Evaluation of tolerance to λ-cyhalothrin and response of detoxification enzymes in silkworms reared on artificial diet.

A representative silkworm rearing mode of Ⅰ-Ⅲ instars reared on artificial diet and Ⅳ-Ⅴ instars reared on fresh mulberry leaves has been recognized in some sericultural areas of China. Under this rearing mode, silkworms are prone to be poisoned by pesticide residues on mulberry leaves at the Ⅳ and Ⅴ instar stages. As one of the most widely applied insecticides, λ-cyhalothrin was used to study the insecticide tolerance of silkworm reared on artificial diet (referred as the AD group). Our results showed that the newly ecdysized Ⅳ instar larvae in the AD group were less tolerant to λ-cyhalothrin compared to the mulberry leaves reared group (referred as the ML group). After continuous exposure to trace λ-cyhalothrin, the weight gain and the survival rate of silkworms were significantly lower in the AD group than those in the ML group, even though compensatory growth was observed in the control of the AD group. Histopathology and ultrastructure of fat body showed that λ-cyhalothrin induced more severe cell injuries in the AD group, such as shrunken nucleus, dilatation of endoplasmic reticulum, and mitochondrial swelling. The transcription levels of detoxification related genes (CYP4M5, CYP6AB4, CarE2, CarE5, GSTe1 and GSTe3) and the enzyme activities of P450s, CarEs and GSTs were inducible by trace λ-cyhalothrin in a time-specific manner, and the data showed that the response of P450 enzyme activity was retarded in the AD group, indicating a potential reason for a higher sensitivity to λ-cyhalothrin. Our results provided a new clue for the study of the relationship between feed nutrition and detoxification ability, and also provided an important reference for the development of modern silkworm rearing mode.