Choosing suitable hosts

The parasitoid wasp Hymenoepimecis bicolor (Ichneumonidae) is able to manipulate the web-building behavior of its host, the golden silk orb-weaver Trichonephila clavipes (Araneidae). The host spider constructs a modified and complex web, which serves not only as a stable platform to suspend the wasp larva's cocoon but also as a barrier against hyperparasitoids and potential predators. Before depositing an egg on the host spider's abdomen, the H bicolor female immobilizes the spider by inserting its ovipositor – and releasing paralyzing substances – into the spider's mouth. Selecting a host of the proper size is essential: too small a spider may provide an insufficient source of food for the developing larva, whereas too large a spider may pose a serious risk during host interception and immobilization.

The attacking and subduing behaviors of polysphinctine wasps are not well known but may involve sophisticated sequences, including pulling a thread of the intended host's web with the foreleg, imitating struggling prey, to attract the spider (Entomol Sci 2009; doi.org/10.1111/j.1479-8298.2009.00338.x) and waiting for an opportunity to attack while resting on the web's non-viscid barrier threads (Naturwissenschaften 2007; doi.org/10.1007/s00114-006-0177-z). The above-described direct attack behavior of H bicolor, however, is preceded by a short period in which the wasp hovers around the potential host. Would it be possible for the female wasp to correctly evaluate the risks and quality of their potential hosts with just a quick visual inspection? Are chemical cues involved in host selection?