Effects of novaluron exposure on gene expressions in midgut of silkworm, Bombyx mori

The silkworm, Bombyx mori , is a vital economic insect and a lepidopteran model organism whose survival and silk production are entirely dependent on mulberry leaves. Long-term domestication has diminished its stress tolerance, rendering it susceptible to pesticide residues. Novaluron, a benzoylurea insect growth regulator, disrupts insect development by inhibiting chitin synthesis. However, the effects of novaluron exposure on the midgut structure, as well as digestive and detoxification functions in silkworm, remain unreported. This study investigated the effects of trace novaluron exposure (0.001 mg/L) on the midgut structure and function of Bombyx mori by using histopathological analysis, quantitative real-time polymerase chain reaction (qRT-PCR), and enzyme activity assays. Results showed severe midgut damage, including muscular layer rupture, cellular disorganization, and extensive degradation of the peritrophic membrane. Transcript levels of digestion-related genes ( α-amylase , trypsin-like protease , lipase 1 ) and oxidative phosphorylation genes ( NDUFB7 , NDUFV1 ) were significantly downregulated, indicating impaired digestion and energy metabolism. Antioxidant gene expression ( SOD , CAT , GST , GPX ) was dysregulated, and chitin synthase genes ( BmCHSA , BmCHSB ) were markedly suppressed. In contrast, detoxification genes ( CYP9a19 , CarE9 ) were upregulated, accompanied by increased activities of GST, cytochrome P450 enzymes (CYPs), and carboxylesterase (CarE). In summary, novaluron exposure damages midgut structure, disrupts digestive and metabolic functions, weakens antioxidant defenses, and activates detoxification responses. This work provided mechanistic insights into novaluron toxicity in Bombyx mori and a basis for further toxicological investigation.