Insecticides Hurt Black Soldier Flies

This is not a major revelation. Insecticides kill insects (hence the name). Black soldier flies are insects. Therefore, insecticides kill black soldier flies, or at least make them sick. This is an important consideration in recycling wastes. Since insecticides are widely used in agriculture, their residues are likely to be found in a variety of substrates. Some insecticide effects have been looked at in the past, but the subject received generally little attention. A recent study contributed to filling the void by investigating the effects of two common pyrethroids on black soldier fly larvae.

Meijer, N., Zoet, L., Rijkers, D., Nijssen, R., Willemsen, M., Zomer, P. and van der Fels-Klerx, H.J., 2024. Toxicity, transfer and metabolization of the pyrethroid insecticides cypermethrin and deltamethrin by reared black soldier fly larvae. Journal of Insects as Food and Feed, https://doi.org/10.1163/23524588-00001167

Reared insects such as black soldier fly larvae (Hermetia illucens) are considered a potential alternative feed protein. However, dietary exposure to insecticide residues via the substrate could adversely affect performance indicators (yield/survival) and substance-transfer from substrate to larval biomass could result in non-compliance with low legal limits. Effects of pyrethroid insecticides cypermethrin and deltamethrin were tested at varying concentrations, with or without the synergist piperonyl butoxide (PBO). Concentration/response curves for yield were estimated and samples were analysed to determine concentrations of parent compounds and selected metabolites. Results suggest that deltamethrin is highly toxic to H. illucens larvae: the critical effect dose for 10% yield loss was estimated to be 0.04 mg/kg, compared to a legal limit in wheat of 2.0 mg/kg. Cypermethrin was comparatively less toxic, in line with prior studies, but may also cause significant adverse effects even for exposure levels below the legal limit – especially when combined with PBO. For both substances, transfer from substrate to larvae is a potential issue due to low limits, and transfer as well as toxicity are increased by presence of PBO. Some metabolites could be detected, but more research is needed to determine resistance mechanisms involved.