Adult nourishment during larval provisioning in a primitively Eusocial

Insectes Sociaux, Paris
9
M a s s o n , P a r i s , 1984
1984, V o l u m e 31, n ~ 4, p p . 452-460
ADULT NOURISHMENT DURING LARVAL PROVISIONING
IN A PRIMITIVELY EUSOCIAL WASP,
POLISTES METRICUS SAY
ff.H. HUNT
Department of Biology, University of Missouri-St. Louis,
St. Louis, Missouri 63121 U.S.A.
Re~u le 29 n o v e m b r e 1983
Accept6 le 17 aofit 1984
SUMMARY
I n the laboratory, female Polistes metricus on recently collected nests malaxated
larval provisions containing radioactive fructose. Recovery of radioactivity f r o m the
adults s h o w e d t h a t they extracted substantial liquid or semisolid material f r o m the
provision m o r s e l during malaxation. The extracted material was held in the crop, and
it could be regurgitated. Adults allowed to regurgitate to larvae exhibited significantly
less radioactivity t h a n w a s p s isolated before regurgitation could occur.
Midguts
and wing muscles f r o m provisioning adults s h o w a p a t t e r n of radioactivity assimilation,
with peaked activity at two hours following malaxation. These results c o n f i r m a
previously o b s e r v e d p a t t e r n of larval provisioning and, for the first time, d e m o n s t r a t e
adult n o u r i s h m e n t to be concomitant with the provisioning behavior.
RESUME
Alimentation de I'adulte au cours de I'approvisionnement des |arves
chez une gu6pe primitivement eusociale, Polistes metricus Say
Au laboratoire, la femelle de Polistes metriczts sur des nids r ~ c e m m e n t r~colt~s
m a l a x e n t des provisions destindes aux larves, contenant du fructose radio-actif. Le fair
que de la radio-activitd se retrouve chez les adultes m o n t r e qu'ils extraient une p a r t
substantielle de liquide ou de matdriel semi-solide au cours de la malaxation de ces
provisions. Ce matdriel extrait se retrouve au niveau du gdsier et peut 6tre r6gurgitd.
Les adultes ayant la possibilitd de rdgurgiter atLx larves m a n i f e s t e n t une radio-activitd
significativement infdrieure aux gu6pes raises en isolement avant de pouvoir rdgurgiter.
L'intestin m o y e n et les muscles alaires des approvisionneuses m o n t r e n t un p a t r o n d'assimilation radio-active, avec un pic d'activitd deux heures aprbs la malaxation. Ces
rdsultats c o n f i r m e n t un p a t r o n d ' a p p r o v i s i o n n e m e n t des larves p r d c d d e m m e n t observ6
et, p o u r la p r e m i b r e lois, d 6 m o n t r e n t une alimentation de l'adulte en relation avec le
comportement d'approvisionnement.
ADULT NOURISHMENT
IN POLISTES METRICUS
453
INTRODUCTION
S o c i a l w a s p s of t h e f a m i l y V e s p i d a e a r e well k n o w n to m a l a x a t e p r e y
b e f o r e p r o v i s i o n i n g t h e i r larvae. T h a t is, a f e m a l e w a s p t a k e s an i n s e c t o r
i n s e c t f r a g m e n t a n d chews o r squeezes it w i t h h e r m a n d i b l e s , u s u a l l y while
r o t a t i n g it w i t h h e r forelegs, b e f o r e feeding the r e s u l t a n t p u l p y m a s s d i r e c d y
to larwe. M a l a x a t i o n of p r e y (not l a r v a l p r o v i s i o n s ) o c c u r s i n f r e q u e n t l y b u t
in a p p a r e n t l y a w i d e v a r i e t y of social a n d non-social w a s p s (EVANS a n d
EBERHARD, 1970). F o r e x a m p l e , LIN (1978) r e p o r t s , h y p e r m M a x a t i o n ,, (HuBER,
1961, in LIN, 1978) in the .digger w a s p Diodontus f r a n c t e m o n t i (Sphecid~e).
D u r i n g p e r i o d s of v e r y h o t w e a t h e r the a d u l t D. f r a n c l e m o n t i m a l a x a t e d a n d
t h e n d i s c a r d e d a series of a p h i d s , p r o b a b l y as a s o u r c e of w a t e r a n d p e r h a p s
of n o u r i s h m e n t . EVANS a n d EBERHARD (1970) n o t e that, in general, f e e d i n g
on p r e y b y a d u l t w a s p s p r o b a b l y o c c u r s u n d e r c o n d i t i o n s of s c a r c i t y of
n e c t a r o r h o n e y d e w ; t h e y also note, though, t h a t s o m e s p e c i e s m a y r e q u i r e
p r o t e i n a ~ e o u s f o o d as a d u l t s .
S p e c i e s t h a t w o u l d a p p e a r to r e q u i r e p r o t e i n a c e o u s n o u r i s h m e n t as
a d u l t s a r e t h o s e t h a t a r e long-lived and, in p a r t i c u l a r , t h a t h a v e a p r o l o n g e d
p e r i o d of r e p r o d u c t i v e activity. Queens of eusocial Vespidze a r e c o n s p i c u o u s
in t h e s e r e g a r d s . T h o u g h it has b e e n s u g g e s t e d t h a t a d u l t w a s p s m a y n o u r i s h
t h e m s e l v e s as t h e y m a l a x a t e prey, little a t t e n t i o n has b e e n p a i d to t h e
p o s s i b i l i t y t h a t a d u l t s m a y n o u r i s h t h e m s e l v e s b y m a l a x a t i o n of l a r v a l
p r o v i s i o n s . JEANNE (1972) suggested t h a t m a l e M i s c h o c y t t a r u s d r e w s e n i
(Vespid~e) t h a t m a l a x a t e d larval p r o v i s i o n s a r e ~, m o r e selfish t h a n w o r k e r like x- in t h a t t h e i r m a l a x a t i o n seems p r i m a r i l y d i r e c t e d t o w a r d self n o u r i s h m e n t . HrJNT a n d NOONAN (1979) p r e s e n t e d d a t a on malmxation of l a r v a l provisions b y m a l e s of t h r e e Polistes species t h a t i n d i c a t e d s u p p o r t f o r JEANNE'S
s u g g e s t i o n ; they" also n o t e d the at~sence of d a t a t o d o c u m e n t n o u r i s h m e n t
of a d u l t f e m a l e s d u r i n g ma'laxation of l a r v a l p r o v i s i o n s . The f o l l o w i n g s t u d y
w a s t h e r e f o r e d e s i g n e d to investigate the p o t e n t i a l f o r s e l f - n o u r i s h m e n t
d u r i n g m a l a x a t i o n of l a r v a l p r o v i s i o n s b y f e m a l e Polistes w a s p s :
METHODS
Colonies of Polistes metricus Say (Vespidae) were collected near St. Louis,
Missouri. Collections were made near sunset or sunrise to make it more likely that
most adults of the colony were on the nest. The nest was then attached to the ceiling
of an aluminum screen mosquito rearing cage (30 cm on a side), and the adults were
introduced into the cage. M o s t colonies were collected in the evening and used in
experiments the following morning.
Live lepidopteran larvae (Cabbage Butterfly, Pieris rapae, and Cabbage Looper,
Trichoplusia nO were collected in a local garden. In the laboratory a small (< 1 cm)
whole lepidopteran larva or a fragment of a larger larva was then used as a provision
morsel The morsel was injected, using a microliter syringle with 1 ~1 5 % ethanol
J.H.
454
HUNT
containing 1 ~Ci 14C fructose (obtained f r o m ICN Corp.). The injected morsel was
t a k e n f r o m t h e tip of the syringe onto the point of a teasing needle and offered to a
w a s p t h a t was o n t h e face of its nest. Slow, careful p r e s e n t a t i o n m a d e it possible to
m o v e the m o r s e l to t h e w a s p w i t h o u t alarming her. If the morsel could be b r o u g h t
into contact w i t h t h e w a s p ' s m o u t h p a r t s , she usually took the morsel and began to
malaxate it. The w a s p s typically malaxated the morsel for one to a few minutes
b e f o r e feeding it to larvae.
Typical provisioning behavior in these wasps involved a specific sequence of
provisioning and grooming behaviors (fig. 1) :
Accept provision
Malaxate ~ . - - .
Provision larvae with solids
Groom
A
- ~ . - - -
~ 9 t,~
~ 1 7 6 1 7 6. . . . . .
~176
~176 ....
.
....
.~
......
~
.....
Provision larvae with liquid regurgitate
. ..
o~176
B0C
~.~-Groom
The letters A and B indicate points in this sequence w h e r e w a s p s were removed
f r o m the n e s t a n d isolated as f o l l o w s : A = Group I (run in 1978), B = Group II (run
i n 1979). I n a t h i r d group of w a s p s (Group III), assayed in 1982, the provision morsel
w a s taken f r o m the adult wasp at the completion of malaxation but before any larvae
h a d received solid provision. These w a s p s were then closely observed until one o r m o r e
larvae h a d been visited (for possible provisioning with liquid regurgitate) and the adult
t h e n g r o o m e d h e r s e l f ; during this grooming, then, she was removed from the nest and
isolated. The d o t t e d a r r o w a n d letter C in the flow diagram illustrate this sequence.
The isolated w a s p s were held in 500 ml plastic containers for varied time periods
(see Results). Following that, the Group. I and Group II wasps were chilled briefly in
a refrigerator and t h e n t r a n s f e r r e d to a test tube i m m e r s e d in an a c e t o n e / d r y ice bath
that froze the wasp completely in less than 30 sec. The frozen wasp was quickly divided,
u s i n g a razor blade, into four p a r t s :
1) head,
2) thorax (including p r o p o d e u m w i t h appendages,
3) a n t e r i o r gaster (abdominal segments II-IV),
4) p o s t e r i o r gaster (abdominal segments V-X).
Each of these f o u r p a r t s was placed into separate test tubes containing 1 ml 5 %
e t h a n o l and c r u s h e d using a glass stirring rod. The test tubes were then centrifuged
for 5 minutes at 10,000 g, and the s u p e r n a t a n t was decanted into a scintillation vial for
counting. The Group III w a s p s were asphyxiated using ethyl acetate.
The legs and
wings w e r e t h e n clipped o f f ; t h e w a s p was pinned to a wax pan, and the midgut and
wing muscles w e r e removed. The midgut was tied off f r o m the intact crop before
removal, and the esophagus was exposed before removing the wing muscle. The excised
tissues were t r a n s f e r r e d to separate test tubes, m a c e r a t e d in 1.0 ml NCS tissue solubilizer
(obtained f r o m A m e r s h a m / S e a r l e ) , and counted, as were the the Group I and II
samples, using 5 ml Bray's solution and a Packard Tri-Carb liquid scintillation spectrometer. Recorded counts p e r m i n u t e (CPM) w e r e converted for reporting as disinte-
ADULT N O U R I S H M E N T I N P O L I S T E S
METRICUS
455
grations p e r m i n u t e (DPM) using a n experimentally established q u e n c h i n g f a c t o r of
60%.
Once t h e e x p e r i m e n t a l w a s p s h a d been isolated, all o t h e r adult wasps on each
n e s t were p r o m p t l y collected a n d discarded. Larvae were r e m o v e d individually f r o m
t h e nest, weighed, a n d placed into test tubes containing 1 m l 5 % ethanol. The
larvae were m a c e r a t e d w i t h stirring rods, centrifuged for 5 min. at 10,1300 g, a n d the
s u p e r n a t a n t was d e c a n t e d f o r scintillation counting. A p p r o p r i a t e controls for backg r o u n d c o u n t s were r u n for all sample procedures.
RESULTS
Figure 2 p r e s e n t s t h e d i s t r i b u t i o n a m o n g t h e f o u r s a m p l e d b o d y r e g i o n s
of radioactivity
for the Group I wasps, which were isolated immediately
I
100"
cq
Z, r
10,
I
0
x
2 Hours
13..
rl
2.5 Hours_
100
10
Fig. 2. - - D i s t r i b u t i o n of recovered label activity, as disintegrations p e r m i n u t e (DPM),
f r o m G r o u p I wasps. Each h i s t o g r a m c o r r e s p o n d s to a single adult female wasps
as identified in table 1. The four b a r s of each h i s t o g r a m c o r r e s p o n d to the
four body regions n u m b e r e d in the text and in this figure o n h i s t o g r a m A. The
times t h a t the adult wasps were held in isolation are s h o w n for each of four
subgroups.
Fig. 2. - - R 6 p a r t i t i o n de la radio-activitd r~cup6rde, en d6sintdgration p a r m i n u t e (DPM),
p o u r les gu6pes d u groupe I. Chaque h i s t o g r a m m e correspond h une seule femelle
adulte c o m m e il est m o n t r 6 dans le t a b l e a u I. Les q u a t r e b a r r e s de chaque histog r a m m e c o r r e s p o n d e n t aux quatre rdgions du corps d6crites dans le texte et dans
cette figure s u r l ' h i s t o g r a m m e A. Les dur6es p e n d a n t lesquelles les gu6pes adultes
sont isoldes sont m o n t r d e s p o u r c h a c u n des q u a t r e sous~groupes.
J.H. H U N T
456
f o l l o w i n g l a r v a l p r o v i s i o n i n g . A c t i v i t y w a s f o u n d in all b o d y s e c t i o n s o f
all wasps. Distribution of the label among the four sampled body regions
i n c l u d e s s e v e r a l n o t a b l e f e a t u r e s . E l e v e n o f 16 w a s p s (A-F, K-M, O, a n d P)
s h o w h i g h e s t a c t i v i t y in t h e a n t e r i o r g a s t e r r e g i o n , w h i c h c o n t a i n s t h e c r o p .
T h r e e w a s p s (B, I , a n d O) v i s i b l y r e g u r g i t a t e d d u r i n g f r e e z i n g , a n d t h e s e
w a s p s s h o w s u b s t a n t i a l a c t i v i t y in t h e h e a d r e g i o n . T w o o f t h e t i m e p e r i o d
s u b - g r o u p s (1 h r a n d 2.5 h r ) s h o w s i g n i f i c a n t l y n o n - r a n d o m p a t t e r n i n g o f
a c t i v i t y a m o n g t h e f o u r b o d y r e g i o n s (FRIEDMAN t w o - w a y a n a l y s i s o f v a r i a n c e ,
X2 = 7.1 a n d 8.8 ; b o t h p < .0001 (SIEGEL, 1956). T h e p a t t e r n o f l a b e l disr
t r i b u t i o n is r a n d o m a t 1.5 h r (• = 3.3 ; .4 < p < .5) a n d a t 2 h r (• =
1.1 ; .8 < p < .9).
r
r
R e c o v e r e d D P M f r o m G r o u p I I w a s p s (fig. 3), w h i c h w e r e i s o l a t e d f o r 1 h r
f o l l o w i n g c e l l v i s i t s ( m e a n t i m e b e t w e e n f i r s t a n d s e c o n d g r o o m i n g s = 5.7
r a i n . ; r a n g e = 1.5 to 11.5 rain), w a s d i s t r i b u t e d n o n r a n d o m l y a m o n g t h e
:four b o d y r e g i o n s (• = 151.7 ; p < .0001) ; six o f 8 w a s p s h a v e h i g h e s t
r
r e c o v e r e d a c t i v i t y in o n e o f t h e g a s t e r r e g i o n s .
G r o u p I a n d G r o u p I I w a s p s d i f f e r s i g n i f i c a n t l y in % D P M r e c o v e r e d
f r o m t h e a d u l t s (table I ; M a n n - W h i t n e y U = 10.5, p < .002 [SIEcEL, 1956]),
with lower recovery from Group II wasps, which had been permitted to
regurgitate crop contents to larwe.
Table I s u m m a r i z e s t h e % D P M r e c o v e r e d d a t a f r o m G r o u p s I a n d I I .
N o s i g n i f i c a n t d i f f e r e n c e e x i s t s b e t w e e n g r o u p s in % D P M r e c o v e r e d f r o m
3
e~
I-I
!
o
v--
I Hour
100
10
AL
-Fig. 3. - - Distribution of recovered label activity, as disintegrations per minute (DPM),
from Group II wasps. Each histogram corresponds to a single adult female wasp
as identified in table 1. The four bars of each histogram correspond to the four
body regions numbered in the text and in this figure on histogram Q. All
Group II wasps were held in isolation for one hour.
-Fig. 3. - - Distribution de la radio-activit6 r6cupdr6e, en d6sintdgrations par minute
(DPM), pour les gu6pes du groupe II. Chaque histogramme correspond ~t une
seule femelle adulte, comme il est montr6 dans le tableau I. Les quatre barres
de chaque histogramme correspondent aux quatre regions du corps d6crites
dans le texte et dans cette figure sur l'histogramme Q. Toutes les gu6pes du
groupe II ont 4t6 maintenues en isolement pendant une heure.
ADULT NOURISHMENT
IN POLISTES
METRICUS
457
Table I. m Recovery of r a d i o a c t i v e label activity f r o m adults and larvae of Polistes
metricus on experimental nests,. Data are presented as % of label injected into
the provision morsel and m e a s u r e d as disintegrations per m i n u t e (DPM). The
provision m o r s e l was either a small, whole lepidopteran larva (w) o r f r a g m e n t
of a larger lepidopteran larva (f). The experimental adults are identified by
letters (A, B, ..., W') t h a t c o r r e s p o n d to the letters s h o w n in Figures 1 and 2.
When m o r e t h a n one wasp was p r e s e n t on a nest no a t t e m p t was m a d e to discriminate queens f r o m workers. Group I w a s p s were assayed on the dates shown
in 1978; Group II dates are for 1979.
Niveau de radio-activit6 retrouv6 chez les adultes et les larves de Polistes
metricus sur des nids exp6rimentaux. Les donn6es sont pr6sent6es en pourcentage
Tableau I. u
du niveau inject6 dans le morceau de n o u r r i t u r e et mesur6es en d6sint~grations
p a r m i n u t e (DPM). Le m o r c e a u de nourriture 6tait soit une petite larve de 16pidopt~re enti6re OR), soit un f r a g m e n t de larve plus grande (f). Les adultes exp6r i m e n t a u x sont identifi6s p a r des lettres (A, B, ... W') qui c o r r e s p o n d e n t h celles
qui figurent dans les figures 1 et 2. Quand plus d'une gu~pe 6tait pr6sente sur
un nid, nous n'avons pas recherch6 h discriminer les reines .des ouvri~res. Les
gu~pes du groupe I ont 6t6 exp6riment~es aux dates montr6es en 1978; les dates
du groupe II c o r r e s p o n d e n t ~ 1979.
Nest
Date
Experimental
Adultes
Total ~
Adults
on Nest
Provision
Morsel
% DPM Recovered
.Adults
Larvae
Nest
Total *
21 Jul
25 Jul
26 Jul
26 Jul
28 Jul
28 Jul
28 Jul
1 Aug
1 Aug
4 Aug
4 Aug
4 Aug
A,B
E
H
I
C
J.L
F,G
D
K
M,N
O
P
4
3
2
6
2
3
5
4
3
3
4
5
f,f
w
w
w
f
w,w
f,f
w
f
?,?+
?
?
5.9, 33.4
45.3
17.9
23.4
14.0
19.8, 27.9
40.0, 14.1
77.4
49.8
16.5, 10.4
40.5
8.0
5.5
14.5
4.5
21.8
20.8
10.4
8.0
9.5
15.9
41.3
37.,8
45.3
25.2
59.8
22.5
45.3
34~8
34.3
35,1
86.9
65.8
54.7
78.3
53.4
27 Jun
27 Jun
27 Jun
3 Jul
10 Jul
11 Jul
11 Jul
Q
R
S
T
U
V
W,W'
1
1
1
1
5
5
5
f
f
w
?
f
f
f
23.4
12.4
0.9
6.0
0.2
0.3
0.4, 3.9
7.8
13'5
19.9
54.2
37.9
28.1
33.7
31.2
25.9
20.7
60.2
38.1
28,4
36.0
Group I
1
2
3
4
5
6
7
8
9
10
11
12
Group II
13
14
15
16
17
18
19
* Total DPM recovery is less t h a n 100 % due to experimental procedure. Background
counts w e r e high, especially for large larvae, and excretion by isolated adults was
uncontrolled for, Also, equal initial counts in all provision morsels w e r e assumed
but not d e m o n s t r a t e d .
+ ~ Signifies u n r e c o r d e d data.
.I.H. H U N T
458
larvae ( M a n n - W h i t n e y U = 22 ; n.s.) ; n o s i g n i f i c a n t d i f f e r e n c e i n % D P M
r e c o v e r e d is a t t r i b u t a b l e t o t h e ~provision m o r s e l " b e i n g e i t h e r a w h o l e
l a r v a o r a f r a g m e n t ( M a n n - W h i t n e y U = 20 ; n.s.). N o s i g n i f i c a n t b e t w e e n g r o u p d i f f e r e n c e e x i s t s i n t o t a l % D P M r e c o v e r e d f r o m a d u l t s a n d larvae
c o m b i n e d ( M a n n - W h i t n e y U = 18 ; n.s.). A m o n g t h e G r o u p I I w a s p s , w h i c h
w e r e i s o l a t e d f o l l o w i n g v i s i t s t o l a r v a : in w h i c h r e g u r g i t a t i o n m i g h t h a v e
o c c u r e d , six a d u l t s ( S - W ' ) r e t a i n e d v e r y l i t t l e l a b e l a c t i v i t y , b u t t w o (Q, R )
retained substantial amounts of label activity. The wet weight distributions
o f a l / larvae d i d n o t d i f f e r b e t w e e n G r o u p s I a n d I I ()2 = 4.57 ; n.s.).
r
Thot~gh t h e G r o u p I I w a s p s w e r e p e r m i t t e d a n o p p o r t u n i t y t o r e g u r g i t a t e c r o p c o n t e n t s t o tarva~, lai-vae r e c e i v i n g r e g f i r g i t a t e c o u l d n o t b e
d i s t i n g u i s h e d f r o m larvae r e c e i v i n g p r o v i s i o n m o r s e l . I n G r o u p I I , t h e r e f o r e ,
the morsel was taken from the adult female before provisioning ; she was
t h e n o b s e r v e d u n t i l s h e v i s i t e d o n e o r m o r e .larvae a n d t h e n g r o o m e d h e r s e l f ; t i m e d i s o l a t i o n w a s t h e n b e g u n . I n 3 o f 12 n e s t s n o r a d i o a c t i v i t y
w a s r e c o v e r e d f r o m a n y larvae ; in 4 n e s t s , 1 l a r v a s h o w e d l a b e l a c t i v i t y ;
i n 5 n e s t s , 2 larvae s h o w e d l a b e l a c t i v i t y .
T h e r a n d o m d i s t r i b u t i o n a m o n g b o d y r e g i o n s o f l a b e l a c t i v i t y in G r o u p I
a d u l t w a s p s a t 1.5 h r a n d 2 h r s u g g e s t s a s s i m i l a t i o n , b u t t h e d a t a a r e n o t
conclusive. Therefore, midgut and wing muscle tissues were excised from
G r o u p I I I w a s p s a t v a r i e d t i m e s fol,lowing i s o l a t i o n . T h e p a t t e r n o f l a b e l
a c t i v i t y is s h o w n f o r t h e a s s a y e d t i s s u e s o f G r o u p I I I w a s p s i n figure 4.
9
Midgut
OMuscle
X
121
~
2
i.
Fig. 4. - - Recovery of label activity, as disintegrations per minute (DPM), from isolated
midguts and thorasic muscle of Group III wasps, which were run in 1982.
Isolation times are shown on the abscissa. Each point on the figure is an average
for three experimental wasps.
Fig. 4. - - R6eup6ration de radio-activit6, en d6sint6grations par minute (DPM), d'intestins
moyens isol6s et de muscle thoracique de gu6pes du groupe III, qui ont 6t6
6tudi6es en 1982. Les dur6es d'isolement sont montr6es en abscisses. Chaque
point sur la figure est une moyenne de trois gu6pes exp6rimentales.
ADULT N O U R I S H M E N T I N P O L I S T E S METRICUS
459
A similar p a t t e r n is seen in b o t h tissues : low activity shortly after isolation ;
p e a k e d activity at 2 hrs of isolation ; and physiological decay of label activity at 4 h r and 8 hr.
DISCUSSION
A p a t t e r n is a p p a r e n t in the data f o r the adult wasps. A female extracts
liquid a n d / o r semisolids f r o m the provision morsel during malaxation. The
extracted material is held in the crop, which is located in the anterior
p o r t i o n of the gaster. The crop contents can be regurgitated, and regurgitation for the p u r p o s e of feeding larvm n o r m a l l y follows shortly after the
provisioning of larvae with solids. This p a t t e r n was observed in PoIistes
~adwigce b y YOSmKAWA (1962). JEANNE (1972) used colored dyes to d o c u m e n t
the same p a t t e r n in Mischocyttarus drewseni. The present data thus confirm
these earlier reports. These data show, in addition, that the m a j o r i t y of
the crop contents may be regurgitated, or a substantial p o r t i o n m a y be
retained. F u r t h e r m o r e , a portion of the crop contents is rapidly assimilated
a n d distributed to other body regions of the adult wasps ; label activity
in m i d g u t and wing muscle peaks at 2 h r then diminishes in a physiological decay curve.
At the present time it is not possible to determine the q u a n t i t y of
adult n o u r i s h m e n t that might be garnered u n d e r natural conditions by
the p a t h w a y d o c u m e n t e d here. Neither is it possible at p r e s e n t to determine the relative i m p o r t a n c e to provioning adults of this m o d e of nourishm e n t versus larva-adult trophallaxis. Larva-adult trophallaxis, however, is
viewed as having evolved as a derivative behavior of malaxation of larval
p r o v i s i o n s (HUNT, BAKER and BAKER, 1982), and so adult n o u r i s h m e n t via
malaxation of larval provisions is p r e s u m e d to have a p p e a r e d first in the
evolutionary h i s t o r y of eusocial Vespidm.
I tank Paul MROCZKOWSKI, Iskara GUPTA, Bernice BACON DEMARCO,
and especially Margaret L. MCCARTHYfor technical assistance; Donald E. GROGANfor
consultation; and George 3. GAMBOA,Joan E. STRASSMAN, Martin SA~'E, and especially
Robert L. JEANNEfor review of early drafts of the manuscript. The penultimate draft
was improved by comments from J. Gervet and an anonymous reviewer. This research
was supported in part by NSF grant DEB 7904192.
ACKNOWLEDGEMENTS.J
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