Effects of oviposition in a non-host species on foraging behaviour of the parasitoid Cotesia glomerata

Parasitoids lay their eggs in or on a host, usually another insect. During
foraging, parasitoids can encounter insects that differ in terms of host
suitability and quality. At one extreme end of this spectrum are non-hosts
that are unsuitable for offspring development. Non-hosts are generally
ignored but parasitization does occur and occasionally also results in egg
deposition. Here, we investigate how oviposition in a non-host influences
subsequent foraging behaviour of a parasitoid and whether this is mediated
by learning. Our study system consists of the endoparasitoid Cotesia
glomerata and the presumed non-host caterpillar Mamestra brassicae. In the
presence of Pieris brassicae hosts and/or their traces (frass), we
observed that C. glomerata inserts its ovipositor into M. brassicae
caterpillars. Eggs were deposited, but all eggs disappeared within 96h,
confirming the non-host status of M. brassicae. In contrast to our
expectation, there was no memory retention after oviposition in a non-host
and parasitoids did not alter their behaviour with respect to non-host
contacts and ovipositions. Instead, C. glomerata became more motivated to
forage on a non-host infested leaf. We propose that egg deposition in
non-hosts by C. glomerata might be due to their high egg load, which is
thought to make parasitoids less selective on host quality, especially
when they have few reproductive opportunities. In such cases, fitness
costs to individual females are low. Egg deposition in non-hosts might
ultimately lead to host range expansion if parasitoids overcome the
defence response of non-hosts over evolutionary time.