[The Molluscicidal Effect of Chlorosalicylicamide Sustained-release Granules on Oncomelania hupensis].

Abstract

Objective: To evaluate the molluscicidal effect of the chlorosalicylicamide sustained-release granules (LDS-SRG) on Oncomelania hupensis.

Methods: Seven effective concentrations or dosages of LDS-SRG, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2 and 6.4 mg/L （for immersion test） or g/m2（for spraying test）, were prepared from the original 5% and 10% concentrations or dosages in the laboratory. In the immersion test, each concentration of LDS-SRG was incubated with 3 packs of snails（30 snails in each pack）, and each pack was taken for snail counting at 24, 48 and 72 h respectively. In the spraying test, each dosage of LDS-SRG was applied to 200 snails, and the snail mortality was calculated in 50 randmoly collected snails on days 3 and 7, and in the whole on day 14 after administration. In the field immersion test, LDS-SRG at concentrations of 0.4, 0.8 and 1.6 g/m3 was incubated with 6 packs of snails （30 snails in each pack）, and each 2 packs were taken at 24, 48, and 72 h to calculate the snail mortality. In the field spraying test, 0.8, 1.6 and 3.2 g/m2 LDS-SRG was sprayed in 3 snail-positive ditches （～100 m2）, and 10 boxes of snails were selected in each ditch on days 3, 7 and 14 to calculate the snail mortality. The 50% wettable powder of niclosamide ethanolamine salt （WPN） with effective concentrations or dosages of 1.0 mg/L （or g/m2 and g/m3） was used as the positive control. Fresh water served as the blank control.

Results: In the labratory immersion test using the original concentration of 5%, both 0.1-6.4 mg/L LDS-SRG for 72 h and 1.6-6.4 mg/L LDS-SRG for 48 h caused 100% mortality; and the concentration lethal to 50% （LC50） at 24, 48 and 72 h was 0.70, 0.01 and 0.01 mg/L respectively. When using the original concentration of 10%, both 0.1-6.4 mg/L LDS-SRG for 72 h and 0.2-6.4 mg/L LDS-SRG for 48 h caused 100% mortality; and the LC50 at 24, 48 and 72 h was 0.15, 0.01 and 0.01 mg/L respectively. The labratory spraying test showed that 7-day administration of 1.6 and 6.4 g/m2 LDS-SRG as well as 14-day administration of 3.2 and 6.4 g/m2 LDS-SRG prepared from 5% dosage, resulted in a snail mortality>95%, with the LD50 on days 3, 7 and 14 being 0.06, 0.16, and 0.18 g/m2; 14-day administration of 1.6 g/m2 LDS-SRG as well as 7-day administration of 6.4 g/m2 LDS-SRG prepared from 10% dosage, resulted in a snail mortality>95%, with the LD50 on days 3, 7 and 14 being 3.29, 0.75, and 0.16 g/m2. The mortality by various dosages of LDS-SRG prepared from 5% dosage was significantly higher than that of the control group (P<0.05). In the field immersion test, the snail mortality by 1.6 g/m3 LDS-SRG prepared from 5% and 10% concentrations for 72 h was 96.43% and 98.21% respectively (P>0.05 versus the control group). In the field spraying test, the snail mortality by 3.2 g/m2 LDS-SRG prepared from 5% dosage for 3, 7 and 14 days was 93.99%, 91.18% and 86.48% respectively, and that from 10% dosage was 94.95%, 93.50% and 85.43%, all significantly higher than that of the control group （82.83%, 72.38% and 48.38%）（P<0.05）; the snail mortality by 0.8 g/m2 LDS-SRG prepared from 5% dosage for 14 days（66.51%） and that by 1.6 g/m2 LDS-SRG prepared from 5% dosage for 3 days（84.61%） were both significantly higher than that by 10% LDS-SRG（20.13% and 43.06%） （P<0.05）.

Conclusion: The 5% and 10% LDS-SRG used separately in the immersion test and the spraying test both meet the requirements of the national standard of Efficacy Test Methods and Evaluation of Molluscicide for Pesticide Registration.