Comparative ecotoxicity of neonicotinoid insecticides to three species of Trichogramma parasitoid wasps (Hymenoptera: Trichogrammatidae)

Abstract

Compatibility of neonicotinoid insecticides with the natural enemies has been concerned for decades. This study aims to evaluate and compare the acute and sublethal toxicity effects of neonicotinoid insecticides on three species of Trichogramma parasitoid wasps (i.e. Trichogramma dendrolimi, T. ostriniae and T. confusum) with broad distribution and great relevance to integrated pest management (IPM) strategies. A residual contact bioassay demonstrated that nitenpyram had the greatest intrinsic toxicity to T. dendrolimi and T. ostriniae with LC₅₀ values of 0.060 (0.056-0.065) and 0.066 (0.050-0.087) mg a.i. L^-1, respectively. But for T. confusum, the most toxic neonicotinoid insecticide is dinotefuran with a LC₅₀ value of 0.065 (0.055-0.078) mg a.i. L^-1. Furthermore, based on the risk quotient estimation, acetamiprid was considered to be the only safe neonicotinoid insecticide (Class 1, RQ＜50). A dipped egg contact bioassay showed that neonicotinoid insecticides induced significant toxic effects on the parasitism of three Trichogramma spp. at low-lethal concentrations. Additionally, emergence probability of the unexposed offspring was also significantly reduced by neonicotinoids. According to the estimated EC₅₀ values, acetamiprid possessed the least toxicity to the parasitism and emergence of T. dendrolimi and T. ostriniae, and for T. confusum, the least toxic neonicotinoid insecticide was thiacloprid. Overall, among the test neonicotinoid insecticides, acetamiprid and thiacloprid may exhibit the less ecotoxicity to the test Trichogramma species.

Keywords: Neonicotinoid; Parasitoid wasp; Risk assessment; Sublethal effect; Trichogramma species.