Abstract: Objective To observe the efficacy of 50% wettable powder of niclosamide ethanolamine salt(WPNES) in killing Oncomelania hupensis by immersion method for the feasibility in snail control in cold seasons. Methods Outdoor observational group (-2-10°C) and indoor control group (19-25°C) were set to observe the effect of 50% WPNEs on snail killing by immersion technique in winter. The two groups were composed of 6 subgroups of concentrations by effective agent use(ranging from 1.000 0 mg/L, 0.500 0 mg/L, 0.250 0 mg/L, 0.125 0 mg/L, 0.062 5 mg/L to 0.031 3 mg/L) and a blank control group treated by dechlorination water. Mortality and LC50 of snails at 24, 48 and 72 hours in each group were observed and calculated. Results Mortality rates of snails exposed to various concentrations for 24, 48 and 72 h were lower in the outdoor observational group than in the indoor control group, yet LC50 tended to be approximate between the two groups with prolonged exposure time. By the exposure time at 72 h, the mortality rate of snail in outdoor observational group reached 100.00% at the concentration of 1.000 0 mg/L50 %WPNES, and the LC50 was 0.153 3 mg/L. This molluscicidal effect had met the requirements specified in NY/T 1617—2008 Efficacy test methods and evaluation of molluscicide for pesticide registration(Agricultural Industry Standard of the People's Republic of China). Conclusion The molluscicidal efficacy by immersion method using 50% WPNES under low temperature in winter season can meet the requirements of the industry standard, whereas the effect under field conditions needs to be further verified.

Key words: Niclosamide, Immersion method, Winter, Oncomelania hupensis