Evaluation of imidacloprid (Confidor OD®) genotoxicity in Chrysoperla externa eggs (Neuroptera: Chrysopidae) through comet assay

Abstract

The comet assay allows the analysis of DNA damage caused by different genotoxins. This assay has recently gained interest because of its ease of studying the interactions of xenobiotics with different organisms.Chrysoperla externa (Hagen, 1861) is a species of great economic relevance because it is a predator of major agricultural pests during its larval stage. Neonicotinoids are the most important chemical class of insecticides introduced into markets. A previous imidacloprid toxicity assessment on C. externa showed that this neonicotinoid insecticide reduced the egg viability. The objective of this study was to analyze the genotoxicity of Confidor OD® (imidacloprid 20% a.i., LS, Bayer CropScience) on the biological control agent C. externa at DNA level using the comet assay as an ecotoxicological biomarker. A comet assay protocol has been developed for this species at first time. For the bioassays, the commercial product formulated Confidor OD® was used at two concentrations: 100 and 180 mg/l of the active ingredient. Selected eggs were dipped in a Confidor OD® solution for 15 s. Descriptors evaluated in the comet assay were damage index, % DNA damage, and tail length. The damage index did not show any significant differences between the different concentrations evaluated, but differences were observed for tail length, because at higher concentrations of Confidor OD®, there were greater DNA breaks. The DNA of the cells from treated eggs analyzed at 48 h and 96 h of development showed the same % DNA damage; that is, they had no recovery capacity. Application of Confidor OD® to C. externa eggs produced irreparable breaks at the DNA level. The technique adjusted for C. externa can be used in other beneficial insects to study pesticide genotoxicity using a comet assay.