Evaluation of a new molluscicide for counteracting the intermediate snail host of Schistosoma japonicum

A novel molluscicide, derived from niclosamide, the salt of quinoid-2',5-dichloro-4'-nitrosalicylanilide (LDS) was recently developed in China. The molluscicidal activity of LDS was compared with the commonly used molluscicide niclosamide (WPN) by immersion at seven concentrations; 0.05, 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 mg/L, and with spraying and powdering methods (dosages of 0.2, 0.4, and 0.8 g/m(2)) in the laboratory and the field. We recorded mortality at 1 d, 3 d, and 7 d. The results showed that at 0.4 mg/L immersion exposure for 72 hours, snail mortalities for LDS and WPN were 100% and 96.70% respectively in the lab, and 100% and 95.33 +/- 1.15% respectively in the field. With a dosage of 0.8 g/m(2) exposure for 7 d by spraying, snail mortalities for LDS and WPN were 100% and 97.33 +/- 2.30% respectively in the lab, and 99.27 +/- 1.27% and 97.47 +/- 3.11% in the field. With a dosage of 0.8 g/m(2) exposure at 7 d by powdering, snail mortalities for LDS and WPN were both 98% in the lab, and 100% in the field. These results from three different methods show that molluscicidal effects were similar in the lab and the field. However, LDS is much cheaper than WPN, and LDS is less toxic to fish than WPN. Therefore, LDS might be more useful than WPN for controlling snails in endemic areas of schistosomiasis in China.