studied the
accumulation of cobalt in Tctrahymcna during growth
and found a steady uptake.
Studies of cobalt metabolism have indicated that
cobalt is required by ruminants but not by nonruminants (Becker et al. 1949; Hutner et al. 1950),
and it has been suggested that this need is concerned
primarily with biological processes in the rumen,
probably related to the microorganisms (Thompson
and Ellis 1947). Termites, like ruminants, digest cellulose with the aid of the microflora and fauna of
the digestive tract. The present study suggests a
comparable utilization of cobalt.
Strontium may also have been concentrated, but to
1963]
MCMAHAN : TERMITE FEEDING RELATIONSHIPS
a lesser extent, by the microorganisms in the present experiment.
Pellet Production.—Drywood termites, such as C.
brcvis, produce discrete fecal pellets of characteristic
form. The collection of pellets produced by the experimental termites during the 2 days between Stages
B and C permitted an estimate to be made of the
rate of pellet production. Pellets were usually classified as large (about 0.85x0.50 mm.), medium (about
0.60X0.33 mm.), and small (about 0.40x0.25 mm.).
Size of pellet did not appear to be correlated closely
with termite size. Number and condition of the
pellets appeared generally to be good indicators of
the state of termite health.
There were 67 termitary units included in the
analyses for table 1. They represented 268 termites,
half Ar's and half H'S. These termites produced a
total of 387 pellets (277 large, 35 medium, 76 small,
and 47 tiny) in 2 days for an average of 0.72 pellet
per termite per day. The tiny pellets were not at all
typical and were found in only 2 of the 67 termitaries
with no larger pellets present. If these two cases
are omitted as atypical there remain a total of 340
pellets for 520 "termite days," an average of 0.65
pellet per termite per day.
DISCUSSION
The technique of using radioisotopes as tracers
in studying intertermite feeding relationships involves
certain problems. Factors affecting feeding are
numerous and difficult to control and it is hard to
get homogeneous data with a given category. In the
present study, for example, variation in amounts of
radioactivity acquired by different *V recipients and
by different n recipients was as great as that between
Ar and n recipients, ranging from zero to several
thousand counts per minute. Donors of a single type
also varied widely in the amounts obtained through
feeding in radioactive termitaries. Termites differ
in the number of microorganisms in the hind gut. If
the microorganisms concentrated the nuclides, this
fact alone could have caused large differences in cpm
counts between individual termites. It could at least
partially explain the differences in uptake observed
between soldier and nymph or between reproductive
and nymph in figure 1.
Incomplete control of factors affecting acquisition
of radioactivity, then, made analyses and interpretations difficult. It is much easier to give qualitative
than quantitative answers. We can be certain that
both N and n termites served as donors for both N
and n recipients in these experiments, but it is more
difficult to decide whether differences in feeding patterns were or were not exhibited. The best interpretation appears to be that they were not. But even
though no apparent feeding patterns based on the
two general sizes of termites tested were found, such
patterns might have been shown to exist if instars
had been identified precisely and tested separately.
Similar studies for caste and other categories could
be carried out.
81
A thorough investigation into the possibility of
patterns of food exchange might lead to a clarification of mechanisms underlying caste differentiation.
The regulation of soldier production, for example,
appears to be brought about, at least to some extent,
through a direct inhibiting action of soldiers already
in the colony. This may involve a transfer of pheromones (Karlson and Liischer 1959) or perhaps an
inter-individual sensory stimulation acting through
the central nervous system on the humeral system
(Karlson and Butenandt 1959). The regulation of
soldier production by existing soldiers does not
answer the question of what stimulates the appearance of the first soldier in the incipient colony or
explain why one nymph and not another becomes
that soldier. Weesner (1960) has suggested that a
positive environmental effect must be involved as
well as a negative one. She has postulated a special
relationship, possibly involving feeding, between two
nymphs at a certain stage in development that results
in one becoming the first soldier (Weesner 1956).
Liischer (1958, 1960) has reported that implantation
of active corpora allata will cause nymphs of Kalotermes flavicollis to develop into soldiers. He thinks
it likely that in normal soldier development nutritional factors are involved in the activation of the
corpora allata. A clue to these nutritional factors
might be sought in studies of food exchange relationships.
Such studies might also bring to light a possible
division of labor within a caste or between nymphs
of different ages. This type of specialization has
not been observed in termites to the extent to which
it has been found in bees (Ribbands 1953; Free
1957) and in wasps (Pardi 1948), although Kalshoven (1958) has reported it.
In spite of the difficulties inherent in the use of
radioisotopes for studying termite food exchanges,
the technique has much to recommend it. It permits
the following of these termite activities under relatively natural conditions of temperature, light, and
humidity. With improved control of factors causing
variation in the acquisition of radioactivity, more
homogeneous data may be expected. The present
investigation is only a beginning.
ACKNOWLEDGMENTS
Most of the work reported here was carried out
at the University of Chicago during 1960-61 while
the author was a Gladys Murphy Graham AAUW
Fellow. The encouragement and help of Dr. Alfred
E. Emerson and Dr. H. Burr Steinbach are gratefully acknowledged. Several other persons made
indispensable contributions to the research in the
form of a continued termite supply. They include
Mr. C. H. McMahan, the R. N. Campany family,
Mr. Clyde Reid, Mr. Bernard Kolkana and Mr.
Wally Hough of Orkin Exterminating Company,
Tampa, Florida; and Mr. Ed Coates. Earlier work
carried out at the University of Hawaii during 1959
and 1960 was done in connection with National
82
ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA
Science Foundation Grant No. G9581 awarded to
Dr. L. D. Tuthill. I also greatly appreciate the
comments of Dr. Donald J. Fluke, who has read the
manuscript.
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Uranotaenia gerdae, a New Species of the tibialis Group, from West New Guinea
(Diptera: Culicidae)1
R. SLOOFF
Division of Malariology, Department of Public Health
Hollandia, West New Guinea
ABSTRACT
This new species is described from material collected tibialis group. Its relations with the other species of
in Sorong, West New Guinea. The larval stage and the group are discussed briefly. The key of King and
adults of both sexes are known; the pupal siphon is Hoogstraal for males of New Guinea species is redescribed from a late fourth-instar larva. The foreleg produced in completed form,
ornamentation of the male places this species in the
The tibialis group of the genus Uranotaenia is
comprised of a number of species which, like U.
tibialis, have a peculiarly shaped appendage on the
tip of the male fore tibia, consisting of a tuft of hairs,
sometimes mixed with scales or bristles. King and
Hoogstraal (1947) were the first to describe species
1
Sponsored by Alan Stone; accepted for publication January
2, 1962.
of the group from. New Guinea. The characters of
the male foreleg, such as the shape of the tibial
appendage, the presence or absence of a fringe on
tarsal 2, and the relative sizes of femur, tibia, and
tarsus, are of the utmost importance in distinguishing
species. The male terminalia, however, do not show
specific structures. Females and larvae also appear
to be very much alike. As regards other characters,
the species fall well within Section A 1 of the genus