Right: Males of this species, while 
copulating, fly from flower to flower 
collecting nectar. Every few minutes, 
the female in a mating pair will twist 
around and drink directly from the 
male’s mouthparts. Far right: These 
thynnine wasps spend the night in 
pairs on the plants from which they 
gather nectar. In the morning the 
males resume feeding their attached 
mates. The females’ coiled carrying 
position is typical of their species. 
lation. In a species found in southern 
Australia, the male, after achieving cop- 
ulation, excretes from the tip of his 
abdomen a large drop of viscous fluid 
that the female imbibes while coiled in a 
U position beneath his abdomen. 
All thynnine males expend consider- 
able effort, either before acquiring a 
mate or during copulation, to secure 
food for the female. Collecting nectar 
consumes time and energy that cannot 
be allocated to the search for additional 
mates and thus reduces the number of 
females a male can find in his lifetime. 
How is male reproductive success ad- 
vanced by the expenditure of effort to 
gather nuptial gifts? Because females 
are wingless, they are probably unable 
to collect food as efficiently as a male. 
By providing a nuptial gift for a female, 
a male saves her the expense of gather- 
ing nectar, enabling her to spend more 
time and energy searching for a beetle 
larva on which to lay her egg. Moreover, 
the helpful male provides his mate with 
nutrients that may contribute directly or 
indirectly to egg development. There- 
fore, if the gift-giving male’s sperm are 
used to fertilize the female’s egg, he is 
investing in the propagation of his genes 
when he feeds her. 
Indications are that females that have 
been adequately fed will not mate again 
for some time. After nuptial feeding, the 
pair flies t,o a spot likely to contain larval 
prey. As they circle low over the ground, 
the female disengages from the male 
and falls to the earth. She remains im- 
mobile for a minute or two and then 
springs to life, scuttling across the 
ground for a short distance before bur- 
rowing into the soil, often at the base of 
a weed or grass clump. Australian ento- 
mologist T.J. Ridsdill Smith found in his 
study of Hemithynnus hyalinatus that 
females remain underground for about a 
week, reemerging to call again for an- 
other male, another meal, and another 
copulation. Presumably, if the female 
had succeeded in finding a beetle larva 
during her week in the earth, the larva 
would carry an egg fertilized by the 
sperm of her most recent partner. Per- 
haps if females do not receive sufficient 
nutrients to sustain them for some time 
underground, they will resume calling at 
once when released by a male, attract 
another partner, and receive sperm from 
him that might supplant those donated 
by the inferior gift giver. (Geoffrey 
Parker of the University of Liverpool 
has found that in insects whose females 
engage in multiple matings, the last 
male to copulate before egg laying usu- 
ally has a reproductive advantage.) 
I performed many simple experi- 
ments in which I captured and sepa- 
rated mating pairs of several species 
that had not completed their period of 
nuptial feeding. Although this must 
have been a somewhat traumatic experi- 
ence for the wasps — rough handling was 
often necessary to get them to disen- 
gage — in most cases the female re- 
sumed calling almost at once, some- 
times even before she had been removed 
from the insect net in which the pair had 
been captured. It was not unusual to 
have several males buzzing frantically 
about the net a minute or two after a 
copulating pair had been separated. 
These experiments indicate that females 
do have the potential to mate more than 
once in a short period. Hence a gift- 
giving male does gain an advantage by 
feeding his mate adequately, thereby 
encouraging her to go underground to 
search for beetle larvae after mating 
with him rather than remaining above 
ground and soliciting another mating 
and more food. 
Thus females that are able to mate 
multiply and displace old sperm with 
each copulation can actually make it 
advantageous for a male to provide a 
food gift for them. When nuptial pres- 
ents originate, the trait will spread be- 
cause the sperm of males that do not 
feed mates will tend to be superseded by 
the sperm of gift-giving males. Male 
wasps provide the present because it is 
in their own genetic interests to do so, 
but in one sense they have been manipu- 
lated by the mating behavior of females. 
If egg fertilization becomes contingent 
upon receipt of an acceptable meal, only 
males that offer food will receive a ge- 
netic return from copulating. 
Given the advantages to female hang- 
ing flies and thynnine wasps in receiving 
assistance from their mates, one won- 
ders why other female insects have not 
evolved traits that make helpful actions 
the adaptive option for males. Perhaps 
they have. For a growing number of 
species, ranging from houseflies to but- 
terflies, it is now known that males 
transfer materials along with the sperm 
during copulation and that the quantity 
of these substances determines how long 
the female waits before she copulates 
again and receives a competitor’s sperm. 
In some cases it has been established 
that the extra materials are metabolized 
by the female and used to produce her 
eggs. Thus males of many insects may 
be forced to offer nuptial presents in one 
form or another if they are to fertilize 
the eggs of their mates. □ 
40 
