Tolerance and degradation of the insecticide pirimiphos-methyl and its metabolites by black soldier fly and yellow mealworm larvae

Abstract Insect farming is gaining increasing attention because of the ability of insects to upscale a variety of waste and by-product biomass efficiently into proteins and lipids. In the European Union and in Norway, the use of insects is permitted in formulated pig, poultry, and fish feeds and more recently for human consumption. However, the European Food Safety Authority has highlighted the lack of data regarding the safety of processing pesticide-contaminated biomass by insects into feed or food products. Secondly, the presence of insecticide residues in plant biomass might negatively affect the growth or survival of the insects themselves. This study aimed to evaluate the fate of the insecticide pirimiphos-methyl (PM) in black soldier fly ( Hermetia illucens , BSF) and yellow mealworm ( Tenebrio molitor , YMW) larvae composting. PM is a dominant pesticide found in relevant insect biomasses. Newly hatched larvae were fed on a standard poultry feed substrate spiked with pirimiphos-methyl at different concentrations: 10, 20, and 40 mg/kg (wet base), under optimal breeding conditions. Poultry feed substrate spiked with methanol served as control group. When the feeding media were spiked with 20 and 40 mg/kg of PM, the survival of both BSF and YMW larvae decreased. Mean larvae mass for both species was reduced with increasing concentrations of PM. PM and 7 compounds were identified in a metabolites/transformation product screen that was aided by in silico predictions. One compound, dihydroxy-PM was uniquely detected in larvae. Neither insect species appears to accumulate PM metabolites, and 90% of PM was metabolised. Results indicate that these insects can be reared on PM-contaminated biomass without risk of PM accumulation.