Parasitoids of herbivorous, sessile and non active hosts face the problem of using detectable and reliable cues during host location more than parasitoids of mobile and active hosts. In the case of the egg parasitoids of pentatomid bugs (Heteroptera: Pentatomidae), parasitoid searching during the early phases of host location is known to be mediated by volatile cues. Instead, very little has been done on the cues used during the final steps, when the parasitoid is walking on the plant substrate in the vicinity of the host eggs. This phase may be usefully investigated considering the host unit, previously defined as the ensemble of physical and chemical characters of the host, the substrate and the associated material. Here we report laboratory observations on the influences of cues from the Nezara viridula (L.) host unit on Trissolcus basalis Wollaston (Hymenoptera: Scelionidae). These are visual cues from the eggs, as such or associated with volatiles, the latter either from the host eggs or induced by host egg - plant interactions. Bioassays of host egg clusters or glass models of the clusters were conducted in open arenas with the aid of an automated image system. T. basalis females show an orientation response to the complex of cues from the host egg clusters and to the combination of visual cues and host egg volatiles from treated glass models. Results are discussed in relation to those obtained from bioassays conducted in Y-tube olfactometer, showing a response by T. basalis females to volatiles induced by host egg - plant (Vicia faba) interaction.
Species 1: Heteroptera Pentatomidae Nezara viridula (southern green stink bug)
Species 2: Hymenoptera Scelionidae Trissolcus basalis
Keywords: Egg parasitoid
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