Experimental study on the resistance of Oncomelania snails to niclosamide

Objective To study whether Oncomelania snails developed resistance to niclosamide after its long-term use in fields.Methods Snails in the experimental group were captured from the area where niclosamide was used long-term while snails in the control group were captured from an area where niclosamide was never used;the two areas were both located in Xuba Township,Tongling County,Anhui Province.Different concentrations of niclosamide,i.e.2.0000,1.0000,0.5000,0.2500,0.1250,0.0625,and 0.0313 mg/L,were prepared,and snails in the two groups were immersed in solutions of niclosamide at(24±1) ℃ in the laboratory.The snail mortality rate and the 50% lethal concentration(LC50) were observed.Results The LC50 for niclosamide used on the experimental group for 24,72,and 120 hours was 0.337,0.175,and 0.136 mg/L,respectively,while the LC50 for niclosamide used on the control group for 24,72,and 120 hours was 0.165,0.090,and 0.061 mg/L,respectively.Values for the former were markedly higher than those for the latter.The snail mortality rate in the experimental group was much lower than that in the control group when the concentration of niclosamide was from 0.0625 to 0.0250 mg/L.Conclusion Oncomelania snails may have developed resistance to niclosamide after its long-term use in fields.