[Molluscicidal activity of 25% wettable powder of pyriclobenzuron sulphate against Oncomelania hupensis robertsoni ].

Objective: To evaluate the molluscicidal activity of a novel molluscicide pyriclobenzuron against Oncomelania hupensis robertsoni in the mountain regions of Yunan Province, and test its toxicity to fish, so as to provide scientific evidence for the extensive application of this molluscicide in schistosomiasis-endemic foci of Yunan Province.
Methods: In the laboratory and snail-breeding field of Dali Prefecture, Yunnan Province, the molluscicidal activity of 5% wettable powder of pyriclobenzuron sulphate (25% PBU) against O. hupensis robertsoni was assessed by using the immersion and spraying method, and the acute toxicity of 25% PBU to carp fries was tested, while 25% wettable powder of niclosamide ethanolamine salt (50% WPNES) served as a control.
Results: The 1-, 2- and 3-day 25% PBU LC50 and LC90 values were 0.47, 0.25 and 0.23 mg/L, and 1.54, 0.61 and 0.49 mg / L for O. h. robertsoni by using the immersion method in laboratory, and immersion with 25% PBU at 1.0 mg / L for 1 day achieved a comparable molluscicidal efficacy in relative to 50% WPNES at 1.0 mg/L. Spraying with 25% PBU at 4.0 g/m ² achieved 1-, 3- and 7-day snail mortalities of 64.23%, 96.67% and 100.00% in laboratory, respectively, which were not significantly different from those caused by treatment with 50% WPNES at 1.0 g/m ² (all P values > 0.05). One-day field immersion with 25% PBU at doses of 1, 2 and 4 g/m ³ resulted in snail mortalities of 90.00%, 93.33% and 100.00%, respectively, which were not significantly different from those caused by treatment with 50% WPNES at 1.0 g/m ³ (all P values > 0.05), and 3-day field spraying with 25% PBU at doses of 2.0 and 4.0 g/m ² caused snail mortalities of 86.36% and 87.72%, respectively, which were not significantly different from those caused by 50% WPNES treatment (both P values > 0.05). The 24-, 48- and 72-hour LC50 values of 25% PBU to carp fries were 29.38, 24.62 and 23.38 mg/L, respectively, and no fish death was observed within 72 hours of exposure to 25% PBU at a concentration of 17.5 mg/L and lower.
Conclusions: 25% PBU is a novel, highly potent and environment-friendly molluscicide that is feasible in fish ponds, and the recommended dose is 1 g/m ³ for field immersion and 2 g/m ² for field spraying in schistosomiasis-endemic areas of Yunnan Province.