Lethal and sublethal effects of chronic exposure to insecticide residues on reared Alphitobius diaperinus

Edible insects such as lesser mealworm (Alphitobius diaperinus) are a promising new protein source for food and feed. The feed substrate on which these insects are reared may be contaminated with residues of insecticides originating from agricultural products that may impact insect performance. In this study, two generations of A. diaperinus were chronically exposed to spinosad (2.0 and 0.2 mg/kg) and imidacloprid (0.1 and 0.01 mg/kg) in the substrate. The aim was to determine sublethal effects on performance measures (total biomass (yield), mean individual weight, number of alive individuals) of larvae, pupae, and adult beetles, as well as pupation and eclosion. Exposure to spinosad at 2.0 mg/kg resulted in significant adverse effects on most performance measures of larvae, of both generations. Imidacloprid caused a reduction in yield and mean individual weight of the larvae as compared to the control at 0.1 mg/kg, while an increase in those measures was observed at 0.01 mg/kg. Significant adverse effects on adult beetles were only observed for imidacloprid at 0.1 mg/kg, and no significant effects of this insecticide on pupation and eclosion were observed. The concentrations of tested substances in larval samples were negligible for both generations, however, transfer from substrate to larval biomass was higher in the offspring generation relative to the parent generation. More research is needed to fully assess the hazard of insecticide residues to cause sublethal effects on A. diaperinus, for which method development for more cost-efficient designs is required.