Abstract: 【Aim】 Due to improper application of pesticides, environmental pollution has become an important obstacle to the development of sericulture. This study aims to assess the effects of field application of the organophosphorus pesticide dimethoate on the silkworm, Bombyx mori, so as to elucidate its damage mechanism to the gonads of this insect. 【Methods】 According to the LD₅₀ value of dimethoate to B. mori larvae (400 mg/L) reported in the literature, the 5th instar larvae of B. mori were fed with mulberry leaves that had been soaked in different concentrations (0, 50, 100, 200 and 400 mg/L) of dimethoate solution. After treatment with dimethoate, the cocoon quality and body weight of the 5th instar larvae, and the residual content of dimethoate and the H₂O₂ content, the activities of antioxidant enzymes and the mRNA expression levels of these enzymes in the gonads of both male and female larvae were determined. 【Results】 The results showed that the cocoon quality and body weight of the 5th instar larvae of B. mori and the residual content of dimethoate in the gonads of both female and male larvae after treatment with dimethoate showed the concentration-effect relationship. The H₂O₂ content in the gonads of both female and male larvae treated with 100-200 mg/L dimethoate significantly increased as compared with that in the control (treated with water). With the increase of the concentration of dimethoate, both SOD and CAT activities showed a trend of decreasing first and then increasing, and both of them were lower than those in the control group. And there was a positive correlation between the SOD or CAT activity and the mRNA expression levels of the corresponding gene. After HE staining and in vitro culture of the spermatogenic sac of the silkworm, the morphological structure of gonads in male and female larvae after treatment with dimethoate showed obvious change, with their morphology abnormal, intracellular vacuoles increased, and the number of germ cells reduced relatively. Besides, with the increase in the concentration of dimethoate, its damage to gonads became more serious. 【Conclusion】 The results of this study suggest that using leaves that have been soaked in dimethoate solution at a concentration below LD₅₀ to feed the 5th instar larvae of B. mori have toxic effects on the development of gonads of B. mori, and this provides a basis for banning the use of dimethoate in the field and strengthening the regional management of agricultural production.

Key words:  Bombyx mori')"> Bombyx mori, dimethoate, reproductive toxicity, oxidative stress, morphological structure