Abstract: To examine the enzyme activities and corresponding gene expressions under the stress of cadmium in the lepidopteran model insect, Bombyx mori, which may be used as a bioindicator to monitor heavy metal pollution. 【Methods】 B. mori larvae were exposed to Cd²⁺ in the whole larval stage, the malondialdehyde (MDA) content, and the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) as well as their corresponding mRNA levels in the fat body of the 5th instar larvae of both sexes were evaluated. 【Results】 The MDA contents in the fat body in male and female larvae of the silkworm significantly changed in a concentration-dependent manner, increasing with the Cd²⁺ concentration. The activities of both SOD and CAT increased at low exposure dose, which protected silkworms from oxidative stresses. However, the activities of SOD and CAT successively decreased after exposure to high dose of Cd²⁺. According to the analysis of Pearson correlation, the SOD activities were positively correlated with the CAT activities (male: R=0.770,  P=0.001; female: R=0.854,  P=0.000). The CAT activities and its mRNA expression levels showed positive correlations in the fat body in females (R=0.712, P=0.003). The GSH-Px activities in the fat body in males changed in a concentrationdependent manner, increasing with the Cd²⁺ concentration, and those in females exposed to 12.5-50 mg/kg Cd²⁺ were significantly higher than the control (P<0.05). The changes of the GSH-Px actity and its mRNA level showed positive correlations (R=0.834, P=0.000). However, the GSH-Px activities in females increased at low exposure dose, and those in females exposed to 12.5 mg/kg Cd²⁺ were significantly higher than the control (P<0.01). 【Conclusion】 These results show that acute exposure of the silkworm to Cd²⁺ has the toxic effect on its fat body, and this might be related to the increase in lipid peroxidation and the changes of the antioxidative enzyme activities. The results also suggest that detoxifying strategies in the silkworm against Cd²⁺ exposure seem to be sex-dependent.

Key words:  Bombyx mori, heavy metal pollution, cadmium, fat body, malondialdehyde, antioxidant enzyme, enzyme activity, mRNA expression