Physiological Entomology (2000) 25, 17-26
DAWN
M.
OLSONl,
HENRY
FADAMIRO2
,JONATHANG.
LUNDGRENandGEORGEE.HEIMPEL
Departmentof Entomology. University of Minnesota,St. Paul,U.S.A.
Abstract. Lifetime patterns of carbohydrateand lipid metabolismwere compared
in starved and sucrose-fed adults of the parasitoid Macrocentrus grandii
(Goidanich) (Hymenoptera:Braconidae).As expected,sucrose-fedindividuals lived
longer than did starved individuals. Macrocentrus grandii males and females
eclosed with levels of simple storagesugars (presumablyprimarily trehalose)and
glycogen that were below maximum levels recorded from sucrose-fedparasitoids.
Both of these nutrients dropped to very low levels in starved individuals within
4 days post-emergence and were maintained at high levels in sucrose-fed
individuals throughout their lives. Lipid reserves at emergencerepresentedthe
highest lipid levels for both sexesin the two diet treatments,with levels declining
over the lifetimes of males and females from both diet treatments. Our results
therefore suggestthat dietary sucroseis used to synthesizetrehaloseand glycogen,
but not lipids in M. grandii. Also, in contrast to the patterns observed for the
simple sugarsand glycogen,lipid levels in starved individuals did not drop below
levels observed in sugar-fed individuals. The average number of mature eggs
carried by females at emergencewas 33 and increasedto approximately 85 in
sucrose-fedand 130 in starvedfemales by the age of 5 d in the absenceof hosts.
The egg maturationrate was therefore higher in starvedthan in sugar-fedfemales.
Potentialexplanationsfor this unexpectedresult are discussed.
Key words. Anthrone tests, Braconidae, carbohydrate metabolism, lipid
metabolism,Macrocentrusgrandii, parasitoid,sugarfeeding.
Introduction
The adults of many insect speciesrequire sugar meals to
achieve maximum longevity (House,1974; Chapman,1982).
Parasitoidwaspsare especiallysensitiveto sugar deprivation
as adults;the laboratorylifespanof manyparasitoidspeciesis
typically lessthan 5 days in the absenceof sugarbut exceeds2
to 3 weeks when sugarmeals areprovided (Hagen,1986; van
Lenteren et ai., 1987; Heimpel et ai., 1997; Quicke, 1997;
Olson& Andow, 1998).In the field, potentialsugarsourcesfor
Correspondence:
GeorgeE. Heimpel, Departmentof Entomology,
University of Minnesota,St. Paul, MN 55108,USA. Tel: + I 612624
3480/6257055;fax: +1 6126255299; e-mail: [email protected]
lCurrent address: Insect Biology & Population Management
ResearchLaboratory,USDA-ARS Tifton, GA 31793,U.S.A.
2Currentaddress:PlantPestSurveyandBiological Control Program,
MinnesotaDepartmentof Agriculture, St. Paul, MN 55107,U.S.A.
(!;)200() ~Iackwell Science Ltd
parasitoidsinclude nectarand homopteranhoneydew(Rogers,
1985; Hagen, 1986; Jervis et al., 1992, 1993; Evans, 1993;
Jervis & Kidd, 1996),which provide primarily the disaccharide
sucroseand its two monosaccharidecomponents,glucoseand
fructose (van Handel et al., 1972; Magnarelli, 1979; Harborne,
1988). These sugar meals supplement carbohydrate-based
resourcescarried over from immature feeding stagesand can
be usedimmediatelyto generateenergyfor metabolicpurposes
or storedfor later use by conversionto trehaloseand glycogen
(Friedman,1985;Rivero & Casas,1999).De novo production
of lipids from simple sugarshas beendocumentedfrom some
insectsas well, but is apparentlylessuniversalthan production
of trehalose or glycogen (Downer & Matthews, 1976; van
Handel, 1984).
Although it is known that insect parasitoidsutilize sugar
sourcesin the field (Hagen, 1986; Evans, 1993; Jervis et al.,
1993,1996;Jervis & Kidd, 1996),a detailedunderstandingof
the conditions under which sugaris used in the field has been
8 Dawn M. Olson et
hindered in part by a lack of the application of appropriate
methodologiesto parasitoids.By contrast,tools for the studyof
sugarfeeding and carbohydrateand lipid use basedon simple
biochemical assayshave beenused for decadeswith various
dipteran species in both the laboratory and the field (e.g.
Bidlingmayer & Hem, 1973; Magnarelli, 1979; Magnarelli &
Anderson,1981; van Handel, 1984; Yuval & Schlein, 1986;
van Handel & Day, 1988; Yuval et al., 1994; Warburg &
Yuval, 1996). One goal of this study is to develop these
techniquesfor parasitoids.
Here we use a series of biochemical assaysdevelopedby
van Handel(1985a, 1985b)to documentlifetime trajectoriesof
simple storage sugars, glycogen and lipids of starved and
sugar-fed adults of the parasitoid M. grandii (Goidanich)
(Hymenoptera:Braconidae)(also known as M. cingulum; see
van Achterberg & Haeselbarth,1983). In particular, our goals
are to quantify the differences between emergence and
maximum levels of nutrients under the two feeding regimes,
and to determineif M. grandii arecapableof lipogenesisfrom
sugarmeals.We alsocomparelifetime egg maturationpatterns
of sucrose-fedand starvedfemales in the absenceof hosts.
Materials
and Methods
Macrocentrusgrandii wasintroducedfrom Europeand Asia to
the United Statesin the 1920sas a biological control agentof
the Europeancom borer, Ostrinia nubiiaiis Hiibner (Baker et
ai., 1949; Edwards & Hopper, 1998). Female M. grandii
oviposit one or a few eggs into the haemocoelof secondto
fourth instar O. nubiiaiis and eachegg probablydivides into 610 larvae by polyembryony (Parker, 1931). The larvae feed
within the host body and emergewhile the host is in the fifth
instar. Mter a brief period of external feeding, they spin
cocoons in masses of between three and 50 individuals
adjacent to the carcass of the host (Parker, 1931). Adult
femalesdo not host feed and the maximum adult lifespan of
healthy sugar-fed M. grandii is approximately 3weeks
(Andreadis,1980; Siegel et ai., 1986; Orr & Pleasants,1996;
see below). Substantially lower lifespans occur in the
laboratory when wasps are infected by the microsporidian
Nosemapyrausta (Pailot) (Andreadis, 1980; Siegel et ai.,
1986)or deprivedof a sourceof sugar(Orr & Pleasants,1996).
Adult parasitoidsused in the assayscame from 92 broods,
57 of which had eclosedfrom diapausingO. nubiiaiis, which
had beencollectedas larvae from fields throughout12counties
of Minnesota between August and October 1997. The
remaining 35 broods came from a colony that had been
maintainedon O. nubiiaiis larvae for oneto four generationsat
the time of the experimentsat 27°C, LD 16: 8h and 75:!: 5%
RH (hostsmaintainedas describedby Leahy & Andow, 1994).
Brood composition was either all-male (26%), all-female
(52%) or mixed sex (22%)and rangedin size from threeto 48
eclosingadults. Upon emergence,one or two waspsfrom each
brood weretestedfor Nosemaspp. infection by slide-mounting
whole-insecthomogenatesin 50 fll of Ringer's saline solution,
and checking for Nosemaspores at 400X. Parasitoidswere
only used in experimentsif they developedas part of a brood
from which the sampledindividuals were free from Nosema
infection. Andreadis (1980) showed that Nosema pyrausta
could be detectedin all membersof infected broods.
Sugar mealsand survivorship
We comparedsurvivorshipof M. grandii malesandfemales
thatwereprovided sucroseand water,or wateronly. Individual
broods were divided in half within 3 h of emergenceand
randomlyassignedto treatmentsof eithersucroseand water,or
wateronly. For mixed-sexbroods,the malesand femaleswere
equally divided between each treatment. Parasitoids were
housedin groups of two waspsof the same sex within 10cm
diameterplastic Petridishes.Parasitoidsemergingfrom singlesex broods were thereforeunmatedand parasitoidsemerging
from mixed-sexbroodswere potentiallymatedto their siblings
(Parker, 1931). Water was provided by filling a 0.5-ml
microcentrifuge tube with distilled water and threading a
cotton string through a hole in the cap of the tube. The tubes
were refilled as needed (i.e. every 5-7 days). Sucrosewas
provided as a 50% solution in distilled waterand was smeared
on the inside of the Petri dish cover with a cotton-tipped
applicator. Petri disheswere checkedonce daily for survival.
To determinethe effect of size on the probability of survival,
the forewings of eachwaspwere slide-mountedand measured
to the nearest0.02mm. Measurementswere taken from the
outeredge of the anal cell to the outeredge of the tip of both
wings for mostparasitoidsand averaged.For severalwasps,a
singlewing was measuredtwice and thesemeasurements
were
averaged.A total of 124 femalesand 105 maleswas used for
the survivorship analysis, stemming collectively from 15
broods. Some winglength measurementswere lost, so that
winglengths were obtained for a total of 96 females and 76
males.The effects of the food treatment,the sex of the wasp,
winglength and their interactions on survivorshipwere tested
using Cox's proportionalhazard model (SAS Institute, 1995).
Sugar,glycogen and lipid assays
Parasitoidsused in the nutrient assayscamefrom 57 broods
that had eclosed from diapausing O. nubilalis larvae,and 20
laboratory-rearedbroods. Members of eachbrood were split
evenlyacrosstreatmentsand agelevels. Two waspsfrom each
brood were placed in a Petri dish with sucroseand water or
water only, as describedabove.A singleparasitoidwas chosen
randomly from eachPetri dish for the assay.Parasitoidswere
assayed daily from ages 1-7 days and every other day
thereafteruntil the age of 21 days in the sucrose-fedtreatment,
and daily from ages 0-6 days in the starvationtreatment. A
total of 10 femaleswas assayedper age treatment,exceptfor
the water-only treatment,where lower numberswere used for
the two oldest age groups becauseof low survival to these
ages. Between five and 10 males were used for each time
period for both diet treatments,with the exceptionof the oldest
age groups.The forewings of each insect were removedand
2000 Blackwell ScienceLtd, Physiological Entomology,25, 17-26
.
20
Sugarfeeding in a parasitoid wasp 19
measuredas described above immediately before nutrient
analyseswere carried out.
The presenceof eggsin femaleparasitoidscould potentially
complicate interpretation of the nutrient assaybecausethe
nutrients held in eggs are presumablyunavailable for adult
maintenance.Even if eggs are resorbed,oosorption probably
occurs only under some conditions and is likely to be
metabolically costly (Bell & Bohm, 1975). We therefore
report nutrient levels for females from which the eggs were
removed by dissection.Femaleswere dissectedon a microscope slide cover slip in 50 ~l of a 2% sodium sulphate
solution and their ovaries were removed. The number of
matureeggs presentat the time of dissection(the 'egg load')
wasrecorded.The ovariesweretransferredto 50 ~l of Ringer's
saline,slide-mountedand viewed at 100X. Eggs for which the
complete chorion was clearly visible were consideredmature
and counted.
Post-dissectionfemales were transferred singly to 1.5-ml
microcentrifugetubes. The cover-slip from which the dissections had beendone was washedinto the tubes with 450 ~l of
chloroform-methanol(1: 2) to recover as much material lost
during the dissectionas possible and females were crushed
with a plastic pestle. Males were placed singly in 1.5-rnl
microcentrifuge tubes with 50 ~l sodium sulphate,crushed
with a plastic pestle and 450 ~l of chloroform-methanol(1 : 2)
was usedto washthe pestle.The tubeswere thenvortexedand
centrifuged at 16000 g for 2 min. After centrifuging,200 ~l of
the supernatant was transfeued to a glass test tube
(12 mm X 75 mm) for the sugar assays and 200 ~l was
transfeued to a similar glass tube for the lipid assay.The
precipitate was left in the microcentrifuge tube for the
glycogen assay. All tubes were heated at 90°C until all
solutionwasevaporatedfrom the lipid and glycogentubesand
approximately50 ~l of solutionremainedin the sugartubes.
Glycogenassay.Anthrone reagent(1 ml), preparedas in van
Handel (1985a), was added to the tubes containing the
precipitate and heated at 90°C for 15min. The tubes were
cooled on ice, mixed and contents were placed in 1.5-ml
methacrylatecuvettes. The absorbanceat 625 nm was read
using a spectrophotometer.
Lipid assay.Sulphuric acid (40 ~l) was addedto the tubes
containing the lipid precipitateand heatedfor 2 min at 90°C.
The tubes were cooled on ice and 960 ~l of a vanillinphosphoricacid reagent(preparedas in van Handel, 1 985b)
2.5
e=
(B)
2.0
I£j
~
"-'
1.5
~
u
=
=
1.0
~
0
~
0.5
.c
.c
-<
0.0
10
0
20
30
40
50
~g Sugar
/.lg Sugar
(C)
(D)
4
e=
E
=
In
14')
M
~~
N
~
~
i!~
CJ .
0
~
.Q
2
~
u
=
=
=
of
3 r-
,g
~ 1
'"
t
-<
0
Q
,Q
~
-<
0
0
40
60
80
j.LgGlycogen
100
~
0
20
40
60
80
100
j.LgSoybean Oil
Fig. 1. Standardcurves for fructose,sucroseand glucoseabsorbanceusing the cold anthronetest (A), and hot anthronetests(B), glycogenusing
the hot anthronetest (C), and soybeanoil using the vanillin-phosphoricacid test (D). Bars are SEM (n = 3 for each data point) and are only
visible if their le~gth is greaterthan the diameterof the datapoint.
(!;)2000 Blackwell Science Ltd, Physiological Entomology, 25, 17-26
20
Dawn M. Olson et at.
was added. The solution in each tube was left to react for
30min at room temperature,mixed and transferredto 1.5-ml
cuvettes.The absorbanceat 525nm wasrecorded.
Fructose assay (cold anthrone test). Anthrone reagent
(950~l) was addedto the supernatantof the tubes containing
the sugars, mixed and left to react for 1.5h at room
temperature.The absorbanceat 625nm was recorded.
Total sugars (hot anthrone test). The solutions from the
fructose assaywere heatedfor 15min at 90°C, cooled on ice
and the absorbanceat 625nrn was recorded.
Sampleswere run in batchesof betweensix and 12 insects,
along with a single negativecontrol samplewithout an insect.
The absorbancevaluesobtained for the negative control were
subtractedfrom absorbancevaluesof eachof the membersof a
given batch of insects for eachtest.
Standard curves. Known amounts of glucose, fructose,
sucrose,glycogenand lipid solutions(1 mgiml) were prepared
as in van Handel (1985a, 1985b). Soybeanoil was used to
generatethe lipid curve and the sourceof glycogenwas rabbit
1.0
(A)
liver (Sigma, St. Louis, MO, U.S.A.). Glucose,fructose and
sucrosesolutionswere preparedin amountsof 1, 5, 10,20, 30,
40 and 50 ~g and brought to a total volume of 1 ml with
anthronereagent.Glycogenand lipid solutionswere prepared
in amountsof 1, 5,10,25,50,75 and 100~g and broughtto a
total volume of 1 ml with anthroneand vanillin reagentsfor
glycogen and lipid standards,respectively. Absorbancewas
read at 625nm for the sugarsand glycogenand at 525nm for
the lipids. Threereplicatesper samplelevel were preparedand
nutrient amounts were calculated from the resulting linear
regressionequations(Fig. 1).
To estimate the amount of sugars presentin the body of
individual parasitoids excluding the gut contents, we subtractedthe gut sugarsfrom the total sugarsdetectedby the hot
anthronetest. The cold anthronereadingrepresentshalf of the
sugarspresentin the gutbecauseit detectsonly fructose,which
representsone half of the sugar presentin the sucrosemeals
(Chapman, 1982; see Fig. la) and becausefructose is not
present in insect haemolymph(e.g. van Handel, 1984; see
below). Body sugar levels were therefore estimated by
subtractingtwo timesthe amount of fructose detectedby the
cold anthronetest from the sugarsdetectedby the hot anthrone
test.
0.8
Statistical analyses
0.6
0.4
~
.-=>
.-
c=
=
rIJ
0.2
0.0
5
10
15
20
25
30
.S
...
=
~
=
...
~
Proportionalhazardsmodelswere usedto test for effects of
sex, diet and winglength on survivorship.The effects of diet,
ageand winglength on absorbancevaluesfrom assaysof body
sugars,glycogenand lipids were tested separatelyfor males
and females by multiple regressionanalysis in which the
qualitative variable,diet, was codedasa binary variable (Neter
et at., 1990).The sametestwas usedfor the numberof matUre
eggs in females. Transformations were necessary for the
absorbanceand egg load values to stabilize variances with
respectto the diet treatment. Absorbancevalues associated
with body sugar level estimateswere square-roottransformed.
Absorbancevalues for the glycogen tests were transformed
using a Box-Cox procedure(SAS Institute, 1995)that yielded
the transformationy' = (yo.6-1)/0.56. An inverse square-root
transformationwas used on absorbancevalues from the lipid
assaysand on the egg load data.
Table 1. Proportional hazardsmodel testing for effects of the diet
treatment, sex, winglength and interactions of these variables on
survival of Macrocentrusgrandii.
Sourceof variation
Age (days)
Fig.2. Survivorship curves for (A) female and (B) male
Macrocentrus grandii provided sucrose and water or water only.
Median longevity= 17 and 3 days for 64 and 60 females in the
sucrose and control treatments,respectively. Median longevity=10
and 3 days for 45 and 60 males in the sucroseand water and control
treatments,respectively.
Diet
Sex
Winglength
Diet X Winglength
Sex X Winglength
Diet X Sex
Diet X Winglength X Sex
d.t.
x2
1.107
7.29
6.54
7.01
6.26
10.33
8.83
p
0.293
0.007
0.011
0.008
0.012
0.001
0.003
2000 Blackwell ScienceLtd, Physiological Entomology,25, 17-26
~
Sugarfeeding in a parasitoid wasp 21
Results
Survivorship
Sucrosemeals increasedthe longevity of both male and
female M. grandii (Fig. 2). A proportional hazards model
including diet, sex and the interaction of thesetwo variables
revealed significant effects of both sex and diet on longevity
(diet: r=230, P<O.OOOI;sex: X;2=14, P<O.OOI). While
sucrose-fedfemaleslived longer than sucrose-fedmales, sex
did not have a significant effect on the longevity of starved
parasitoids, leading to a significant sexX diet interaction
(x;2=29, P<O.OOOI).Femaleswere significantly larger than
males in both treatments(P < 0.0001),leading to a significant
interaction between sex and winglength in a more complete
model (TableI). Furthermore,the effect of parasitoid winglength on longevity was dependentupon both sex and diet,
leading to a significant three-wayinteractionamong diet, sex
(A)
and winglength,which obscuredthe direct effect of diet in the
model (Table 1). Winglength had a significantpositive effect
on longevity of sucrose-fed males (longevity= 25.2+ 10.8
winglength, 1=0.244, P=0.003; n=45), but no effect on
longevity in starvedmalesor femalesfrom both diet treatments
(P> 0.2 for all analyses).
Nutrient analyses
Fructose.Fructose amountswere estimated with the cold
anthronetestand representone-halfof the sugarpresentin the
gut, owing to the fact that sucrose is composed of equal
amounts of fructose and glucose. As expected, the cold
anthronetestsfailed to detectfructose within unfed M. grandii
and both males and females that were fed sucroseshowed
consistentlyhigh fructose levels throughout their adult lives
(Fig. 3). Fructose levels were more variable in male than
female parasitoids,but no consistenttrends in fructose levels
could be detectedin either femalesor males over time (linear
regressionof fructoselevels overtime for both sexes:P> 0.5).
12
1(1
!
o-~
'"",..
0
~
.
S..101;-1'~'VI~
~
~
~
2
~
bO
(8)
:1.
14
J-
6
00
1
0
s
[)
5
10
15
20
10
15
2[)
"-
12
10
lO
f
8
8
T
1010
-1,. 10r!
6
~~~
2
10
T
...\
.
I
I I III
I
1
'.--
r
ol~.!g~
J!'
.
2
10
10
.~
~
.,1
S
10
J$
.~,
Age (days)
Fig. 3. Amounts of fructose (mean :!: SEM) detected over the
lifespans of (A) female and (B) male Macrocentrus grandii that
were provided sucrose and water (8) and water only (0). Sample
sizesare 10 for each of the time periods for sucrose-fedfemales, 10
for time periods 0-5 for starved females, and 8 and 4 for starved
females aged 5 and 6, respectively. For males, sample sizes are
abovestandarderror bars.
1;)2000 Blackwell Science Ltd, Physiological Entomology, 25, 17-26
-
Age(days)
Fig.4. Estimated amounts of body sugars(mean :t SEM) detected
over the lifespansof (A) female and (B) male Macrocentrusgrandii
that were provided sucrose and water (8) and water only (0).
Samplesizesare as in Fig. 3.
03
Dawn M. Olson et al.
Table 2. Multiple regressionanalysistesting the effect of diet, age, the interaction betweendiet and age, and winglength on absorbancevalues
for estimatedbody sugars,glycogen and lipids of male and female Macrocentrus grandii, as well as the egg load of females. All analyseswere
done on transformedvaluesas describedin the text and the diet treatmentwas codedas a binary variable.
Females
d.f.
Males
MS
F
p
M~
3.7
21.9
27.4
6.5
<0.055
<0.0001
<0.0001
<0.012
0.02
0.17
0.14
0.31
10.3
67.3
<0.0001
<0.0001
<0.0001
<0.0001
3.1
4.6
10.5
0.76
3.7
0.81
2.2
F
p
Body sugars
Diet
Age
0.10
0.58
0.73
0.17
Diet X Age
Winglength
Glycogen
Diet
19.0
19.5
12.2
7.7
Age
Diet X Age
Winglength
69.2
43.1
27.1
0.7
0.41
5.6
0.02
0.03
0.002
4.7
7.2
14.7
6.4
7.0
16.0
0.008
0.002
<0.001
<0.001
Lipid
Diet
Age
Diet X Age
Winglength
Number of Eggs
Diet
Age
Diet X Age
Winglength
0.01
4.9
0.5
0.001
0.74
0.08
2.14
14.3
<0.9
<0.03
<0.47
<0.001
0.02
0.04
0.05
0.01
29.4
46.8
58.6
15.2
<0.0001
<0.0001
<0.0001
0.0001
2.1
0.15
10.3
<0.01
0.13
0.01
2.3
6.2
Table 3. Diet-specificresults of linear regressionanalysestesting for the effect of Macrocentrusgrandii winglength on untransfonnedvaluesof
fructose,body sugars,glycogen and lipids for both males and femalesas well as egg loads for females. Regressionparametersare only reported
for P<O.lO.
Females
Variable
Diet
Fructose
Sucrose
Control
Sucrose
Control
Sucrose
Control
Sucrose
Control
Sucrose
Control
Body sugars
Glycogen
Lipids
Eggs
Males
p
0.'
~o
0.04
-3.7
131
2.7
?
p
/30
0.004
0.56
0.06
0.01
0.05
<0.001
<0.01
<0.01
<0.01
1:11
0.' 02
0.13
0.' 05
0.08
O.12010808< 0.0001
0:
0.41
0:
<0.001
0.03
0:
O.12
<0.0001
O.06
0.05
-8.5
-68
-18.2
-33
-73.7
-99.0
Sucrose-fedfemale and male M. grandii carried an average
(:t SEM) of 5.9:t 0.3 and 4.6:t 0.3 ~g of fructose, respectively (ages pooled; t233=2.5, P=O.OI). A very weak but
significant positive relationship between winglength and
fructose levels was detected in females, but not in males
(Table3).
Body sugars.The meanestimated amount of body sugars
presentin female and male M. grandii upon emergencewas
6.8 :t 1.2~g (n = 10) and 6.6:t 1.3 ~g (n = 7) , respectively
3.3
35.4
0.08
9.2
0.08
14.3
40.1
50.4
0.16
0.11
0.17
-12.2
-5.4
-72.1
-66.5
-13.4
-42.8
5.5
2.8
36.2
23.7
7.4
18.2
(Fig.4). Body sugar levels then dropped rapidly over the
lifespan of starvedadults of both sexes,whereastheyincreased
over the lifespan of sucrose-fedfemales and declined very
slightly overthe lifespan of sucrose-fedmales(Fig. 4, Table2).
Therewas no significantrelationshipbetweenthe age of either
females or males and their winglengths in either of the diet
treatments (P > 0.1 for all sex/diet combinations). This
suggeststhat there was little, if any, effect of parasitoidsize
on survivorshipduring the courseof the experimentandmakes
({;)2000 Blackwell Science Ltd, Physiological Entomology, 25, 17-26
Sugarfeeding in a parasitoid wasp
(A)
(A)
4Or
30
20
II!
0
"0
os.
;J
00
:1.
0
5
10
15
0
20
5
Age(days)
Fig.5. Amounts of glycogen (mean :!: SEM) detected over the
lifespansof (A) female and (B) male M. grandii that were provided
sucroseand water (8) and water only (0). Samplesizes are as in
Fig. 3.
it unlikely that the effectsof parasitoidage on sugarlevels are
due to differencesin the size distributions of individuals in the
differentagegroups.The relationshipbetweenwinglengthand
body sugarswas significant and weakly positive for starved
parasitoidsof both sexesas well as for sucrose-fedmalesand
non-significantfor sucrose-fedfemales(Table3).
Glycogen.Glycogenlevels of emergingfemale and male M.
grandii were 34.6:t 4.3 ~g (n = 10)and 31.3 :t 6.0 ~g (n = 7),
respectively (Fig. 5). They then dropped rapidly over the
lifespanof both sexesin the starvationtreatmentand increased
to levels approximatelytwice the emergencelevels in sucrosefed femalesand males(Fig. 5). In sugar-fedfemales,glycogen
levels declined to emergencelevels by day 21, and secondorder polynomial (quadratic) regression showed that the
relationship between age and glycogen levels in sugar-fed
femaleswas significantlydomed(Fig. 5). Glycogenreservesof
starved M. grandii were depleted by day 5, which coincides
approximately to maximum longevity in the starvation
treatment(see Fig.2) and remained uniformly high over the
lifespan of sucrose-fedparasitoids.The multiple regression
analysisshowedthat diet, age, diet X age,and winglength all
significantly affected glycogenlevels of both sexes(Table2).
Q 2000 Blackwell Science Ltd, Physiological1!;ntomology, 25, 17-26
10
15
20
Age(days)
Fig.6. Amounts of lipids (mean:t SEM) detectedover the lifespans
of (A) female and (B) male M. grandii that were provided sucrose
and water (8) and water only (0). Samplesizesare as in Fig. 3.
140
120
]
100
gg
~
80
60
40
20
0
5
10
15
20
Age(days)
Fig. 7. Numbers of mature eggs (mean ::t:SEM) dissected from
female M. grandii that were provided sucroseand water (8) and
water only (0) over their lifetimes. Samplesizesareas in Fig.3(A).
The relationshipbetweenwinglengthand glycogenlevels was
significantly positive for sucrose-fedparasitoidsof both sexes
24 Dawn M. Olson et aI.
and for starved males,but non-significantfor starvedfemales
(Table3).
Lipids. The highestlipid levels in both male and female M.
grandii were detected in individuals that had just eclosed
(Fig. 6). Lipid levels then declined significantly over the
lifespanof both sexesin both diet treatments(Fig. 6, Table2).
There was no statistically significantdifference in lipid levels
due to the diet treatmentin either sex (Table 2) and although
the rate of lipid decline appearedto be greater in starved
individuals of both sexes(Fig. 6), the diet-age interactionwas
insignificant for both males and females (Table2). The
relationship between winglength and lipids was significant
and positive for parasitoids of both sexes in both diet
treatments(Table3).
Egg load. At emergence,M. grandii females carried an
average of 33.1:!: 4.4 (n = 10) mature eggs (Fig.7). The
maximum egg load for sucrose-fedfemales was 85.5:!: 8.0
(n= 10)and occurredon day 4, and the maximumegg load for
starvedfemales was l28.5:!: 13.1 (n=8) and occurred on day
5. Overall,egg loads of sucrose-fedfemaleswere significantly
lower than egg loads of starved females, and there was a
significant interaction betweendiet and age (Fig. 7, Table2).
Winglengthhad a significantpositive effect on the numberof
mature eggs of females that were fed sugar, but only a
marginally significanteffect on the egg load of starvedfemales
(Table3). There was some evidence for modest but highly
variableegg resorptionin the sugar-fedgroup betweenthe day
of maximumegg load and the last day of the study.Egg loads
droppedsignificantlybetweendays4 and 21 in the sucrose-fed
females(,.2=0.08, P<O.Ol, slope=- 1.3). The significanceof
this relationshipwas increasedslightly when winglength was
addedto the analysis.Becauseof the small numberof females
in the starvationtreatmentthat survived past5 days,a similar
analysiscould not be done for this treatment.
Discussion
One goal of this study was to develop analytical tools that
could be used with field-collected parasitoids to determine
whether individuals had recently fed on sugar and to
distinguish betweenindividuals that are starving and individuals that are relatively well-fed. We have demonstratedhere
that the techniques used for various dipteran species are
applicableto the parasitoidM. grandii. First, we showedthat
the cold anthronetest, which detectsthe nectarsugarfructose,
doesnot yield positiveresults with starvedparasitoids.Second,
we determinedthat substantialand significantdifferencesexist
betweenthe body sugarlevels and glycogenreservesof sugarfed comparedwith starvedM. grandii.
Macrocentrus grandii males and females emerged with
relatively high reservesof body sugars,glycogenand lipids.
Body sugarsand glycogenreservesdeclined rapidly in starved
individuals and were nearly depletedby the age of 4 days in
both malesand females.Maximum longevity in the starvation
treatmentwas approximately6 days for both sexes,suggesting
that deathmay be attributableto the depletionof either or both
of these nutrients. Adult M. grandii that were fed a 50%
LUUUtllaclcwell Science Ltd, Physiological Entomology, 25, 17-26
Sugarfeeding in a parasitoid wasp 25
reluctantto attribute the higher egg loads in the starvedgroup
to changesin the compositionof femalesas they aged.
An alternative explanation is that starved females may
investmore energyinto reproductionpreciselybecauseof the
perception of lower life expectancy. Similar behavioural
responses,in which the oviposition rate is increased under
conditions of lowered life expectancy,have beendocumented
for a numberof parasitoidspecies(Roitberg et ai., 1992,1993;
Visser et ai., 1992; Fletcher et ai., 1994; but see Heimpel &
Rosenheim,1995),despitethe fact that increasedreproductive
effort has been shownto lower life expectancyin parasitoids
and other taxa (Bell & Koufopanou, 1986; Ellers & van
Alphen, 1996). Increasedegg maturation by starvedfemales
may be a viable strategy to increase lifetime reproductive
successif insectsare eitherincapableof resorbingeggs,or egg
resorptiondoes not substantiallyincreaselifespan, and if the
metabolic costs of increasedegg maturationare slight or not
incurred early in life.
Our data suggestthat sugar-starvedfemales may be more
limited by sugarthan lipid reserves.If egg productionis cheap
in terms of sugar but costly in terms of lipids, then sugarstarvedfemales that are not limited by lipids may be able to
use those lipids to mature more eggs while incurring only
minimal costs in terms of survivorship. Such a strategymay
enhanceshort-termopportunitiesfor reproduction,especiallyif
a rich patchof hostsis encounteredby a female with a low life
expectancy.
Acknowledgements
We thank Owain Edwards,Keith Hopper, John Luhman and
Ken Ostlie for kindly supplyingus with M. grandii, and David
Andow for supplying us with O. nubilalis. For advice on the
manuscriptand/orhelpful discussion,we thank David Andow,
Jerome Casas, Jason Harmon, Ralph Holzenthal, Marlijn
Hoogendoom,Keith Hopper, Mark Jervis, Ana Rivero, Jay
Rosenheim, Nancy Schellhorn, Robert Wharton and an
anonymousreviewer. This researchwas funded in part by
United StatesDepartmentof Agriculture grantno. 9802906to
G.E.H. and by the University of Minnesota Agricultural
ExperimentStation.This is contributionno. 99117-0018 of the
University of MinnesotaAgricultural ExperimentStation.
References
Andreadis, T.G. (1980) Nosema pyrausta infection in Macrocentrus
grandii, a braconid parasite of the European corn borer, Ostrinia
nubilalis. Journal of Invertebrate Pathology, 35, 229-233.
Antolin, M.P. & Williams, R.L. (1989) Host feeding and egg production
in Muscidifurax zaraptor (Hymenoptera: Pteromalidae). Florida
Entomologist, 72, 129-134.
Baker, W.H., Bradley, W.G. & Clark, C.A. (1949) Biological Control
of the European Corn Borer in the United States. United States
Department of Agriculture Technical Bulletin no. 983, Washington,
DC.
Bell, G. & Koufopanou, V. (1986) The cost of reproduction. Oxford
Surveys in Evolutionary Biology (ed. by R. Dawkins and M. Ridley),
pp. 83-131. Oxford University Press, Oxford.
2000 Blackwell ScienceLtd, Physiological Entomology,25, 17-26
Bell, W.J. & Bohrn, M.K. (1975) Oosorption in insects. Biological
Reviews,50, 373-396.
Bidlingmayer, W.L. & Hem, D.G. (1973) Sugar feeding by Florida
mosquitoes.Mosquito News,33, 535-538.
Brown, J.J. & Chippendale,G.M. (1974) Migration of the monarch
butterfly, Danaus plexippus: energy sources. Journal of Insect
Physiology,20, 1117-1130.
Chapman,R.F. (1982) The Insects: Strncture and Function. Harvard
University Press,Cambridge,MA.
Collier, T.R. (1995) Host feeding, egg maturation, resorption and
longevity in the parasitoidAphytis melinus(Hymenoptera:aphelinidae). Annals of the EntomologicalSociety ofAmerica, 88, 206214.
Downer,R.G.H. & Matthews,J.R. (1976) Patternsof lipid distribution
in insects.American Zoologist,16, 733-745.
Edwards,O.R. & Hopper,K.R. (1998)Using superparasitism
by a stem
borer parasitoidto infer a hostrange.Ecological Entomology,24, 712.
Ellers, J. (1996) Fat and eggs: an alternativemethod to measurethe
trade-off between survival and reproductionin insect parasitoids.
NetherlandsJournal of Zoology,46, 227-235.
Ellers, J. & van Alphen, J.J.M. (1996) Life history evolution in
Asobara tabida: plasticity in allocation of fat reservesto survival
andreproduction.Journal ofEvolutionary Biology, 10,771-785.
Evans.E.W. (1993) Indirect interactionsamongphytophagousinsects:
aphids, honeydew and natural enemies. Individuals, Populations
and Patternsin Ecology(ed. by A. D. Watt, S. R. Leather,K. E. F.
Walters :jnd N. J. Mills), pp. 63-80. InterceptPress,Andover.
Fletcher,J.P.,Hughes,J.P. & Harvey,I.F. (1994) Life expectancyand
egg load affect oviposition decisions of a solitary parasitoid.
Proceedings ofthe RoyalSociety ofLondonSeriesB,258,163-167.
Friedman,S. (1985) Intermediarymetabolism.FundamentalsofInsect
Physiology(ed. by M. S. Blum), pp. 467-506. JohnWiley & Sons,
New York.
Godfray, H.C.J. (1994) Parasitoids: Behavioral and Evolutionary
Ecology. PrincetonUniversity Press,PrincetonNJ.
Hagen, K.S. (1986) Ecosystem analysis: plant cultivars (HPR),
entomophagousspecies and food supplements. Interactions of
Plant Resistanceand Parasitoidsand Predators ofInsects(ed. by
D. J. Boethel and R. D. Eikenbary),pp. 151-197. Ellis Horwood
Limited Press,West Sussex,U.K.
Harborne, J.B. (1988) Introduction to Ecological Biochemistry.
AcademicPress.London.
Heimpel,G.E. & Rosenheim,J.A. (1995)Dynamic host feedingby the
parasitoidAphytis melinus: the balancebetweencurrent and future
reproduction.Journal ofAnimal Ecology, 64, 153-167.
Heimpel, G.E., Rosenheim,J.A. & Kattari, D. (1997) Adult feeding
and lifetime reproductivesuccessin the parasitoidAphytis melinus.
EntomologiaExperimentaliset Applicata, 83, 305-315.
House,H.L. (1974)Nutrition. The Physiology of Insecta,Vol. V (ed.
by M. Rockstein),pp. 1-62. AcademicPress,New York.
Jacome,I., Aluja, M., Liedo, P. & Nestel,D. (1995) The influenceof
adult diet and age on lipid reserves in the tropical fruit fly
Anastrepha serpentina (Diptera: Tephritidae). Journal of Insect
Physiology,41, 1079-1086.
Jervis, M.A. & Kidd, N.A.C. (1986) Host-feeding strategies in
hymenopteranparasitoids.Biological Reviews,61, 395-434.
Jervis, M.A. & Kidd, N.A.C. (1996) Phytophagy. Insect Natural
Enemies.Practical Approachesto Their Studyand Evaluation(ed.
by M. JervisandN. Kidd), pp. 375-394. Chapman& Hall, London.
Jervis,M.A., Kidd, N.A.C. & Walton,M. (1992)A review of methods
for determiningdietaryrangein adultparasitoids.Entomophaga,
37,
565-574.
26 Dawn M. Olson et al.
Jervis, M.A., Kidd, N.A.C., Fitton, M.G., Huddleston,T. & Dawah,
H.A. (1993) Flower-visiting by hymenopteranparasitoids.Journal
ofNatural History, 27, 67-105.
Jervis, M.A., Kidd, N.A.C. & Heimpel, G.E. (1996) Parasitoidadult
feeding behaviour and biological control- a review. Biocontrol
Newsand Information, 17, IIN-26N.
Leahy, T.C. & Andow, D.A. (1994) Egg weight, fecundity, and
longevity are increased by adult feeding in Ostrinia nubilalis
(Lepidoptera:Pyralidae). Annals of the Entomological Society of
America, 87, 342-349.
Magnarelli,L.A. (1979) Diurnal nectar-feedingof Aedescantator and
A. sollicitans (Diptera: Culicidae). Environmental Entomology,8,
949-955.
Magnarelli, L.A. & Anderson,J.F. (f981) Sugar feeding by female
tabanids (Diptera: Tabanidae) and its relation to gonotrophic
activity. Journal ofMedical Entomology,18,429-433.
Nayar,J.K. & van Handel,E. (1971) The fuel for sustainedmosquito
flight. Journal ofInsect Physiology,17,471-481.
Nestel, D., Galun,R. & Friedman,S. (1985) Long-term regulation of
sucrose intake by the adult Mediterranean fruit fly, Ceratitis
capitata (Wiedemann).Journal ofInsect Physiology,31, 533-536.
Neter, J., Wasserman,W. & Kutner, M.H. (1990) Applied Linear
StatisticalModels.3rd edn. RichardD. Irwin Press.Homewood,IL.
Olson, D.M. & Andow, D.A. (1998) Larval crowding and adult
nutrition effects on longevity and fecundity of female
Trichogramma nubilale Ertle & Davis (Hymenoptera:
Trichogrammatidae).EnvironmentalEntomology,27, 508-514.
Orr, D.B. & Pleasants,
J.M. (1996)The potentialof nativeplant species
to enhancethe effectivenessof the Ostrinia nubilalis parasitoid
Macrocentrus grandii. Journal of the Kansas Entomological
Society,69, 133-143.
Parker, H.L. (1931) Macrocentrus gifuensis Ashmead. a
PolyembryonicBraconid Parasite in the European Corn Borer.
USDA TechnicalBulletin no. 230.
Quicke,D.L.J. (1997) Parasitic Wasps.Chapman& Hall. London.
Rivero,A. & Casas,J. (1999)Incorporatingphysiologyinto parasitoid
behavioural ecology: the allocation of nutritional resources.
Researcheson Population Ecology,41, 39-45.
Roitberg, B.D. (1989) The cost of reproduction in rosehip flies,
Rhagoletisbasiola: eggs are time. Evolutionary Ecology, 3, 183188.
Roitberg, B.D., Mangel, M., Lalonde, R.G., Roitberg, C.A., van
Alphen, J.J.M. & Vet, L.E.M. (1992) Seasonaldynamicsshifts in
patch exploitation by parasiticwasps.Behavioral Ecology,3, 156165.
Roitberg, B.D., SiTcom,J., Roitberg, C.A., van Alphen, J.J.M. &
Mangel,M. (1993) Life expectancyandreproduction.Nature,364,
108.
Rogers,C.E. (1985) Extrafloral nectar: entomologicalimplications.
Bulletin ofthe EntomologicalSociety ofAmerica, 31, 15-20.
SAS Institute (1995)JMP Statisticsand Graphics Guide,Version3.1.
SAS Institute, Cary, NC.
Siegel,J.P.,Maddox,J.V. & Ruesink,G.W. (1986) Impact of Nosema
pyrausta on a braconid, Macrocentrus grandii, in central lllinois.
Journal ofInvertebrate Pathology,47, 271-276.
Tatar,M. & Carey,J.R. (1995) Nutrition mediatesreproductivetradeoff with age-specific mortality in the beetle Callosobruchus
maculatus.Ecology,76, 2066-2073.
van Achterberg,C. & Haeselbarth,E. (1983) Revisionarynoteson the
European species of Macrocentrus Curtis sensu stricto.
Entomofauna,4, 37-60.
van Handel,E. (1984) Metabolismof nutrients in the adult mosquito.
Mosquito News,44, 573-579.
van Handel,E. (1985a)Rapid determinationof glycogenand sugarsin
mosquitoes.Journal oftheAmerican Mosquito Control Association,
1,299-301.
van Handel, E. (1985b) Rapid determination of total lipids in
mosquitoes. Journal of the American Mosquito Control
Association,1, 302-304.
van Handel,E. & Day,J.F. (1988)Assayof lipids, glycogenand sugars
in individual mosquitoes: correlations with wing length in filedcollectedAedesvexans.Journal ofthe American Mosquito Control
Association,4, 549-550.
van Handel, E., Haeger,J.S. & Hansen,C.W. (1972) The sugarsof
someFlorida nectars.AmericanJournal of Botany,59, 1030-1032.
van Lenteren,J.C.,van Vianen,A., Gast,H.F. & Kortenhoff,A. (1987)
The parasite-hostrelationship between Encarsia formosa Gahan
(Hymenoptera: Aphelinidae) and Trialeurodes vaporariorum
Westwood (Homoptera: Aleyrodidae). XVI: food effects on
oogenesis,life span and fecundity of Encarsiaformosa and other
hymenopterousparasites.Zeitschriftflir AngewandteEntomologie,
103,69-84.
Visser, M.E., van Alphen, J.J.M. & Hemerik, L. (1992) Adaptive
superparasitismand patch time allocationin solitaryparasitoids:an
ESSmodel. Journal ofAnimal Ecology,61, 93-101.
Warburg,M.S. & Yuval, B. (1996)Effects of diet and activity on lipid
levels of adult Mediterraneanfruit flies. Physiological Entomology,
21, 151-158.
Yuval, B. & Schlein,Y. (1986) Leischmaniasisin the JordanValley
III. Nocturnal activity of Phlebotomus papatasi (Diptera:
Psychodidae)in relation to nutrition and ovarian development.
Journal ofMedical Entomology,23, 411-415.
Yuval, B., Holliday-Hansen,M.L. & Washino, R.K. (1994) Energy
budgetof swarmingmosquitoes.Ecological Entomology,19,74-78.
Accepted 17 August 1999
:[;j2000 Blackwell Science Ltd, Physiological
Entomology, 25, 17-26