Lethal and Sublethal Effects of Two Commercial Insecticides on Egg Parasitoids (Hymenoptera: Scelionidae) of Green Stink Bugs (Hem: Pentatomidae)

Pistacia vera L. is one of the most important horticultural crops in Iran. The stink bugs Acrosternum arabicum and Brachynema germari are two of the key pests that cause significant direct and indirect damage on Pistacia vera. Egg parasitoids have been considered as potential biological control agents of pistachio green stink bugs. Among them, Trissolcus semistriatus and Psix saccharicola are the most abundant and efficient parasitoid for A. arabicum in pistachio orchards. In this study, we assessed lethal and sublethal effects of two commonly used insecticide products (fenitrothion and a binary mixture of lambda-cyhalothrin + thiamethoxam) on these two parasitoid wasps under laboratory conditions. The median lethal concentration (LC50) values for fenitrothion and thiamethoxam + lambda-cyhalothrin in P. saccharicola and T. semistriatus were estimated as 1.03, 0.48 and 0.87, 0.98 mg a.i./liter, respectively. In terms of sublethal effects, insecticide treatments altered the type of functional response from type III to type II in T. semistriatus. However, P. saccharicola exhibited a type II functional to density of A. arabicum for all treatments, although attack rates were lower for insecticide-exposed wasps while handling times increased. Our results show that sublethal effects of insecticides further reduce the efficacy of biological control agents. Effective integrated pest management programs should avoid antagonistic interactions between chemical and biological control methods. The results of this study provide useful information to develop comprehensive integrated pest management programs for stink bugs in pistachio orchards.