Insights into the effect on silkworm (Bombyx mori) cocooning and its potential mechanisms following non-lethal dose tebuconazole exposure

Silkworm (Bombyx mori) is one of the most important economic insects in the world, while pesticides impact its economic benefits. Tebuconazole is a fungicide that has been frequently detected in agriculture systems at concentrations that affect endocrine function in organisms. In the present study, silkworm larvae at different instar stages were exposed to tebuconazole, respectively. Cocoon weight, cocoon shell weight and cocoon shell rate were significantly decreased by 6.8%, 11.8% and 4.4% respectively, after exposure to 0.40 mg/L tebuconazole at 2nd -3rd instar stage. Vacuolization was found in the exposure silkworm under histopathological study at all stages exposures, indicating potential damage to silk gland. Downregulation of genes transcription (Fibh, Fibl, P25, Ser2, Ser3) involved with protein synthesis in the silk gland were further observed, and the results showed significant decreasing in mRNA expression among the tebuconazole treatments. Ecdysteroid levels in silkworm were changed with pronounced decreases after exposed to tebuconazole. In contrast, exposure to tebuconazole significantly increased juvenile hormone 1 concentrations and the maximum increasing fold of juvenile hormone 1 was up to 3.73 which was observed at stage I exposure. In addition, co-exposure to 2 and 10 mg/L forskolin able to mitigate tebuconazole-induced downregulate of mRNA expression of Sgf1 in the present study, indicating the potential mechanism of tebuconazole-induced chronic toxicity in silkworm may relative to PI3K/AKT/TORC1/Sgf1 pathway.