Abstract:

Objective To evaluate the molluscicidal effect of wettable powder of pyriclobenzuron sulphate (WPPS) and its toxicity to fish in marshland schistosomiasis epidemic areas, so as to provide scientific evidence for the extensive application of this molluscicide in marshland schistosomiasis epidemic areas. Methods Six pilot sites in the marshland around Poyang Lake were selected and all obstacles within these sites were removed. The natural mortality of Oncomelania was calculated. The 25% wettable powder of pyriclobenzuron sulphate(WPPS) was dissolved in water to a final concentration of 1, 2, 4, 8 g/m³. The commonly used molluscicidal drug niclosamide ethanolamine salt(WPNES) was dissolved in water to a final concentration of 1 g/m³. Then these formulated molluscicidal drugs in different concentration were sprayed on the different spots of marshland evenly. The control spot was sprayed with water only. The Oncomelania were collected and examined for their viability by crushing the snails 1, 3 and 7 days after administration of the drugs. To test the toxicity of the molluscicidal drugs to fish, a water area in Hubei Province was selected and separated into 6 chambers. Total 30 carp fishes were put into each chamber and adapt for 1 day before administration with WPPS to the final concentration of 2.5, 5.0 and 7.5 g/m³. The control chamber was administrated with WPNES to 2 g/m³. The blank control chamber was added with clean water only. The survival rate of carp was counted and recorded after administration with the drugs for consecutive three days. Results The adjusted mortality of Oncomelania in each group was more than 85% after administration with molluscicidal drugs for 1 and 3 days. The mortality of Oncomelania 3 days after administration with 1 g/m³, 2 g/m³ WPPS(93.1%, 95.0%)was higher than that with drugs for 1 day(88.2%, 90.9%). The adjusted mortality of Oncomelania after administration with 4 different concentrations of WPPS (1, 2, 4, 8 g/m³) were 90.4%, 90.0%, 90.3% and 89.8%, respectively, all higher than that using 1 g/m² WPNES(76.0%) with significant difference (P < 0.05). The adjusted mortality of Oncomelania was higher than 90% at 1 day, 3 days and 7 days when 2 g/m² WPPS was administrated with highest of 94.7% at 3 days. The fish toxicity test results showed that the mortality of carp at 2.5 g/m³, 5.0 g/m³ of WPPS was similar to that of the blank control (0, 3.3%, 6.9%). The mortality of carp was 50% when WPPS was added to 7.5 g/m³ for 2 and 3 days. Chi-square analysis of mortality of carp at 2.5, 5.0, 7.5 g/m³ WPPS was significantly different(P < 0.05). Conclusion WPPS can effectively kill Oncomelania and has high biological safety for fish, so it can be applied in the environment of marshland, fish pond to effectively control Oncomelania, providing an effective alternative molluscicides in marshland schistosomiasis epidemic areas.

Key words: Schistosomiasis, Pyriclobenzuron, Molluscicidal effect, Fish toxicity