Keywords: 
• dimethoate /
• Caenorhabditis elegans /
• intrinsic rate of natural increase /
• total fertility rate /
• net reproductive rate

Abstract: A hanging-drop method with a semi-fluid culture medium was used to carry out life table experi-ments in order to test the toxic effects of dimethoate on life-cycle traits of Caenorhabditis elegans, after the nematodes were exposed to three groups of dimethoate (0.07, 0.7 and 7 mmol·L^-1, which were 1/1000 LC₅₀, 1/100 LC₅₀ and 1/10 LC₅₀ respectively) for 4 h. The results showed that in 0.7 and 7 mmol·L^-1 groups, the total fertility rates (TFR) of nematodes were 260.60 and 203.80 respectively, both of which decreased significantly compared with control (29923, P<0.05); the net reproductive rates (R₀) were 2403.9 and 147.67, which dropped significantly compared with control (298.67, P<0.05); the intrinsic rates of natural increase (r_m)were 1.342 d^-1 and 1233 d^-1, which were much lower than control (1.387 d^-1, P<0.05); while in 0.07 mmol·L^-1 group, TFR was 293.84, and R₀ was 286.60,the differences of which were not statistically significant (P>0.05). In the scope of the above dimethoate concentration, the values of TFR, R₀ and r_m all decreased evidently as the concentration of dimethoate increased. The study also found that the r_m in 0.07 mmol·L^-1 group was 1.405 d^-1, which was evidently higher than control (P<0.05). From the present study, it was concluded that the fertility of C. elegans decreased when exposed to the dimethoate in a specific amount, while low doses of dimethoate had a hormesis effect on intrinsic rate of natural increase (r_m) of nematode population, and the three parameters of TFR, R₀ and r_m detected in this paper were sensitive to dimethoate exposure in low dosage.