Sublethal effects of imidacloprid exposure on Spalangia endius, a pupal parasitoid of filth flies

Abstract

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.

Decaying Organic Matter Does Not Remove Sublethal Effects of Imidacloprid on Mating in Spalangia endius (Hymenoptera: Pteromalidae), a Parasitoid of Filth Flies

“…These results contrast with results of the previously described study of parasitization rates of S. endius, where hosts being in media eliminated the negative effect of imidacloprid on parasitization (Burgess et al 2017). The mass per area of imidacloprid that wasps were exposed to in Burgess et al (2017) and in the present study were the same, but the lethality of that exposure is less for the present study.…”

“…These results contrast with results of the previously described study of parasitization rates of S. endius, where hosts being in media eliminated the negative effect of imidacloprid on parasitization (Burgess et al 2017). The mass per area of imidacloprid that wasps were exposed to in Burgess et al (2017) and in the present study were the same, but the lethality of that exposure is less for the present study. Explanations for the effect of media differing in these two studies include: the Illinois strain being less sensitive to imidacloprid, removal by media being sufficient to mitigate imidacloprid's effects on parasitization but not on mating, and burrowing through a larger quantity of media (Burgess et al 2017) removing more imidacloprid than walking on and maybe through a smaller quantity (the present study).…”

“…In a Florida strain of S. endius, survival and subsequent ability to produce progeny and reduce fly numbers was reduced by contact with imidacloprid on a glass surface at concentrations well above recommended application rates (Burgess and King 2015). However, if females then had to move through manure-like media to locate hosts, parasitization ability was no longer affected (Burgess et al 2017). An ELISA (enzyme-linked immunosorbent assay) demonstrated that the media reduced the amount of imidacloprid in-on the parasitoids.…”

A Neonicotinoid Affects the Mating Behavior of Spalangia endius (Hymenoptera: Pteromalidae), a Biological Control Agent of Filth Flies

“…Because of dissemination and breakdown, the concentration that S. endius and other related parasitoids of filth flies encounter on livestock facilities will sometimes be less than this application amount (Mandeville et al 1990, Burgess et al 2018. Individual parasitoids that survive exposure to imidacloprid may nevertheless produce fewer offspring, with more adult flies resulting (Burgess et al 2017).…”

“…Sublethal effects are effects on surviving individuals (Desneux et al 2007). Sublethal effects of imidacloprid on parasitization have been examined in already-mated S. endius (Burgess et al 2017). Parasitization by such females is reduced when hosts are readily accessible, but not when they are buried.…”