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Objective To establish a snail control approach for spraying chemicals with drones against Oncomelania hupensis in complex snail habitats in hilly regions, and to evaluate its molluscicidal effect. Methods The protocol for evaluating the activity of spraying chemical molluscicides with drones against O. hupensis snails was formulated based on expert consultation and literature review. In August 2022, a pretest was conducted in a hillside field environment (12 000 m2) north of Dafengji Village, Dacang Township, Weishan County, Yunnan Province, which was assigned into four groups, of no less than 3 000 m2 in each group. In Group A, environmental cleaning was not conducted and 5% niclosamide ethanolamine salt granules were sprayed with drones at a dose of 40 g/m2, and in Group B, environmental cleaning was performed, followed by 5% niclosamide ethanolamine salt granules sprayed with drones at a dose of 40 g/m2, while in Group C, environmental cleaning was not conducted and 5% niclosamide ethanolamine salt granules were sprayed with knapsack sprayers at a dose of 40 g/m2, and in Group D, environmental cleaning was performed, followed by 5% niclosamide ethanolamine salt granules sprayed with knapsack sprayers at a dose of 40 g/m2. Then, each group was equally divided into six sections according to land area, with Section 1 for baseline surveys and sections 2 to 6 for snail surveys after chemical treatment. Snail surveys were conducted prior to chemical treatment and 1, 3, 5, 7 days post-treatment, and the mortality and corrected mortality of snails, density of living snails and costs of molluscicidal treatment were calculated in each group. Results The mortality and corrected mortality of snails were 69.49%, 69.09%, 53.57% and 83.48%, and 68.58%, 68.17%, 52.19% and 82.99% in groups A, B, C and D 14 days post-treatment, and the density of living snails reduced by 58.40%, 63.94%, 68.91% and 83.25% 14 days post-treatment relative to pre-treatment in four groups, respectively. The median concentrations of chemical molluscicides were 37.08, 35.42, 42.50 g/m2 and 56.25 g/m2 in groups A, B, C and D, and the gross costs of chemical treatment were 0.93, 1.50, 0.46 Yuan per m2 and 1.03 Yuan per m2 in groups A, B, C and D, respectively. Conclusions The molluscicidal effect of spraying 5% niclosamide ethanolamine salt granules with drones against O. hupensis snails is superior to manual chemical treatment without environmental cleaning, and chemical treatment with drones and manual chemical treatment show comparable molluscicidal effects following environmental cleaning in hilly regions. The cost of chemical treatment with drones is slightly higher than manual chemical treatment regardless of environmental cleaning. Spraying 5% niclosamide ethanolamine salt granules with drones is recommended in complex settings with difficulty in environmental cleaning to improve the molluscicidal activity and efficiency against O. hupensis snails.
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Objective To evaluate the molluscicidal effect of 25% wettable powder of pyriclobenzuron sulphate (WPPS) against Oncomelania snails in hilly schistosomiasis-endemic regions and test its toxicity to fish. Methods In October 2020, a snail-infested setting which had been cleared was selected in Nanjian County, Yunnan Province and divided into several blocks, and the natural snail mortality was estimated. 25% WPPS was prepared into solutions at concentrations of 1 and 2 g/L, and 25% wettable powder of niclosamide ethanolamine salt (WPNES) was prepared into solutions at a concentration of 2 g/L. The different concentrations of drugs were sprayed evenly, and the same amount of water was used as blank control. Snails were surveyed using the systematic sampling method 1, 3 and 7 days post-treatment, and snail survival was observed. A fish pond was selected in Nanjian County, and 2 kg 25% WPPS was evenly sprayed on the water surface to allow the effective concentration of 20 g/L. Fish mortality was estimated 8, 24, 48 and 72 h post-treatment. Results One-day treatment with 1 and 2 g/L WPPS and 2 g/L WPNES resulted in 97.99%, 97.99% and 94.11% adjusted snail mortality rates (χ2 = 3.509 and 3.509, both P values > 0.05), and the adjusted snail mortality was all 100% 3 d post-treatment with 1 and 2 g/L WPPS and 2 g/L WPNES, while 7-day treatment with 1 and 2 g/L WPPS and 2 g/L WPNES resulted in 91.75%, 86.57% and 57.76% adjusted snail mortality rates (χ2 = 14.893 and 42.284, both P values < 0.05). Treatment with 2 g/L WPPS for 72 h resulted in a 0.67% cumulative mortality rate of fish. Conclusion 25% WPPS is effective for snail control and highly safe for fish, which is feasible for use in hilly schistosomiasis-endemic regions.
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OBJECTIVE@#To evaluate the storage stability of metabolites from actinomycetes Streptomyces nigrogriseolus XD 2-7 and the mollcuscicidal activity against Oncomelania hupensis in the laboratory, and to preliminarily explore the mechanisms of the molluscicidal activity.@*METHODS@#The fermentation supernatant of S. nigrogriseolus XD 2-7 was prepared and stored at -20, 4 °C and 28 °C without light for 10 d; then, the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The fermentation supernatant was boiled in a 100 °C water bath for 30 min and recovered to room temperature, and then the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The pH values of the fermentation supernatant were adjusted to 4.0, 6.0 and 9.0 with concentrated hydrochloric acid and sodium hydroxide, and the fermentation supernatant was stilled at room temperature for 12 h, with its pH adjusted to 7.0; then, the molluscicidal effect was tested against O. hupensis following immersion for 72 h. The fermentation product of S. nigrogriseolus XD 2-7was isolated and purified four times with macroporous resin, silica gel and octadecylsilane bonded silica gel. The final products were prepared into solutions at concentrations of 10.00, 5.00, 2.50, 1.25 mg/L and 0.63 mg/L, and the molluscicidal effect of the final productswas tested against O. hupensis following immersion for 72 h, while dechlorination water served as blank controls, and 0.10 mg/L niclosamide served as positive control. The adenosine triphosphate (ATP) and adenosine diphosphate (ADP) levels were measured in in O. hupensis soft tissues using high performance liquid chromatography (HPLC) following exposure to the final purified fermentation products of S. nigrogriseolus XD 2-7.@*RESULTS@#After the fermentation supernatant of S. nigrogriseolus XD 2-7 was placed at -20, 4 °C and 28 °C without light for 10 d, immersion in the stock solution and solutions at 10- and 50-fold dilutions for 72 h resulted in a 100% (30/30) O. hupensis mortality. Following boiling at 100 °C for 30 min, immersion in the stock solution and solutions at 10- and 50-fold dilutions for 72 h resulted in a 100.00% (30/30) O. hupensis mortality. Following storage at pH values of 4.0 and 6.0 for 12 h, immersion in the fermentation supernatant of S. nigrogriseolus XD 2-7 for 72 h resulted in a 100.00% (30/30) O. hupensis mortality, and following storage at a pH value of 9.0 for 12 h, immersion in the fermentation supernatant of S. nigrogriseolus XD 2-7 for 72 h resulted in a 33.33% (10/30) O. hupensis mortality (χ2 = 30.000, P < 0.05). The minimum concentration of the final purified fermentation products of S. nigrogriseolus XD 2-7 was 1.25 mg/L for achieving a 100% (30/30) O. hupensis mortality. The ATP level was significantly lower in O. hupensis soft tissues exposed to 0.10 mg/L and 1.00 mg/L of the final purified fermentation products of S. nigrogriseolus XD 2-7 than in controls (F = 7.274, P < 0.05), while no significant difference was detected in the ADP level between the treatment group and controls (F = 2.485, P > 0.05).@*CONCLUSIONS@#The active mollcuscicidal ingredients of the S. nigrogriseolus XD 2-7 metabolites are maintained stably at -20, 4 °C and 28 °C for 10 d, and are heat and acid resistant but not alkali resistant. The metabolites from S. nigrogriseolus XD 2-7 may cause energy metabolism disorders in O. hupensis, leading to O. hupensis death.
Subject(s)
Animals , Adenosine Diphosphate/pharmacology , Adenosine Triphosphate , Molluscacides/pharmacology , Silica Gel/pharmacology , Snails , Streptomyces , WaterABSTRACT
Objective To evaluate the molluscicidal effect of 50% wettable powder of niclosamide ethanolamine salt (WPNES) against Oncomelania hupensis on the soil surface and inside the soil layer by immersion method in winter. Methods O. hupensis snails were placed on the soil surface and 2, 5 cm and 10 cm under the soil layer outdoors in winter, and then immersed in 50% WPNES at concentrations of 1 mg/L and 2 mg/L for 1, 3 d and 7 d, while dechlorinated water served as controls. Snail mortality was observed following immersion with 50% WPNES on the soil surface and inside the soil layer. Results Following immersion with 50% WPNES at concentrations of 2 mg/L and 1 mg/L outdoors in winter, the 3-day corrected snail mortality rates were 98.0% and 76.0% on the soil surface, and the 7-day corrected snail mortality rate was both 100.0%. Following immersion with 50% WPNES at concentrations of 2 mg/L and 1 mg/L outdoors in winter, the 7-day corrected snail mortality rates were 95.5% and 85.6% 2 cm below the soil layer, 66.0% and 6.4% 5 cm below the soil layer. However, the 7-day snail mortality rate swere comparable between the 50% WPNES treatment group (at 2 mg/L and 1 mg/L) and controls 10 cm below the soil layer (both P > 0.05). Conclusion Immersion of 50% WPNES at a concentration of 2 mg/L for 7 days presents a high molluscicidal efficacy against O. hupensis on the soil surface and 5 cm within the soil layers in winter.
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Objective To evaluate the effect of the water-saving irrigation project on Oncomelania hupensis snail control in hilly regions of Yixing City, Jiangsu Province. Methods A retrospective survey combined with cross-sectional investigation was employed. The implementation of the water-saving irrigation development project in Yixing City from 2005 to 2007 was retrospectively collected, and the snail status was collected in regions where the water-saving irrigation project was located and the project-affected regions from 2003 to 2018, to examine the effect of the project on snail control. In addition, a cross-sectional survey was performed to investigate the destruction of the water-saving irrigation project in 2018. Results A total of 22 water-saving irrigation projects were implemented in 5 townships in hilly regions of Yixing City from 2005 to 2007, where snail habitats were treated covering 266.97 hm2. Before the implementation of the project from 2003 to 2006, cumulative 47.87 hm2 snail habitats were detected in regions where the project was located, and no snails were found in regions where the project was located from the implementation of the project in 2006 to 2018. However, a few snails were found in the project-affected regions in 2017 and 2018. In addition, there were problems found in the later-stage maintenance and management of the project. Conclusions The water-saving irrigation projects shows a high efficiency on snail control in hilly regions of Yixing City. The later-stage maintenance of the project and monitoring of snails remain to be intensified to enhance the snail control efficiency of the water-saving irrigation project.
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Oncomelania hupensis, the only intermediate host of Schistosoma japonicum, is an indispensable part in the transmission of schistosomiasis, and snail control play a critical role in schistosomiasis prevention and control in China. This paper reviews the major molluscicides used currently and in the past and their application techniques in China. It is suggested that the research and development of molluscicides and their operational studies remain to be emphasized; notably, the novel molluscicides and new snail control techniques that meet the environmental protection requirements should be intensified. In addition, attentions should also be paid to the monitoring and evaluation of the field efficacy of molluscicides and snail control approaches, and it is necessary to evaluate the effect of molluscicides on environment and ecological security.
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Objective To compare the molluscicidal effects and cost-effectiveness of 5% niclosamide ethanolamine salt granules (NEG) and 26% suspension concentrate of metalaldehyde and niclosamide ethanolamine salt (MNSC) . Methods Two plots with high Oncomelania hupensis snail density were selected as research areas in Nanjing Chemical Industry Zone, and 5% NEG (40 g/m2) and 26% MNSC (40 g/m2) were used by the spraying method for snail control in the two plots, and their molluscicidal effects and cost-effectiveness were investigated and statistically analyzed. Results There was no significant difference between 5% NEG and 26% MNSC in the molluscicidal effects. The cost of 5% NEG was 1.25 times higher than that of 26% MN-SC per ten thousand square meters in snail control. Conclusions The cost of 5% NEG is higher than that of 26% MNSC per ten thousand square meters in snail control. Their molluscicidal effects are similar.
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Objective To compare the effectiveness of snail control between immersion of molluscicides through tide diversion and mollusciciding by spraying in marshland areas. Methods Immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion and spraying 26% suspension concentrate of metaldehyde and niclosamide alone were employed for snail control in two neighboring snail-breeding marshlands, and snails were surveyed before and after mollusciciding. The mortality of snails and the density of living snails were estimated. Results The density of living snails reduced by 72.19% and 100.00% 1 and 2 years after immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion, and 5.93% and 18.15% 1 and 2 years after spraying 26% suspension concentrate of metaldehyde and niclosamide alone. Conclusion Immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion is significantly superior to spraying 26% suspension concentrate of metaldehyde and niclosamide along for snail control, and implementation of immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion for more than 2 successive years may achieve a higher snail control efficiency.
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Objective To evaluate the effect of Oncomelania hupensis snail control of cutting the beach group in the south of Shaobo Lake. Methods The general situation of the project of cutting the beach was surveyed, and the snail distribution was surveyed and the results were compared before and after cutting the beach in the beach group. Results The area of cutting beach was 928.33 hm2, the cubic meter of earthwork was 1 717.00 m3, the area of dumping ground was 425.76 hm2, the beach surface elevation was 3.2 m after cutting the beach, and the beach surface was fallen to 1.0 m under the ordinary water level. The area with snails was 44.69 hm2 before cutting the beach in 2011 but the area with snails was 1.78 hm2 after cutting the beach in 2018. The area with remaining snails was declined by 96.02% in 2018 as compared with that in 2011, and surviving snails were distributed on the uncut beach face. Conclusion In Shaobo Lake, the O. hupensis snail breeding environment is eliminated by raising or lowering the beach, so it is an effective measure of snail control in lake regions.
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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/m2 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/m2 (all P values > 0.05). One-day field immersion with 25% PBU at doses of 1, 2 and 4 g/m3 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/m3 (all P values > 0.05), and 3-day field spraying with 25% PBU at doses of 2.0 and 4.0 g/m2 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. Conclusion 25% PBU is a novel, highly potent and environment-friendly molluscicide that is feasible in fish ponds, and the recommended dose is 1 g/m3 for field immersion and 2 g/m2 for field spraying in schistosomiasis-endemic areas of Yunnan Province.
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Objective To evaluate the effect of Oncomelania hupensis snail control of cutting the beach group in the south of Shaobo Lake. Methods The general situation of the project of cutting the beach was surveyed, and the snail distribution was surveyed and the results were compared before and after cutting the beach in the beach group. Results The area of cutting beach was 928.33 hm2, the cubic meter of earthwork was 1 717.00 m3, the area of dumping ground was 425.76 hm2, the beach surface elevation was 3.2 m after cutting the beach, and the beach surface was fallen to 1.0 m under the ordinary water level. The area with snails was 44.69 hm2 before cutting the beach in 2011 but the area with snails was 1.78 hm2 after cutting the beach in 2018. The area with remaining snails was declined by 96.02% in 2018 as compared with that in 2011, and surviving snails were distributed on the uncut beach face. Conclusion In Shaobo Lake, the O. hupensis snail breeding environment is eliminated by raising or lowering the beach, so it is an effective measure of snail control in lake regions.
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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/m2 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/m2 (all P values > 0.05). One-day field immersion with 25% PBU at doses of 1, 2 and 4 g/m3 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/m3 (all P values > 0.05), and 3-day field spraying with 25% PBU at doses of 2.0 and 4.0 g/m2 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. Conclusion 25% PBU is a novel, highly potent and environment-friendly molluscicide that is feasible in fish ponds, and the recommended dose is 1 g/m3 for field immersion and 2 g/m2 for field spraying in schistosomiasis-endemic areas of Yunnan Province.
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Objective To evaluate the effect and cost-effectiveness of three commonly used molluscicides, 4% "Luo-wei" (tea-seed distilled saponins, TDS), 50% niclosamide ethanolamine salt wettable powder (NESWP), and 26% metaldehyde and niclosamide suspension concentrate (MNSC) in large-scale field application, so as to provide the references for formulating the strategy of snail control. Methods The field test and parallel comparison were implemented. A marshland with Oncomelania hupensis snails of the Yangtze River was divided into 4 parts (10 hm2) for the research, and three of them were experimental areas while the last one was a blank control area. The experimental areas were sprayed with 4% "Luo-wei", 50% NESWP and 26% MNSC respectively for 3 times and the interval was 1 week. Seven days after each spraying the effect of snail control was investigated, and the costs of molluscicides, labor, transportation, fuel consumption and mechanical loss were recorded. The cost of each molluscicide, snail mortality, snail density, and the cost of increasing 1% of snail mortality per 100 m2 were analyzed and compared. Results After the first, second and third spraying, the corrected snail mortality rates were 67.34%, 76.55% and 84.60% respectively in the 4% "Luo-wei" group; the corrected snail mortality rates were 64.71%, 75.17% and 83.89% respectively in the 50% NESWP group; the corrected snail mortality rates were 66.55%, 76.27% and 86.67% respectively in the 26% MNSC group. There was no significant difference among the 3 groups in the snail mortality at the same spraying time (χ2 = 1.590, 0.571, 3.238, all P > 0.05) . In addition, along with the increase of the spraying times, the snail mortality of each group was increased significantly compared to that of the control group (χ2 = 79.333, 94.718, 117.020, all P < 0.01) . After the first, second and third spraying, the reduction rates of snail density were 69.82%–86.60% in the 4% "Luo-wei" group, 68.66%–86.55% in the 50% NESWP group, and 71.89%–88.87% in the 26% MNSC group respectively. The decreasing amplitude of the snail density was more than 85% in all the experimental areas after 3 rounds of spraying molluscicide. The snail control costs per 100 hm2 were 19.57, 11.97 Yuan and 10.47 Yuan in the 4% "Luo-wei" group, 50% NESWP group, and 26% MNSC group respectively. After the first, second and third spraying, the costs of increasing 1% of snail mortality per 100 m2 were 0.30, 2.08 Yuan and 2.38 Yuan in the 4% "Luo-wei" group, 0.20, 1.10 Yuan and 1.32 Yuan in the 50% NESWP group, and 0.17, 1.04 Yuan and 0.97 Yuan in the 26% MNSC group respectively, and the cost-effectiveness was the highest at the first spraying in all the three groups. Conclusions The effects of the three molluscicides for snail control are similar, but the efficacy of snail control is reduced as the spraying time increases.
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Oncomelania hupensis, the only intermediate host of Schistosoma japonicum, is an indispensable part in the transmission of schistosomiasis, and snail control play a critical role in schistosomiasis prevention and control in China. This paper reviews the major molluscicides used currently and in the past and their application techniques in China. It is suggested that the research and development of molluscicides and their operational studies remain to be emphasized; notably, the novel molluscicides and new snail control techniques that meet the environmental protection requirements should be intensified. In addition, attentions should also be paid to the monitoring and evaluation of the field efficacy of molluscicides and snail control approaches, and it is necessary to evaluate the effect of molluscicides on environment and ecological security.
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Objective To compare the effectiveness of snail control between immersion of molluscicides through tide diversion and mollusciciding by spraying in marshland areas. Methods Immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion and spraying 26% suspension concentrate of metaldehyde and niclosamide alone were employed for snail control in two neighboring snail-breeding marshlands, and snails were surveyed before and after mollusciciding. The mortality of snails and the density of living snails were estimated. Results The density of living snails reduced by 72.19% and 100.00% 1 and 2 years after immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion, and 5.93% and 18.15% 1 and 2 years after spraying 26% suspension concentrate of metaldehyde and niclosamide alone. Conclusion Immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion is significantly superior to spraying 26% suspension concentrate of metaldehyde and niclosamide along for snail control, and implementation of immersion of 26% suspension concentrate of metaldehyde and niclosamide through tide diversion for more than 2 successive years may achieve a higher snail control efficiency.
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Objective To evaluate the effect and cost-effectiveness of three commonly used molluscicides, 4% "Luo-wei" (tea-seed distilled saponins, TDS), 50% niclosamide ethanolamine salt wettable powder (NESWP), and 26% metaldehyde and niclosamide suspension concentrate (MNSC) in large-scale field application, so as to provide the references for formulating the strategy of snail control. Methods The field test and parallel comparison were implemented. A marshland with Oncomelania hupensis snails of the Yangtze River was divided into 4 parts (10 hm2) for the research, and three of them were experimental areas while the last one was a blank control area. The experimental areas were sprayed with 4% "Luo-wei", 50% NESWP and 26% MNSC respectively for 3 times and the interval was 1 week. Seven days after each spraying the effect of snail control was investigated, and the costs of molluscicides, labor, transportation, fuel consumption and mechanical loss were recorded. The cost of each molluscicide, snail mortality, snail density, and the cost of increasing 1% of snail mortality per 100 m2 were analyzed and compared. Results After the first, second and third spraying, the corrected snail mortality rates were 67.34%, 76.55% and 84.60% respectively in the 4% "Luo-wei" group; the corrected snail mortality rates were 64.71%, 75.17% and 83.89% respectively in the 50% NESWP group; the corrected snail mortality rates were 66.55%, 76.27% and 86.67% respectively in the 26% MNSC group. There was no significant difference among the 3 groups in the snail mortality at the same spraying time (χ2 = 1.590, 0.571, 3.238, all P > 0.05) . In addition, along with the increase of the spraying times, the snail mortality of each group was increased significantly compared to that of the control group (χ2 = 79.333, 94.718, 117.020, all P < 0.01) . After the first, second and third spraying, the reduction rates of snail density were 69.82%–86.60% in the 4% "Luo-wei" group, 68.66%–86.55% in the 50% NESWP group, and 71.89%–88.87% in the 26% MNSC group respectively. The decreasing amplitude of the snail density was more than 85% in all the experimental areas after 3 rounds of spraying molluscicide. The snail control costs per 100 hm2 were 19.57, 11.97 Yuan and 10.47 Yuan in the 4% "Luo-wei" group, 50% NESWP group, and 26% MNSC group respectively. After the first, second and third spraying, the costs of increasing 1% of snail mortality per 100 m2 were 0.30, 2.08 Yuan and 2.38 Yuan in the 4% "Luo-wei" group, 0.20, 1.10 Yuan and 1.32 Yuan in the 50% NESWP group, and 0.17, 1.04 Yuan and 0.97 Yuan in the 26% MNSC group respectively, and the cost-effectiveness was the highest at the first spraying in all the three groups. Conclusions The effects of the three molluscicides for snail control are similar, but the efficacy of snail control is reduced as the spraying time increases.
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Objective To compare the molluscicidal effects and cost-effectiveness of 5% niclosamide ethanolamine salt granules (NEG) and 26% suspension concentrate of metalaldehyde and niclosamide ethanolamine salt (MNSC) . Methods Two plots with high Oncomelania hupensis snail density were selected as research areas in Nanjing Chemical Industry Zone, and 5% NEG (40 g/m2) and 26% MNSC (40 g/m2) were used by the spraying method for snail control in the two plots, and their molluscicidal effects and cost-effectiveness were investigated and statistically analyzed. Results There was no significant difference between 5% NEG and 26% MNSC in the molluscicidal effects. The cost of 5% NEG was 1.25 times higher than that of 26% MN-SC per ten thousand square meters in snail control. Conclusions The cost of 5% NEG is higher than that of 26% MNSC per ten thousand square meters in snail control. Their molluscicidal effects are similar.
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To evaluate the molluscicidal effects of various water-free formulations of niclosamide ethanolamine salt against Oncomelania hupensis in the field of marshlands along the Yangtze River.The river beach with O. hupensis snails were selected as the test field in the marshland along the Yangtze River in Pukou District, Nanjing City. A molluscicidal experiment was carried out by the mechanical dusting method with the dustable powder (DP), powder-granule (PG), granule (GR) of niclosamide ethanolamine salt respectively. The snail mortality, corrected mortality, and the reduced rate of snails’ density were parallel compared among DP, PG and GR.On the 3rd day after the dusting, the snail mortality rates were 66.67%, 67.24%, and 66.87% in the DP, PG, and GR groups respectively, on the 7th day after the dusting, the snail mortality rates were 75.36%, 79.73%, and 73.97% in the DP, PG, and GR groups respectively, and there was no significant difference among the groups (χ2 = 0.006, 0.895, both P > 0.05). On the 15th day after the dusting, the snail mortality rates were 86.92%, 72.86%, and 71.43% in the DP, PG, and GR groups respectively, and there was a significant difference among the groups (χ2 = 9.709, P < 0.01). The snail mortality in the DP group was significantly higher than that in the PG, and GR groups. The curves of the snail corrected mortality and reduced rate of snails’density presented steadily rising trends in the DP group, but presented falling trends in the PG and GR groups on the 15th day after the dusting.The molluscicidal effect of DP is stable and effective in the marshland along the Yangtze River, but the drift of the powder is still not effectively controlled. It is necessary that the different dosage forms are perfected.
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Objective To evaluate the molluscicidal effect of niclosamidate against Oncomelania hupensis in laboratory and explore its mechanism by determining the enzyme activities of six important enzymes in snail soft tissues.Methods O.hupensis snails were treated with niclosamidate at the concentration of 1.25 mg/L for 24 h and the snail soft tissues were separated and pre-pared for analysis.The enzyme activities of NOS,AChE,SDH,LDH,ACP and AKP were determined by ultraviolet spectropho-tometry.The morphology of the snail soft tissue was also observed.Results Niclosamidate exhibited a potent molluscicidal ef-fect against O.hupensis at the concentration of 5.00 mg/L with a mortality of 96.67% by the immersion method in laboratory.Af-ter immersed with niclosamidate(1.25 mg/L)for 24 h,the enzyme activities of NOS,AChE,ACP and AKP were significantly decreased compared with those of the controls(all P<0.01).There were no significant changes observed in the enzyme activi-ties of SDH and LDH(both P>0.05).Conclusion Niclosamidate possesses a potent molluscicidal effect against O.hupensis and its molluscicidal mechanism is probably by affecting the transmission of neurotransmitters,interfering with the circulation, metabolism and motor functions that require NO,and hindering the digestion and absorption of nutriments,which eventually re-sult in the death of the snails.
ABSTRACT
Objective To evaluate the molluscicidal effect of suspension concentrate of niclosamide ethanolamine salt(SC-NE)against Oncomelania hupensis snails in laboratory and field. Methods The experiment of SCNE against the snails by using the immersing and spraying methods was performed in laboratory and field,with control groups of wettable powder of ni-closamide ethanolamine salt(WPN). Results In the laboratory,LC50(s) of SCNE for 24,48 h and 72 h by using the immersion method were 0.0926,0.0629 mg/L and 0.0549 mg/L,respectively. The mortality rates of snails for 24,48 h and 72 h by using the immersion method were all 100％ with the concentrations of 0.25 mg/L. The mortality rates of snails were all 100％ while spraying SCNE for 3 d in the laboratory with the concentrations of 0.25 g/m2. In Jiangling County,except 0.5 g/m3 SCNE immers-ing the snails for 24 h,the mortality rates of snails by using SCNE with the immersing method were all 100％. While the concen-tration of SCNE was 0.5 g/m3 or above,the mortality rates were all 100％after the use of it with the immersion method for 2 d in Gong'an County. In Jiangling County,the mortality rates of snails by using SCNE 0.5 g/m3 for 1 d,3 d,and 7 d with the spray-ing method were 87.5％,92.82％and 97.40％respectively. While the concentration of SCNE was 0.5 g/m3,the mortality rates were 85.94％,86.78％and 94.21％respectively after the use of it with the spraying method for 1 d,3 d,7 d in Gong'an Coun-ty,and the molluscicidal effect of SCNE(1.0 g/m2)was higher than that of WPN. Conclusion SCNE has a high molluscicidal effect in the laboratory and field,and it is a novel and simple formulation of niclosamide.