Abstract: To explore the metabolic pathway of NaF in the silkworm, Bombyx mori, the 5th instar larvae of the fluoride-resistant silkworm strain (T6) and the fluoride-susceptible strain (734) were fed on mulberry leaves soaked in 50, 100, 200 and 400 mg/kg NaF solutions, respectively, for 1-7 d, and the activities of carboxylesterases (CarE) and esterases in the midgut were examined. The results showed that the CarE activity in strain 734 was 1.21-1.98-fold as high as that in the control group, while the CarE activity in strain T6 was 0.72-1.10-fold as high as that in the control group. In both strains treated with NaF, the change trend of the esterase activity was similar with the control group within 7 d, and the esterase activity in the two strains was also similar. When the two silkworm strains were treated by NaF at the same concentration, their esterase activities on different days after treatment were significantly different （P＜0.05）. It is inferred that fluoride can increase the CarE activity in the midgut of the fluoride-susceptible strain of the silkworm, and inhibit the CarE activity in the midgut of the fluoride-resistant strain, but it has little effect on the esterase activity in the midgut of both strains of the silkworm.

Key words: Bombyx mori, fluoride, midgut, carboxylesterase, esterase, enzyme activity