Chemical signals mediating interactions between Galeruca tanaceti L. (Coleoptera, Chrysomelidae) and its egg parasitoid Oomyzus galerucivorus (Hedqvits) (Hymenoptera, Eulophidae)

Chemical signals mediating interactions between Galeruca tanaceti and its egg parasitoid Oomyzus galerucivorus (Hymenoptera, Eulophidae) were studied. Neither odor of gravid females of G. tanaceti nor volatiles of their feces were attractive to the parasitoid, However, the presence of the beetles' feces on a substrate arrested the parasitoid and elicited frequent antennal drumming. Thus, feces may contain a kairomone important for host finding. Odors of damaged and undamaged host plants had no effect on the parasitoids, O. galerucivorus did not detect its host eggs at close range but encountered them by chance. Neither the structure nor the dark color of the egg surface play a key role in host recognition, but chemicals of the extrachorion which could be isolated by dichloromethane. Fractionation of the dichloromethane extract by TLC revealed a single active fraction which induced host recognition behavior. Since rite eggs of G. tanaceti contain anthraquinones and anthrones which are active as feeding deterrents against predators, we hypothesized that reproductive success of O. galerucivorus is due to sequestration of these protective compounds. However, GC-MS analyses revealed that there was no transfer of them from the host egg into the adult parasitoid.