Influence of host size variation on the development of a koinobiont aphid parasitoid,Lysiphlebus ambiguusHaliday (Braconidae, Hymenoptera)

Abstract

AbstractTo determine whether host body size is the currency used by the aphidiine parasitoid,Lysiphlebus ambiguus Haliday (Hymenoptera: Braconidae), in assessing host quality, the aphid,Aphis fabaeScopoli (Homoptera: Aphididae), was reared at either high or low temperature to yield hosts of the same instar with different body sizes. Cohorts ofA. fabae raised at 15°C and 30°C and exposed to individual femaleL. ambiguusin no-choice tests were successfully parasitized in all host stages from 1st instar nymphs to adults. However, younger and smaller aphids were more susceptible to parasitism than older and larger nymphs or adults, as measured by the number of mummies produced. For aphid cohorts reared at 15°C, the proportion of female progeny, progeny adult size, and development time all increased linearly with aphid size at the time of attack. In contrast, for aphid cohorts raised at 30°C, the proportion of female progeny and progeny adult size declined with aphid size, while development time remained unaffected. Through manipulation of host rearing temperature, we have shown that at cooler temperatures the koinobiont parasitoid,L. ambiguus, responds to host size in the same way as an idiobiont parasitoid, but that this response is compromised at higher temperatures. Our results suggest that differential mortality during development is likely to influence the observed secondary sex ratio in relation to aphid size for aphid cohorts raised at higher temperatures due to disruption of the activity of the host's primary endosymbiont and that such reduced nutritional quality of aphids cannot be compensated by increased development time.