Divergence in host utilisation by two spider ectoparasitoids within the genus Eriostethus (Ichneumonidae, Pimplinae).

Polysphinctine wasps are exclusive parasitoids of spiders and their host utilisation strategies are highly taxonomically specific. In this study, the host utilisation of two Australasian parasitoid wasps of the genus Eriostethus was studied for the first time.

Our study revealed considerable differences in host-parasitoid interactions between Eriostethus minimus associated with 3D tangle web-building spiders from the family Theridiidae (new family record for Eriostethus) and E. perkinsi associated with 2D orb-web  weaving spiders from the family Araneidae. A pupa of the former species was located in a spider retreat in the centre of an unmodified 3D tangle web and the pupal cocoon had a sparsely woven and partially transparent wall. In contrast, a cocoon of the latter species was suspended at the centre of a modified irregular sparse 3D cocoon web and the pupal cocoon had a strong, densely woven cocoon wall. This difference in host utilisation is not in agreement with the synonymisation of Millironia with Eriostethus.