Ecology

Biology

Hymenoptera

Parasitoid

Paper wasp

Ichneumonidae

Spider

Zoology

Host (biology)

Vespidae

Biological Journal of the Linnean Society

Wasps in the Polysphincta group of Ichneumonidae induce their web-spinning spider hosts to construct modified 'cocoon' webs that support and protect the wasps' cocoons, but the mechanisms used by wasps to manipulate their host spiders have been unclear. We evaluate the hypothesis that wasps manipulate spider ecdysteroid moulting hormones, using the taxonomic distribution of the hosts and cocoon web types of different wasp lineages in the Polysphincta group, with new data comparing cocoon webs with the moulting webs of non-parasitized host spiders. Several predictions were confirmed: wasp and spider species have not co-evolved in a strict sense, with wasp lineages jumping between host lineages; cocoon web designs induced by closely related wasps varied widely in spiders with differing natural histories; cocoon web designs were consistently adjusted to the natural history of the spider in ways promoting wasp survival; and cocoon web designs often resembled those of moulting webs of non-parasitized spiders. Several other types of data did not fit the predictions of simple versions of the ecdysteroid hypothesis, however. We conclude that the use of ecdysteroids by the wasps to manipulate host spider behaviour is probably widespread, but that some wasps might also use other mechanisms.

Evidence that Polysphincta-group wasps (Hymenoptera: Ichneumonidae) use ecdysteroids to manipulate the web-construction behaviour of their spider hosts