Pyriproxyfen treatment terminates Halyomorpha halys reproductive diapause, with an indirect mortality effect on its egg parasitoid Trissolcus japonicus

The success of Halyomorpha halys (Stal) as an invasive species in temperate climates is partly due to its ability to survive winter in a state of reproductive diapause. In H. halys, the termination of juvenile hormone (JH) production by the corpora allata, in response to a decline in day length, leads to the initiation of diapause and suspension of reproductive activity. Results of this study showed that topical application of the JH analog pyriproxyfen at doses of 0.05-100 mu g per insect resulted in the resumption of oocyte formation and oviposition in a dose-dependent manner, with the ED50 estimated at 1.14 mu g per insect. Eggs induced by pyriproxyfen application had significantly lower hatchability than control eggs. The indirect effects of host exposure to pyriproxyfen on the hymenopteran parasitoid Trissolcus japonicus (Ashmead), a candidate biological control agent of H. halys, were evaluated. When presented with eggs produced by pyriproxyfen-treated females, T. japonicus was observed ovipositing, but no adult parasitoids emerged from host eggs. Exposure to pyriproxyfen has the potential to lower the reproductive potential of H. halys populations by inducing the production of eggs with reduced viability during periods of low resource availability. The complete mortality of T. japonicus developing on pyriproxyfen-induced eggs suggests that insect growth regulators which interfere with host reproduction may exert a strong indirect effect on beneficial egg parasitoids, and may not be compatible with egg parasitoid biological control programs.