Comprehensive safety assessment of Bt toxins Cry1Ac or Cry2Ae on the non-target insect Hermetia illucens, a natural waste recycler

The widespread cultivation of transgenic crops expressing Bacillus thuringiensis (Bt) proteins generates substantial amounts of crop residues, raising the need for sustainable management strategies. The black soldier fly (BSF), Hermetia illucens, is a promising candidate for the bioconversion of organic wastes due to its high feeding rate, efficient nutrient conversion, and economic value. However, the potential effects of Bt toxins on this non-target species remain poorly understood. Therefore, we evaluated the impacts of two widely deployed Bt toxins, Cry1Ac and Cry2Ae, on larval toxicity, development and adult fecundity of H. illucens in this study. Results demonstrated that exposure to Cry1Ac or Cry2Ae at concentrations far exceeding typical levels in transgenic crops did not significantly affect larval survival, growth, developmental duration, pupation, or adult emergence. Similarly, adult reproductive metrics such as mating rate, oviposition, and egg hatchability showed no significant difference from control groups. Transcriptomic analysis of larvae chronically fed Cry1Ac or Cry2Ae revealed only a limited set of differentially expressed genes, indicating minimal molecular perturbation. Furthermore, the effects of a commercial multi-toxin formulation G033A on H. illucens were evaluated. Although treatment with extremely high concentration of G033A resulted in a slight reduction in larval survival, the survival rate remained above 90%, and no significant impacts were observed on other measured parameters. These comprehensive findings demonstrate that H. illucens is highly tolerant to both individual and combined Bt toxins, supporting its potential for the sustainable management of organic matter e.g., Bt crop residues and substantially contributing to the non-target organism biosafety assessment of Bt toxins.