Molluscacides

Abstract: This paper records attempts to overcome the problems of using a powerful but non-ovicidal molluscicide (N-tritylmorpholine) in eradicating snails from a dam by treating the water twice in 14 days. The first treatment was aimed at the existing snail population and the second at snails hatched from eggs that survived the first application. At each treatment an over-all concentration of 0.25 ppm was applied by spraying a 16% emulsifiable concentrate of N-tritylmorpholine from shore and boat to the water surface. The snails, Biomphalaria pfeifferi and Lymnaea natalensis, were first seen again 8 weeks from the start of the application in the region of 2 inlet furrows. When pretreatment levels of snails were again reached, a second double treatment was applied, again at an over-all concentration of 0.25 ppm but using a 50% paste formulation applied over 3 days for 3 hours per day to the inlet furrows. The snail kill was again 100% as measured by the sampling technique used but again young snails appeared 9 weeks later. The author concludes that single treatments at 5-week intervals probably represent the best means of control with N-tritylmorpholine.

Abstract: Objective To explore the spatial distribution and elimination of Oncomelania hupensis in mountainous regions.Methods Pnge County in Tezi township was selected as the study site and the quadrates were placed randomly to investigate snail The two sods with water were selected as the sites of snail elimination.One sod with area of 1000 m2 and mean density of 9.88 snails/0.11 m2 was selected as the trial group with 'heaping' method,and the other with area of 1000 m2 and mean density of 9.80 snails/0.11 m2 as the control group with sprinkling method.The molluscacidal effect of the two methods was compared by systematic sampling(5 m×5 m).The sample size was 40 quadrates.Results The snail distributed mainly in the sods with water,canals and farmlands.Among the three snail habitats,the area with snail was the most in the farmlands with relatively lower density of living snail;the next was the sods with water,with relatively higher density of living snail.Before killing snails,the rate of quadrates with snails was 87.50% in the trial site,and 82.50% in the control site.The mortality of snails was 3.89% in the trial site,and 4.16% in the control site.After three months,no living snails were found in the trial site,while in the control site,the rate of quadrates with snails (X2=0.31,P＞0.05) and the mortality of snails (X2=3.12,P＞0.05) did not decrease significantly,and the density of living snails only reduced by 8.88%.Condnsion The 'heaping' method is an efficacious measure for snail control. Key words: Snails; Schistosomiasis; Molluscacides; Program evaluation