[Molluscicidal effect and costs of spraying pyriclobenzuron with drones against Pomacea canaliculata].

Objective: To evaluate the molluscicidal effects and costs of spraying 20% suspension concentrate of pyricloben-zuron sulphate (SCPS) with drones against Pomacea canaliculata in paddy environments, so as to provide insights into the extensive applications of pyriclobenzuron against P. canaliculata.

Methods: On July 2022, a paddy field was selected from Nanchang City, Jiangxi Province as the study area, and 72 independent rectangular plots measuring 2 m × 1 m were allocated in the study area, with 1 m interval between each plot, and 20 P. canaliculata snails gently placed in each plot. The activity of 25% wettable powder of pyriclobenzuron sulphate (WPPS) by manual spraying at doses of 0.50, 1.00, 2.00 g/m² and 4.00 g/m² against P. canaliculata was tested in 54 plots, and manual spraying of 50% wettable powder of niclosamide ethanolamine salt (WPNES) at a dose of 0.10 g/m² served as a chemical control, while manual spraying of the same volume of clean water served as a blank control, with 9 plots in each group. The activity of SCPS against P. canaliculata was tested in the remaining 18 plots. Based on the molluscicidal tests of WPPS, the molluscicidal effect of SCPS by manual spraying at doses of 0.20, 0.30, 0.40 g/m² and 0.50 g/m² against P. canaliculata was evaluated, and manual spraying of WPNES at a dose of 0.10 g/m² served as a chemical control, while manual spraying of the same volume of clean water served as a blank control, with three plots in each group. On July 2023, 14 paddy fields with a mean living P. canaliculata density of > 5 snails/m² were selected from Yujiang District, Yingtan City, Jiangxi Province for molluscicidal tests. Based on the molluscicidal effect of pyriclobenzuron against P. canaliculata in plots, the molluscicidal effects of WPPS by manual spraying at doses of 0.25, 0.50 g/m² and 1.00 g/m² and manual applications of WPPS at dose of 0.25, 0.50, 1.00 g/m² and 2.00 g/m² mixed with soil were tested, and manual spraying of 0.10 g/m² WPNES served as a chemical control group, while manual spraying of the same volume of clean water served as a blank control, with one paddy field in each group. Based on the effect of pyriclobenzuron against P. canaliculata in plots, the activity of SCPS sprayed with drones at doses of 0.25 g/m² and 0.50 g/m² mixed in water at 2 kg/667 m² and 4 kg/667 m² was tested against P. canaliculata, and spraying of the same volume of clean water with drones served as a blank control. All P. canaliculata snails were captured 3 days and 7 days following chemical treatment in plots and paddy fields and identified for survival, and the mortality and corrected mortality of P. canaliculata snails were estimated. In addition, the areas of chemical treatment, amount of molluscicide use and labor costs of chemical treatment were estimated in molluscicidal tests in paddy fields, and the costs of chemical treatment for an area covering 667 m² by drones and manual applications were calculated.

Results: The mortality of P. canaliculata snails was all 100% in plots 3 days and 7 days following spraying WPPS at doses of 0.50, 1.00, 2.00 g/m² and 4.00 g/m², and the mortality rates of P. canaliculata snails were 66.67% to 100.00% 3 days post-treatment with SCPS at various doses (χ² = 277.897, P < 0.05) and 76.67% to 100.00% 7 days post-treatment (χ² = 274.206, P < 0.05). The mortality rates of P. canaliculata snails were 98.19% to 100.00% 3 days post-treatment with WPPS at various doses in paddy fields. There was a significant difference in the mortality of P. canaliculata snails among WPPS treatment groups and controls (χ² = 270.778, P < 0.05), and there were no significant differences between WPPS treatment groups and the chemical control group (all P values > 0.05), while there were significant differences in the mortality of P. canaliculata snails between WPPS treatment groups and the blank control group (all P values < 0.05). The mortality rates of P. canaliculata snails were 89.83% to 95.31% 3 days post-treatment with SCPS at various doses sprayed with drones, and there was a significant difference in the mortality of P. canaliculata snails among SCPS treatment groups and the blank control group (χ² = 1 132.892, P < 0.05). There were no significant differences in the mortality of P. canaliculata snails among SCPS treatment groups or water mixture groups (all P values > 0.05), and there were significant differences in the mortality of P. canaliculata snails between SCPS treatment groups and the blank control group (all P values < 0.05). The mortality rates of P. canaliculata snails were 94.62% to 100.00% 7 days post-treatment with SCPS at various doses sprayed with drones, and there was a significant difference in the mortality of P. canaliculata snails among SCPS treatment groups and the blank control group (χ² = 1 266.932, P < 0.05), with the highest mortality found following spraying 0.50 g/m² SCPS mixed in 2 kg/667 m² water with drones (P < 0.05). The costs of P. canaliculata snail control by drones and manually were 35.85 Yuan/667 m² and 43.33 Yuan/667 m²; however, the snail control efficiency was 6.67 times higher by drones than by manual applications.

Conclusions: SCPS sprayed with drones is highly active against P. canaliculata snails in paddy fields. SCPS sprayed with drones is highly efficient and low in cost for P. canaliculata snail control in paddy fields, beaches and river courses.