Seduction on the Wing 
Male thynnine wasps have been known 
to carry off a female, copulate with 
her in flight, then drop her 
by John Alcock 
Among insects, parental behavior is 
fairly widespread and sometimes highly 
sophisticated. But the active parent is 
almost always the mother. An explana- 
tion of why, in general, male insects 
provide their mates only with their 
sperm can be gleaned from evolutionary 
theory. Evolution occurs when individ- 
uals differ in how many of their genes 
they are able to pass on to the next 
generation. If there is variation in the 
behavior of males in a species, with 
some males offering assistance to their 
mates and others providing sperm only, 
logic dictates that the number of genes 
contributed by the two types will deter- 
mine which behavior spreads through a 
population over time and which will 
disappear. There is good reason to be- 
lieve that, under most conditions, males 
that provide their mates with nothing 
more than sperm and attempt to copu- 
late as frequently as possible will outre- 
produce those that allocate some of their 
limited time and energy to help one or 
more of their female partners. 
To understand why this is the case, 
consider that males produce smaller ga- 
metes than females: sperm are much 
smaller than eggs. A male usually is able 
to manufacture so many sperm that he 
could theoretically fertilize a large pro- 
portion of the eggs produced by all 
accessible females. The male that copu- 
lates with a large number of females will 
have great genetic influence on the next 
generation, and so the potential evolu- 
tionary pay-off of a “Casanova strategy” 
is extremely large. In contrast, a male 
that invests in mate-helping behavior 
must divert energies that could go to- 
ward finding and copulating with addi- 
tional females. The helpful male limits 
his opportunities to pass on his genes to 
the progeny of the relatively few fe- 
males he can assist. 
Yet there are male insects that do 
provide useful services or materials to 
their partners, as in the case of male 
giant waterbugs that carry the eggs of 
their mates on their backs until the 
young hatch. In other species, males 
provide food that is used to feed their 
offspring. Among the dung beetles there 
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