The silkworm (Bombyx mori) alleviates the toxic effects of the novel meta-diamide insecticide broflanilide by modulating its midgut immune system

Abstract

Due to the development of resistance in pests to the first two generations of noncompetitive antagonists (NCAs), broflanilide, a novel meta-diamide insecticide targeting the γ-aminobutyric acid receptor (GABAR) in pests, has been widely used in many countries. However, the improper use of broflanilide can result in its residue accumulating in agricultural environments, posing a potential threat to the sericulture industry. In this study, we measured biological parameters of silkworms and found that exposure to sublethal doses of broflanilide significantly inhibited the development, silk yield, and reproduction of silkworms. Meanwhile, we also measured the H₂O₂ content, antioxidant enzyme activities, and MDA levels in the midgut of silkworms. The results indicated that sublethal doses of broflanilide induced oxidative stress in the silkworm midgut and caused tissue damage. In addition, we measured the expression levels of immune-related signaling pathway genes in the silkworm midgut using qRT-PCR. The results showed that broflanilide significantly increased the expression levels of genes in the TOLL, immune deficiency (IMD), and JAK/STAT signaling pathways, as well as antimicrobial peptide genes. This suggests that immune regulation in the midgut may help silkworms resist the toxicity of broflanilide. Finally, through age-stage two-sex life table analysis, we found that broflanilide reduced the life table parameters (s_xj, e_xj, and l_x) of the F₁ generation silkworms. This indicates that broflanilide has transgenerational effects on silkworms. In summary, broflanilide exerts multiple adverse effects on silkworms and their offspring, while silkworms can mitigate the toxicity of broflanilide through immune regulation in the midgut.