Seventy captive adult female wasps of the eumenid genera Ancistrocerus and Euodynerus were observed to feed on multiple prey items. It was shown experimentally that E. foraminatus females that fed on prey had significantly larger egg volumes than adult wasps deprived of prey

Chilcutt, Charles F

Cowan, David P

English

ValpoScholar

The Great Lakes Entomologist 
Volume 25 
Number 4 - Winter 1992 Number 4 - Winter 
1992 
Article 8 
October 1992 
Carnivory in Adult Female Eumenid Wasps (Hymenoptera: 
Vespidae: Eumeninae) and Its Effect on Egg Production 
Charles F. Chilcutt 
Western Michigan University 
David P. Cowan 
Western Michigan University 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
Chilcutt, Charles F. and Cowan, David P. 1992. "Carnivory in Adult Female Eumenid Wasps (Hymenoptera: 
Vespidae: Eumeninae) and Its Effect on Egg Production," The Great Lakes Entomologist, vol 25 (4) 
Available at: https://scholar.valpo.edu/tgle/vol25/iss4/8 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1992 THE GREAT LAKES ENTOMOLOGIST 297 
CARNIVORY IN ADULT FEMALE EUMENID WASPS (HYMENOPTERA: 

VESPIDAE: EUMENINAE) 
AND 
ITS EFFECT ON EGG PRODUCTION 

Charles F. Chiicutt1,2, and David P. Cowan1 
ABSTRACT 
Seventy captive adult female wasps of the eumenid genera Ancistrocerus 
and Euodynerus 
were observed 
to feed on multiple prey items. It was shown 
experimentally that E. foraminatus females that fed on prey had significanly 
larger egg volumes than adult wasps deprived of prey. 
Most 
wasp larvae feed on arthropod prey provided for 
them by their 
parents 
(Spradbery 1973), 
but the basic food of adult wasps is presumed to be 
carbohydrates obtained from the nectar of flowers or honeydew of homopter­
ous insects (Evans 1966a, 1966b; Spradbery 1973; Iwata 1976). Frequent 
observations of adult predatory wasps eating sugary solutions has led to the
assumption by many researchers, that wasps acquire enough protein as larvae 
so that as adults they do not need high protein food (Hunt 1991). Nectar 
contains but a limited amount of protein (Hunt et al. 1982) and the amount of 
pollen consumed by predatory vespids is too low to be important for nourish­
ment (Hunt et 
al. 1991). 
Feeding 
by adult wasps on prey ha been observed many times and Evans 
(1966b) divided these behaviors into 3 categories: (1) imbibing blood from the 
sting 
puncture; 
(2) malaxating prey, defined here as chewing prey then feeding 
on blood from the wound before provisioning it for the young; and (3) malaxat­
ing prey 
specifically for 
adults and not using it as provisions, referred to as 
hypermalaxation. Our observations are similar to hypermalaxation, but we 
observed entire prey being consumed including flesh, along with instances of 
hypermalaxation. 
Many families of parasitoid w ps are known to feed from puncture 
wounds (Askew 1971). Those families of wasps known to malaxate their prey 
include the parasitoid Bethylidae (Finlayson 1950) a d the predators, Pompili­
dae (Evans and West-Eberhard 1970), Sphecidae (Leclercq 1959), and the soli­
tary 
Vespidae (Eumeninae) (Malyshev 1968). Hypermalaxation 
has been 
described in the bethylids (Finlayson 1950), tiphiids (Burdick and Wasbauer 
1959), pompilids (Evans and Yoshimoto 1962), sphecids (Lin 1978), and eume­
nids (Rau 1945). 
Three main hypotheses have been proposed t  explain why adult wasps 
feed on prey: (1) a source of fluids (Lin 1978) especially during flower (nectar) 
scarcity (Evans and West-Eberhard 1970); (2) to quiet struggling prey (Le. 
Spradbery 1973); and (3) it has no function, but is a displacement activity 
IDepartment of Biological Sciences, Western Michigan University, Kalamazoo, MI 
4900~. 
Current address: 
Department of Entomology, University of Hawaii, 3050 Maile 
Way, Honolulu, HI 96822. 
1
Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: E
Published by ValpoScholar, 1992
298 THE GREAT LAKES ENTOMOLOGIST Vol. 25, No.4 
exhibited by confused wasps unable to nest (Huber 1961). A fourth possibility, 
that 
female 
predatory wasps require proteinacious p y for egg development 
(Spradbery 1973) has not been tested. Evans (1966a) stated that many sphecid 
wasps 
feed on 
prey only under special conditions, but there is little evidence 
that it 
occurs regularly. 
Hunt (1991) reiterated this generally accepted opinion 
by stating that reports 
of prey-feeding 
by adult wasps is "fragmented and 
largely anecdotal", d continues "that nectar, nectar-like liquids, and body 
fluids of prey or carrion are the typical, and nearly exclusive, sources of adult 
nourishment". Several workers have argued that adult wasps are not morpho­
logically adapted to eating solid food. Imms (1957) suggested that the mandi­
bles of adult wasps were adapted for nest building rather than for a trophic 
function, Spradbery (1973) believed that adult wasps are restricted to a liquid 
diet by the 
narrowing of 
the esophagus in the cervical region, and Hunt (1991) 
emphasized the distensible crop a d restrictive proventriculus. Because th  
prey 
of 
solitary wasps is usually widely scattered, frequent observations of 
predatory events 
in 
nature are unlikely and we believe that carnivory in preda­
tory wasps has 
been overlooked 
as a source of protein for ovarian develop­
ment. In this study we report on adult female carnivory in captive eumenid 
wasps and its 
relationship with 
egg development. 
MATERIALS AND METHODS 
A 
total of 71 adult female wasps of the eumenid genera Ancistrocerus and 
Euodynerus 
were observed 
nesting in captivity from 1989 to 1991. While 
nesting, all of these adult females were observed feeding on multiple prey 
items. To study the effects of adult female carnivory on ovarian development, 
20 females of Euodynerus foraminatus (Saussure) were maintained in one 
gallon jars (two wasps per jar). Each was provided with water and a honey 
solution (to replace the nectar they would normally obtain at flowers). All 
females were mated to control for possible effects on egg maturation found in 
other 
insect species (De Wilde 1964). 
One 
group of 10 females was given spruce budworm (Choristoneura fumi­
ferana Clemens) caterpillars and observed the first day to ensure that each 
consumed the prey. Following this, they were provided with an abundance of 
prey 
(more 
than they could eat). A second group of 10 females was not given 
caterpillars. Starting 3 days after the first caterpillars were provided, one 
wasp 
from each 
group was dissected daily for 10 days. The length and diam­
eter 
of 
the 2 largest eggs (one terminal oocyte from each of the paired ovaries) 
were measured using a dissecting microscope and ocular micrometer. Oocyte 
volume was approximated by multiplying the length by the square of the 
diameter (V=Ld2). Significance for all statistical tests was set at p:s;0.05. 
During dissection, the crop and ventriculus of each wasp as also dissected 
and 
examined for content. 
The head widths (an indicator of size in wasps) of 
the 
20 
E. foraminatus were m asured using a dissecting microscope a d ocular 
micrometer. 
RESULTS 
The 
average 
total egg volume (the 2 largest eggs) for the group given prey 
(0.809 mm3) was significantly greater than for the group denied prey (0.330 
mm3) (t=3.75,p<0.001). The average largest egg volume for the experimental 
group 
(0.520 
mm3) was significantly greater than for the control (0.255mm3) 
(t=3.32, p<0.005). The average smallest egg volume for the experimental 
2
The Great Lakes Entomologist, Vol. 25, No. 4 [1992], Art. 8
https://scholar.valpo.edu/tgle/vol25/iss4/8
1992 THE GREAT LAKES ENTOMOLOGIST 299 
group (0.289 mm3) was significantly greater than for the control (0.075mm3) 
(t=3.45, p <0.005). The average h ad width of the group fed on prey (3.28mm) 
and the group 
denied 
prey (3.25mm) were not significantly different (t=0.268, 
p >0.1). This was important, because Larrson (1990) and O'Neill (1985) found 
strong 
correlations between 
head size and egg size in sphecid wasps. 
All wasps fed on the sugar solutions provided, but none showed any 
interest 
in 
the cups containing pollen. The crops of dis ected wasps were 
found to bedistended with sugar solution. When we dissected wasp ventriculi, 
we found no fragments of prey, although the ventriculi did tak  on the darker 
color of p ey tissues after wasp feeding. 
We estimate that individual wasps ate from 6 to 18 caterpillars after being 
given 
access 
to prey. Due to difficulties of observation, it seems likely that the 
high end of the range is 
closest 
to the actual number of prey eaten. There was 
a distinct period before nesting began, when the wasps each ate approxi­
mately 
4 caterpillars. 
After nesting and provisioning began, however, all 
females were observed eating prey at vari us tim s which we could not corre­
late with any phase of the nesting 
cycle. 
When wasps were deprived of prey 
(twice, each time for one week) nest cavities were partitioned and closed with 
mud, but no eggs were found. Because eumenids oviposit before provisioning, 
cells with only eggs might be expected if the presence of prey were not needed 
to stimulate ovarian 
development 
(through feeding). 
Prey captured and 
fed 
upon by adult females were not always stung first. 
Individuals 
of 
E. foraminatus were more likely to chew through the prey's 
cervical area to kill it, and then devoure the rest of the prey without a strug­
gle. Feeding always began on the last abdominal segment and lasted from 2 to 
15 min. Larger caterpillars were often only partly eaten and discarded, while 
smaller prey were devoured leaving only the head capsule. While eating prey, a 
wasp 
holds 
the caterpillar by the abdomen with her forelegs and curls h r 
abdomen under the prey in a position similar to stinging.This position made t 
difficult to discern whether wasps were just holding p y or stinging it. 
Smaller prey were less likely to be stung because of difficulties involved in 
locating the 
normal 
sting region and the ease of subduing a small victim by 
biting 
it. 
DISCUSSION 
Our observations 
of prey-feeding 
by adult eumenids contradict the view 
that adult wasps 
feed 
to acquire fluids on ry days (Lin 1978). Our wasps were 
always provided with an ample supply of water, yet still fed on prey. The idea 
that adult 
feeding 
behavior is a response to flower nectar scarcity (Evans and 
West-Eberhard 
1970) 
is contradicted by our observations of distended crops 
(filled with sugar solution) found in females iss cted during the period we 
observed 
prey-feeding. 
This indicates that the absence of nectar is not what 
stimulates 
prey-feeding. 
Nor was there any indication that eating prey was a 
displacement activity 
exhibited 
by wasps in response to novel r confusing 
situations. 
Rather, 
it is a normal necessary activity associated with egg devel­
opment. Our results are 
in line 
with numerous studies of parasitoid Hymenop­
tera that 
require 
maturation feeding on hosts (prey) for full egg development 
(DeWilde 1964). Flanders (1942) explained that in many species of Hymenop­
tera larval nutrition 
is insufficient for 
egg development to proceed in the adult 
without further 
feeding, 
adding that these adult females habitually feed on 
the body 
fluids of 
their hosts prior to oviposition. Our measurements of eggs 
for wasps which did not feed on prey (some eggs almost as large as those of 
prey-fed wasps) indicate that vitellogenesis begins in eumenid females in the 
3
Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: E
Published by ValpoScholar, 1992
300 THE GREAT LAKES ENTOMOLOGIST Vol. 25, No.4 
absence of prey or protein sources other than those acquired as larvae. Prey­
feeding is essential to maturation of more than one egg (wasps not fed prey as 
adults had 
only one developing egg) 
and possibly even for maturation of the 
first 
egg. This condition is similar 
to that described by Flanders (1935) for the 
Pteromalidae and found in several dipteran species (Clements 1963). 
Until now research on the effects of prey-feeding on ovarian development 
had not 
been carried 
out for solitary predatory wasps. The many reports of 
prey-feeding (on the body fluids) by adult female Sphecidae (Evans 1966a), 
eumenids (Iwata 1953), and pompilids (Rau 1945) have not been correlated 
with ovarian development. It is likely that these many anecdotal reports of 
predatory 
solitary wasps feeding on 
prey are involved with egg maturation. It 
also seems likely that more intensive studies of predatory behavior will reveal 
prey feeding to be a regular part of female activities and not something 
brought 
on 
by adverse conditions (i.e lack of water). 
Total mastication of prey as we observed for eumenids has been observed 
for social species. Rau (1945) described workers of Polistes spp. thoroughly 
pulping caterpillar prey in their jaws so that it could be swallowed. Chapman 
(1963) found Vespula pennsylvanica (Saussure) feeding on swarming reproduc­
tive ants. Wasps were observed "dozens of times" capturing ants and landing 
to 
chew their prey, while no prey was seen 
to be carried back to the nest. 
Examinations of the ventriculi of 20 wasps failed to reveal any ant fragments, 
implying that only body fluids were ingested. Unlike the soft, thinly 
sclerotized lepidopterans fed on by eu~enids, the heavily sclerotized nt cuti­
cle would be difficult to digest. This, along with the need for adult wasps (with 
a narrowed esophagus) to finely chew their food, probably is related to why no 
fragments were found. Chapman (1963) described the wasps biting off the 
heads of their ant prey and "prefering" to feed on the abdomen rather than the 
thorax, behaviors we described earlier for E. foraminatus. This behavior has 
also been described by Ross (1983) for Vespula spp. which assume the same 
posture we described for solitary vespids feeding on prey, enclosing "the strug­
gling prey with the ventral surface of the gaster, the legs, and the 
mouthparts". Gillaspy (1979) gave descriptions of Polistes spp. returning to 
the nest 
with no 
apparent load with dissected crops containing a "thin gruel of 
protein food with recognizable insect parts". 
Among vespids, the transition from solitary to social life has also involved 
the 
transition from feeding larvae 
intact prey items to feeding young com­
pletely masticated prey meat. Our results indicate that the complete chewing 
of prey was likely well e tablished among the solitary ancestors (as a preadap­
tation) of the living social species. 
LITERATURE CITED 
Askew, R. R. 1971. Parasitic insects. American Elsevier Publishing Company, Inc., NY. 
pp. 136-137,152. 
Burdick, D. J., and M. S. Wasbauer. 1959. Biology of Methoca califomica Westwood. 
Wasmann J. BioI. 17:75-88. 
Chapman, J. A. 1963. Predation by Vespula wasps on hilltop swarms of winged ants. 
Ecology 44:766-767. 
Clements, A. N. 1963. The physiology of mosquitoes. The MacMillan Company, NY. pp. 
169-175. 
DeWilde, J. 1964. Reproduction. In: M. Rockstein (ed.). The physiology of Insecta. Vol. 
1. 
Academic Press, 
NY. pp. 10-58. 
Evans. 	
H. 
E. 1966a. The comparative ethology and evolution of the sand wasps. 
Harvard 
University Press, Cambridge, Mass. pp. 427-429. 
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__. 1966b. The behavior patterns of solitary wasps. Ann. Rev. Entomol. 
11:123-154. 
Evans, H. E., and M. J  West· Eberhard. 1970. The wasps. Univeristy of Michigan Press, 
Ann 
Arbor. 
p. 59. 
Evans, H. E., and C. M. Yoshimoto. 1962. The ecology and nesting behavior of the 
Pompilidae of the northeastern United States. Misc. Pub!. Entomol. Soc. Am. 
3:65-119. 
Finlayson, L. H. 1950. The biology of Cephalonomia waterstoni Gahan, a parasite of 
Laemophloeus. Bull. Entomol. Res. 41:79-97. 
Flanders, S. E. 1935. An apparent correlation between the feeding habits of certain 
pteromalids and the condition of their ovarian follicles. Ann. Entomol. Soc. Am. 
28:438-444. 
1942. Oosorption and ovulation in relation to oviposition in the parasitic Hyrne· 
noptera. Ann. Entomol. Soc. Am. 35:251-266. 
Gillaspy, J. E. 1979. Management of Polistes wasps for caterpillar predation. South· 
western Entomol. 4:334-352. 
Huber, A. 1961. Zur biologie von Mellinus aruensis L. Zool. Jahrb. (Syst.) 89:43-118. 
Hunt, J. 
H. 1991. Nourishment 
and the evolution of the social Vespidae. In: K.G. Ross, 
and 
R.W. 
Matthews (eds.). The social biology of wasps. Comstock Publishing Associ· 
ates, Ithaca, NY. pp. 426-450. 
Hunt, J. 
H., 
I. Baker, and H. G. Baker. 1982. Similarity of amino acids in nectar and 
larval saliva: the nutritional basis for trophallaxis in social wasps. Evolution 
36:1318-1322. 
Hunt. J. 
H., 
P. A. Brown, K. M. Sago, and J. K. Kerker. 1991. Vespid wasps at pollen 
(Hymenoptera: Vespidae). J. Kans. Entomo!. Soc. 64:127-130. 
Irnms, A. D. 1957. A general textbook of entomology. Methuen, London. p. 525. 
Iwata, K. 1953. Biology of Eumenes in Japan. Mushi 25:25-47. 
__
. 1976. Evolution of instinct: comparative ethology of Hymenoptera. Amerind, 
New Delhi. 535 pp. 
Larrson, F. 
K. 1990. Female body size relationships with fecundity and egg size in two 
solitary species of fossorial Hymenoptera (Colletidae and Sphecidae). Entomol. Gener. 
15:167-171. 
Leclercq, J. 1959. Une population de Mellinus arvensis L. d ns laquelle les fernelles 
chassent pour leur propre compte (Hym. Specidae Nyssoninae). Bull. Soc. Royale 
Sciences Liege 28:246-249. 
Lin, N. 1978. Sequential hypermalaxation in the digger wasp Diodontus franclemonti 
Krombein (Hymenoptera: Sphecidae). J Kans. EntomoL Soc. 51:235-238. 
Malyshev, S. I. 1968. Genesis of the Hymenoptera and the phases of their evolution. 
Methuen, London. pp. 182-185. 
O'Neill, K.M. 1985. Egg size, prey size. and sexual size dimorphism in digger wasps 
(Hymenoptera: Sphecidae). Can. J. Zool. 63: 2187-2193. 
Rau, P. 1945. The carnivorous habits of the adult wasp Odynerus dorsalis Fab. Bull. 
Brooklyn Entomol. Soc. 40:29-30. 
Ross, K. G. 1983. Studies of the oraging and feeding behavior of yellowjacket foun· 
dresses, Vespula (Paravespula) (Hymenoptera: Vespidae), in the laboratory. Ann. 
Entomol. Soc. Am. 76:903-912. 
Spradbery, J. P. 1973. Wasps: an account of the biology and natural history of solitary 
and social wasps. University of Washington Press, Seattle. pp. 43-44. 
5
Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: E
Published by ValpoScholar, 1992


Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: Eumeninae) and Its Effect on Egg Production

Valparaiso University

The Great Lakes Entomologist Volume 25 Number 4 - Winter 1992 Number 4 - Winter 1992 Article 8 October 1992 Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: Eumeninae) and Its Effect on Egg Production Charles F. Chilcutt Western Michigan University David P. Cowan Western Michigan University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation Chilcutt, Charles F. and Cowan, David P. 1992. "Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: Eumeninae) and Its Effect on Egg Production," The Great Lakes Entomologist, vol 25 (4) Available at: https://scholar.valpo.edu/tgle/vol25/iss4/8 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1992 THE GREAT LAKES ENTOMOLOGIST 297 CARNIVORY IN ADULT FEMALE EUMENID WASPS (HYMENOPTERA: VESPIDAE: EUMENINAE) AND ITS EFFECT ON EGG PRODUCTION Charles F. Chiicutt1,2, and David P. Cowan1 ABSTRACT Seventy captive adult female wasps of the eumenid genera Ancistrocerus and Euodynerus were observed to feed on multiple prey items. It was shown experimentally that E. foraminatus females that fed on prey had significanly larger egg volumes than adult wasps deprived of prey. Most wasp larvae feed on arthropod prey provided for them by their parents (Spradbery 1973), but the basic food of adult wasps is presumed to be carbohydrates obtained from the nectar of flowers or honeydew of homopter­ous insects (Evans 1966a, 1966b; Spradbery 1973; Iwata 1976). Frequent observations of adult predatory wasps eating sugary solutions has led to theassumption by many researchers, that wasps acquire enough protein as larvae so that as adults they do not need high protein food (Hunt 1991). Nectar contains but a limited amount of protein (Hunt et al. 1982) and the amount of pollen consumed by predatory vespids is too low to be important for nourish­ment (Hunt et al. 1991). Feeding by adult wasps on prey ha been observed many times and Evans (1966b) divided these behaviors into 3 categories: (1) imbibing blood from the sting puncture; (2) malaxating prey, defined here as chewing prey then feeding on blood from the wound before provisioning it for the young; and (3) malaxat­ing prey specifically for adults and not using it as provisions, referred to as hypermalaxation. Our observations are similar to hypermalaxation, but we observed entire prey being consumed including flesh, along with instances of hypermalaxation. Many families of parasitoid w ps are known to feed from puncture wounds (Askew 1971). Those families of wasps known to malaxate their prey include the parasitoid Bethylidae (Finlayson 1950) a d the predators, Pompili­dae (Evans and West-Eberhard 1970), Sphecidae (Leclercq 1959), and the soli­tary Vespidae (Eumeninae) (Malyshev 1968). Hypermalaxation has been described in the bethylids (Finlayson 1950), tiphiids (Burdick and Wasbauer 1959), pompilids (Evans and Yoshimoto 1962), sphecids (Lin 1978), and eume­nids (Rau 1945). Three main hypotheses have been proposed t  explain why adult wasps feed on prey: (1) a source of fluids (Lin 1978) especially during flower (nectar) scarcity (Evans and West-Eberhard 1970); (2) to quiet struggling prey (Le. Spradbery 1973); and (3) it has no function, but is a displacement activity IDepartment of Biological Sciences, Western Michigan University, Kalamazoo, MI 4900~. Current address: Department of Entomology, University of Hawaii, 3050 Maile Way, Honolulu, HI 96822. 1Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: EPublished by ValpoScholar, 1992298 THE GREAT LAKES ENTOMOLOGIST Vol. 25, No.4 exhibited by confused wasps unable to nest (Huber 1961). A fourth possibility, that female predatory wasps require proteinacious p y for egg development (Spradbery 1973) has not been tested. Evans (1966a) stated that many sphecid wasps feed on prey only under special conditions, but there is little evidence that it occurs regularly. Hunt (1991) reiterated this generally accepted opinion by stating that reports of prey-feeding by adult wasps is "fragmented and largely anecdotal", d continues "that nectar, nectar-like liquids, and body fluids of prey or carrion are the typical, and nearly exclusive, sources of adult nourishment". Several workers have argued that adult wasps are not morpho­logically adapted to eating solid food. Imms (1957) suggested that the mandi­bles of adult wasps were adapted for nest building rather than for a trophic function, Spradbery (1973) believed that adult wasps are restricted to a liquid diet by the narrowing of the esophagus in the cervical region, and Hunt (1991) emphasized the distensible crop a d restrictive proventriculus. Because th  prey of solitary wasps is usually widely scattered, frequent observations of predatory events in nature are unlikely and we believe that carnivory in preda­tory wasps has been overlooked as a source of protein for ovarian develop­ment. In this study we report on adult female carnivory in captive eumenid wasps and its relationship with egg development. MATERIALS AND METHODS A total of 71 adult female wasps of the eumenid genera Ancistrocerus and Euodynerus were observed nesting in captivity from 1989 to 1991. While nesting, all of these adult females were observed feeding on multiple prey items. To study the effects of adult female carnivory on ovarian development, 20 females of Euodynerus foraminatus (Saussure) were maintained in one gallon jars (two wasps per jar). Each was provided with water and a honey solution (to replace the nectar they would normally obtain at flowers). All females were mated to control for possible effects on egg maturation found in other insect species (De Wilde 1964). One group of 10 females was given spruce budworm (Choristoneura fumi­ferana Clemens) caterpillars and observed the first day to ensure that each consumed the prey. Following this, they were provided with an abundance of prey (more than they could eat). A second group of 10 females was not given caterpillars. Starting 3 days after the first caterpillars were provided, one wasp from each group was dissected daily for 10 days. The length and diam­eter of the 2 largest eggs (one terminal oocyte from each of the paired ovaries) were measured using a dissecting microscope and ocular micrometer. Oocyte volume was approximated by multiplying the length by the square of the diameter (V=Ld2). Significance for all statistical tests was set at p:s;0.05. During dissection, the crop and ventriculus of each wasp as also dissected and examined for content. The head widths (an indicator of size in wasps) of the 20 E. foraminatus were m asured using a dissecting microscope a d ocular micrometer. RESULTS The average total egg volume (the 2 largest eggs) for the group given prey (0.809 mm3) was significantly greater than for the group denied prey (0.330 mm3) (t=3.75,p<0.001). The average largest egg volume for the experimental group (0.520 mm3) was significantly greater than for the control (0.255mm3) (t=3.32, p<0.005). The average smallest egg volume for the experimental 2The Great Lakes Entomologist, Vol. 25, No. 4 [1992], Art. 8https://scholar.valpo.edu/tgle/vol25/iss4/81992 THE GREAT LAKES ENTOMOLOGIST 299 group (0.289 mm3) was significantly greater than for the control (0.075mm3) (t=3.45, p <0.005). The average h ad width of the group fed on prey (3.28mm) and the group denied prey (3.25mm) were not significantly different (t=0.268, p >0.1). This was important, because Larrson (1990) and O'Neill (1985) found strong correlations between head size and egg size in sphecid wasps. All wasps fed on the sugar solutions provided, but none showed any interest in the cups containing pollen. The crops of dis ected wasps were found to bedistended with sugar solution. When we dissected wasp ventriculi, we found no fragments of prey, although the ventriculi did tak  on the darker color of p ey tissues after wasp feeding. We estimate that individual wasps ate from 6 to 18 caterpillars after being given access to prey. Due to difficulties of observation, it seems likely that the high end of the range is closest to the actual number of prey eaten. There was a distinct period before nesting began, when the wasps each ate approxi­mately 4 caterpillars. After nesting and provisioning began, however, all females were observed eating prey at vari us tim s which we could not corre­late with any phase of the nesting cycle. When wasps were deprived of prey (twice, each time for one week) nest cavities were partitioned and closed with mud, but no eggs were found. Because eumenids oviposit before provisioning, cells with only eggs might be expected if the presence of prey were not needed to stimulate ovarian development (through feeding). Prey captured and fed upon by adult females were not always stung first. Individuals of E. foraminatus were more likely to chew through the prey's cervical area to kill it, and then devoure the rest of the prey without a strug­gle. Feeding always began on the last abdominal segment and lasted from 2 to 15 min. Larger caterpillars were often only partly eaten and discarded, while smaller prey were devoured leaving only the head capsule. While eating prey, a wasp holds the caterpillar by the abdomen with her forelegs and curls h r abdomen under the prey in a position similar to stinging.This position made t difficult to discern whether wasps were just holding p y or stinging it. Smaller prey were less likely to be stung because of difficulties involved in locating the normal sting region and the ease of subduing a small victim by biting it. DISCUSSION Our observations of prey-feeding by adult eumenids contradict the view that adult wasps feed to acquire fluids on ry days (Lin 1978). Our wasps were always provided with an ample supply of water, yet still fed on prey. The idea that adult feeding behavior is a response to flower nectar scarcity (Evans and West-Eberhard 1970) is contradicted by our observations of distended crops (filled with sugar solution) found in females iss cted during the period we observed prey-feeding. This indicates that the absence of nectar is not what stimulates prey-feeding. Nor was there any indication that eating prey was a displacement activity exhibited by wasps in response to novel r confusing situations. Rather, it is a normal necessary activity associated with egg devel­opment. Our results are in line with numerous studies of parasitoid Hymenop­tera that require maturation feeding on hosts (prey) for full egg development (DeWilde 1964). Flanders (1942) explained that in many species of Hymenop­tera larval nutrition is insufficient for egg development to proceed in the adult without further feeding, adding that these adult females habitually feed on the body fluids of their hosts prior to oviposition. Our measurements of eggs for wasps which did not feed on prey (some eggs almost as large as those of prey-fed wasps) indicate that vitellogenesis begins in eumenid females in the 3Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: EPublished by ValpoScholar, 1992300 THE GREAT LAKES ENTOMOLOGIST Vol. 25, No.4 absence of prey or protein sources other than those acquired as larvae. Prey­feeding is essential to maturation of more than one egg (wasps not fed prey as adults had only one developing egg) and possibly even for maturation of the first egg. This condition is similar to that described by Flanders (1935) for the Pteromalidae and found in several dipteran species (Clements 1963). Until now research on the effects of prey-feeding on ovarian development had not been carried out for solitary predatory wasps. The many reports of prey-feeding (on the body fluids) by adult female Sphecidae (Evans 1966a), eumenids (Iwata 1953), and pompilids (Rau 1945) have not been correlated with ovarian development. It is likely that these many anecdotal reports of predatory solitary wasps feeding on prey are involved with egg maturation. It also seems likely that more intensive studies of predatory behavior will reveal prey feeding to be a regular part of female activities and not something brought on by adverse conditions (i.e lack of water). Total mastication of prey as we observed for eumenids has been observed for social species. Rau (1945) described workers of Polistes spp. thoroughly pulping caterpillar prey in their jaws so that it could be swallowed. Chapman (1963) found Vespula pennsylvanica (Saussure) feeding on swarming reproduc­tive ants. Wasps were observed "dozens of times" capturing ants and landing to chew their prey, while no prey was seen to be carried back to the nest. Examinations of the ventriculi of 20 wasps failed to reveal any ant fragments, implying that only body fluids were ingested. Unlike the soft, thinly sclerotized lepidopterans fed on by eu~enids, the heavily sclerotized nt cuti­cle would be difficult to digest. This, along with the need for adult wasps (with a narrowed esophagus) to finely chew their food, probably is related to why no fragments were found. Chapman (1963) described the wasps biting off the heads of their ant prey and "prefering" to feed on the abdomen rather than the thorax, behaviors we described earlier for E. foraminatus. This behavior has also been described by Ross (1983) for Vespula spp. which assume the same posture we described for solitary vespids feeding on prey, enclosing "the strug­gling prey with the ventral surface of the gaster, the legs, and the mouthparts". Gillaspy (1979) gave descriptions of Polistes spp. returning to the nest with no apparent load with dissected crops containing a "thin gruel of protein food with recognizable insect parts". Among vespids, the transition from solitary to social life has also involved the transition from feeding larvae intact prey items to feeding young com­pletely masticated prey meat. Our results indicate that the complete chewing of prey was likely well e tablished among the solitary ancestors (as a preadap­tation) of the living social species. LITERATURE CITED Askew, R. R. 1971. Parasitic insects. American Elsevier Publishing Company, Inc., NY. pp. 136-137,152. Burdick, D. J., and M. S. Wasbauer. 1959. Biology of Methoca califomica Westwood. Wasmann J. BioI. 17:75-88. Chapman, J. A. 1963. Predation by Vespula wasps on hilltop swarms of winged ants. Ecology 44:766-767. Clements, A. N. 1963. The physiology of mosquitoes. The MacMillan Company, NY. pp. 169-175. DeWilde, J. 1964. Reproduction. In: M. Rockstein (ed.). The physiology of Insecta. Vol. 1. Academic Press, NY. pp. 10-58. Evans. 	H. E. 1966a. The comparative ethology and evolution of the sand wasps. Harvard University Press, Cambridge, Mass. pp. 427-429. 4The Great Lakes Entomologist, Vol. 25, No. 4 [1992], Art. 8https://scholar.valpo.edu/tgle/vol25/iss4/81992 THE GREAT LAKES ENTOMOLOGIST 301 __. 1966b. The behavior patterns of solitary wasps. Ann. Rev. Entomol. 11:123-154. Evans, H. E., and M. J  West· Eberhard. 1970. The wasps. Univeristy of Michigan Press, Ann Arbor. p. 59. Evans, H. E., and C. M. Yoshimoto. 1962. The ecology and nesting behavior of the Pompilidae of the northeastern United States. Misc. Pub!. Entomol. Soc. Am. 3:65-119. Finlayson, L. H. 1950. The biology of Cephalonomia waterstoni Gahan, a parasite of Laemophloeus. Bull. Entomol. Res. 41:79-97. Flanders, S. E. 1935. An apparent correlation between the feeding habits of certain pteromalids and the condition of their ovarian follicles. Ann. Entomol. Soc. Am. 28:438-444. 1942. Oosorption and ovulation in relation to oviposition in the parasitic Hyrne· noptera. Ann. Entomol. Soc. Am. 35:251-266. Gillaspy, J. E. 1979. Management of Polistes wasps for caterpillar predation. South· western Entomol. 4:334-352. Huber, A. 1961. Zur biologie von Mellinus aruensis L. Zool. Jahrb. (Syst.) 89:43-118. Hunt, J. H. 1991. Nourishment and the evolution of the social Vespidae. In: K.G. Ross, and R.W. Matthews (eds.). The social biology of wasps. Comstock Publishing Associ· ates, Ithaca, NY. pp. 426-450. Hunt, J. H., I. Baker, and H. G. Baker. 1982. Similarity of amino acids in nectar and larval saliva: the nutritional basis for trophallaxis in social wasps. Evolution 36:1318-1322. Hunt. J. H., P. A. Brown, K. M. Sago, and J. K. Kerker. 1991. Vespid wasps at pollen (Hymenoptera: Vespidae). J. Kans. Entomo!. Soc. 64:127-130. Irnms, A. D. 1957. A general textbook of entomology. Methuen, London. p. 525. Iwata, K. 1953. Biology of Eumenes in Japan. Mushi 25:25-47. __. 1976. Evolution of instinct: comparative ethology of Hymenoptera. Amerind, New Delhi. 535 pp. Larrson, F. K. 1990. Female body size relationships with fecundity and egg size in two solitary species of fossorial Hymenoptera (Colletidae and Sphecidae). Entomol. Gener. 15:167-171. Leclercq, J. 1959. Une population de Mellinus arvensis L. d ns laquelle les fernelles chassent pour leur propre compte (Hym. Specidae Nyssoninae). Bull. Soc. Royale Sciences Liege 28:246-249. Lin, N. 1978. Sequential hypermalaxation in the digger wasp Diodontus franclemonti Krombein (Hymenoptera: Sphecidae). J Kans. EntomoL Soc. 51:235-238. Malyshev, S. I. 1968. Genesis of the Hymenoptera and the phases of their evolution. Methuen, London. pp. 182-185. O'Neill, K.M. 1985. Egg size, prey size. and sexual size dimorphism in digger wasps (Hymenoptera: Sphecidae). Can. J. Zool. 63: 2187-2193. Rau, P. 1945. The carnivorous habits of the adult wasp Odynerus dorsalis Fab. Bull. Brooklyn Entomol. Soc. 40:29-30. Ross, K. G. 1983. Studies of the oraging and feeding behavior of yellowjacket foun· dresses, Vespula (Paravespula) (Hymenoptera: Vespidae), in the laboratory. Ann. Entomol. Soc. Am. 76:903-912. Spradbery, J. P. 1973. Wasps: an account of the biology and natural history of solitary and social wasps. University of Washington Press, Seattle. pp. 43-44. 5Chilcutt and Cowan: Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: EPublished by ValpoScholar, 1992

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Carnivory in Adult Female Eumenid Wasps (Hymenoptera: Vespidae: Eumeninae) and Its Effect on Egg Production

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