Foraging behaviour of a scelionid egg parasitoid exploiting chemical footprints from associated and non-associated host

Chemical footprints deposited by herbivorous pentatomid host bugs hosts when walking on the plant are adsorbed by leaf surfaces and perceived as substrate borne semiochemicals by scelionid egg parasitoids during host selection process. They act as indirect host-related cues, as they are not able to “promise” to parasitoid females the presence of the suitable host stage, but they drive them in the areas where their hosts are potentially present. Once in contact with host chemical footprints, scelionid wasps evidence an innate arrestment response characterized by an intense searching behaviour on host-contaminated areas. Exploiting of these cues allows the parasitoids to optimize their searching behaviour, since wasp females are able to discriminate the host gender and to distinguish associated from non-associated hosts. Here we investigated the response of Trissolcus basalis females, a natural enemy of several pentatomid species to chemical footprints left by Halyomorpha halys (Heteroptera: Pentatomidae) an herbivorous alien bug that shares the same environments as native pentatomid pests. In laboratory conditions we tested T. basalis ability to discriminate between female and male H. halys footprints. We also quantified the walking behaviour of T. basalis when they are rewarded by an oviposition experience on H. halys eggs. The outcomes are discussed by evaluating the possible consequences of alien insect spread on local parasitoid foraging behaviour.