Insecicide Residues Are Bad for Larvae

Since black soldier flies are insects, it is not much of a revelation that insecticides are not good for them. Insecticides are widely used in agriculture; therefore, their residues are often present in harvested commodities. Food safety regulations set residue levels that are supposedly safe for humans and other animals. However, as an article below demonstrates, these levels may have a negative effect on black soldier fly larvae. This must be kept in mind when sourcing waste streams for larval farming.

Meijer, N., Zoet, L., de Rijk, T., Zomer, P., Rijkers, D., van der Fels‐Klerx, H.J. and van Loon, J.J., 2023. Effects of pyrethroid and organophosphate insecticides on reared black soldier fly larvae (Hermetia illucens). Insect Science https://doi.org/10.1111/1744-7917.13269

Black soldier fly larvae (Hermetia illucens) receive growing interest as a potential alternative animal feed source. These insects may be exposed to insecticide residues in the rearing substrate. This study aimed to investigate the effects of six different pyrethroid and organophosphate insecticides on this insect species’ performance. The toxicity of two “model” substances for each of these classes (cypermethrin; pirimiphos-methyl) was quantified, with and without the synergist piperonyl butoxide (PBO). Critical effect doses corresponding to 10% yield (CED10) for cypermethrin (0.4 mg/kg) and pirimiphos-methyl (4.8 mg/kg) were determined. The addition of PBO to cypermethrin enhanced its relative potency with a factor 2.6. These data were compared against the relative toxicity of two analogue substances in each class (permethrin, deltamethrin; chlorpyrifos-methyl, malathion). Results suggest that exposure to concentrations complying with legal limits can cause significant reductions in yield. Exposure to multiple substances at lower concentrations resulted in negative additive and synergistic effects. Of the tested substances, deltamethrin was most toxic, causing 94% yield at 0.5 mg/kg. Analytical results suggested that transfer of tested substances to the larval biomass was substance- and concentration-specific, but appeared to be correlated to reduced yields and the presence of PBO. Transfer of organophosphates was overall low (<2%), but ranged from 8% to 75% for pyrethroids. Due to very low limits in insect biomass (∼0.01 mg/kg), high transfer may result in noncompliance. It is recommended that rearing companies implement lower contractual thresholds, and that policymakers consider adjusting legally allowed maximum residue levels in insect feed.