Hormesis effects of chlorantraniliprole on a key egg parasitoid used for management of rice lepidopterans

The egg parasitoid Trichogramma japonicum (Hymenoptera: Trichogrammatidae) is used for biological control of lepidopteran pests, and it could be used for optimizing Integrated Pest Management (IPM) in rice crop. Chlorantraniliprole is a diamide insecticide broadly applied for pest control in rice cropping systems and it has been generally considered harm-less to egg parasitoids. However, the impact of sublethal or low lethal concentrations of chlorantraniliprole on T. japonicum remains unclear. In this context, under laboratory conditions we assessed the acute toxicity of chlorantraniliprole on T. japonicum as well as sublethal effects of a low lethal concentration (LC10) on key biological traits of the parasitoid. In addition, we also evaluated the impact of chlorantraniliprole on the biocontrol service provided by T. japonicum on the pest Chilo suppressalis (Lepidoptera: Crambidae) under field conditions. The LC10 of chlorantraniliprole on adult parasitoids through exposure with residues was 0.110 mg/L, and this LC10 induced hormesis in exposed individuals; locomotory activ-ity, respiratory metabolism and mass reproduction of T. japonicum were enhanced. Under field conditions, chlorantranilip- role led to increased biocontrol service provided by T. japonicum (reduced pest damage). These results can be useful for optimizing further the use of Trichogramma parasitoids into IPM in rice crops. It also hints the importance of carrying out careful risk-assessment of pesticide non-lethal effects under field conditions when developing IPM.