ABSTRACT
Objective To understand whether the breeding time of snails influences the evaluation on molluscicidal efficacy against Oncomelania snails so as to make a standardization of methods for screening molluscicides in laboratory. Methods Snails collected from the endemic areas in Nanjing and Tongling cities bred for 1,6,11,16,21.31,61 and 91 days respectively, and then were immersed in 1.000 0,0.500 0,0.250 0,0.125 0,0.062 5 and 0.031 3 mg/L solution of niclosamide for 24 and 48 hours at 25℃ in laboratory. Results One hundred percent killing rate was achieved in the groups of the snails bred for 1 - 11 days and immersed in 1.0 mg/L niclosamide for 24 hours. The LC_(50) concentrations of snails collected from Nanjing, Jiangsu Province and immersed for 24 hours varied from 0.094 7 to 0.133 9 mg/L, and for 48 hours from 0.071 8 to 0.092 6 mg/L.Those of snails collected from Tongling, Anhui Province for 24 hours varied from 0.082 5 to 0.103 9 mg/L, and for 48 hours from 0. 071 8 to 0.082 5 mg/L. The molluscicidal effect was unstable in the groups of snails bred for more than 16 days. There was a significant difference (X_(Nanjing24 h)~2 = 22.26,P