Host selection and cocoon web variation induced by the parasitoid wasp Acrotaphus chedelae

Parasitoid wasp adult females need to select optimally sized hosts to ensure sufficient nourishment for their larvae. Ichneumonid polysphinctine spider-ectoparasitoids have commonly been observed attacking medium-sized host spiders. This behavior may result from a trade-off between ensuring enough mass for larvae and avoiding larger, more dangerous spiders. However, exceptions to this tendency have been documented. Acrothapus chedelae, for example, seems to mainly target medium-small individuals of Argiope argentata. We hypothesized that medium-small spiders can be optimal hosts if they provide enough mass for the wasp larvae. Instead, a higher incidence of parasitoids was noted in small spiders. Despite this, the hypothesis was supported since spiders in this category had body masses significantly greater than those of adult wasps. This mass surplus is likely crucial for larval development, given the energy expenditure required until pupation and the possibility that some host spiders may not acquire enough prey during the brief period of parasitoidism. This study advances our theoretical understanding of size biases in host selection by parasitoid wasps. Most previous studies have focused solely on parasitoid-host size relationships, often overlooking the mass available in the hosts and the energy requirements for larval development. Finally, we also described the variation in cocoon webs and their construction induced by A. chedelae larva on female A. argentata spiders.