Sublethal effects of imidacloprid exposure on <Emphasis Type="Italic">Spalangia endius</Emphasis>, a pupal parasitoid of filth flies

Parasitoids and neonicotinoids can both suppress economically harmful filth fly populations. However, sublethal effects of neonicotinoids have not previously been studied for commonly used species of filth fly parasitoids. Exposure to an LC₅₀ of imidacloprid decreased the ability of surviving individuals of the parasitoid wasp Spalangia endius Walker (Hymenoptera: Pteromalidae) to kill house fly pupae under some conditions. In an unburied-hosts experiment, significantly more flies and fewer parasitoids emerged in the LC₅₀ imidacloprid treatment versus the LC₁₀ or controls. Parasitoid sex ratio and longevity were not affected. However, in a buried-hosts experiment, parasitoid and fly emergence were independent of treatment. ELISA (enzyme-linked immunosorbent assay) showed lower imidacloprid residues in or on parasitoids exposed to the media in which hosts were buried. Our findings suggest that substrate may reduce pesticides on biological control agents that burrow, making them more effective.