Аннотация
Patterns of host selection and
host use by insects with parasitic lifestyles are predicted to be
fundamentally dynamic, responding to environmental conditions and
physiological states. A particularly robust prediction is that the number of
mature eggs that a female carries (her "egg load") should influence
behavior. As egg load decreases, females are predicted to exhibit
increasingly selective host use patterns. We tested the hypothesis that egg
load and host size influence the behavior of the parasitoid wasp
Aphytis aonidiae attacking the armored scale insect Quadraspidiotus
perniciosus. Aphytis females can use hosts either for oviposition or for
adult "host feeding," which is the consumption of host material by
adult parasitoids. Theory predicts that host feeding should be (i)
favored by low egg loads and (ii) more prevalent on lower-quality
(smaller) hosts. We conducted observations of individual females
foraging freely in the field to determine whether hosts were used for
oviposition or for host feeding. As predicted by theory, the likelihood
that a host was used for oviposition (as opposed to host feeding)
increased with both parasitoid egg load and host size. Thus, parasitoids
exhibited higher host-selectivity at lower egg loads. Since egg load
and a parasitoid's experience with hosts were not experimentally
separated, the egg load effect could in principle have been either direct
or indirect and operating through a correlation with experience.
In either case, this result constitutes the first demonstration of
a link between physiological state and oviposition behavior by a
parasitoid in the field. Parasitoid age, as measured using a wing
wear index, did not influence behavior. A laboratory study revealed
that the relationship between a host's size and the size and initial
egg load of the parasitoid developing on that host was positive,
but that it followed a pattern of diminishing returns. No effect
of host size on behavior could be detected over the range of host
sizes that were within the asymptotic region of this relationship.
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