[Cost-effectiveness analysis of chemical treatment with drones for Oncomelania hupensis control in marshland and lake areas].

Objective: To evaluate the molluscicidal effect and cost of spraying molluscicides with drones against Oncomelania hupensis snails in marshland and lake areas, so as to provide new insights into field snail control in China.

Methods: A marshland and lake setting measuring approximately 12 000 m² was selected in Wanzhi District, Wuhu City on June 2023 as the test field, and assigned to four groups, of 3 000 m² in each group. Environmental cleaning was not conducted in groups A or B, which were given 5% niclosamide ethanolamine salt granules sprayed with knapsack-type sprayers and drones at a dose of 40 g/m², and environmental cleaning was conducted in groups C and D, which were given 5% niclosamide ethanolamine salt granules sprayed with drones and knapsack-type sprayers at a dose of 40 g/m², respectively. O. hupensis snails were surveyed before chemical treatment and 1, 3, 5, 7, 14 days post-treatment. The uniformity of chemicals was determined on the day of treatment, and the snail mortality, corrected snail mortality and density of living snails were calculated and compared among groups. The cost of molluscicides, labor fees of environmental cleaning and chemical treatment and cost of equipment were calculated, and the cost for a 1% reduction in the mean density of living snails was calculated 14 days post-treatment.

Results: The mean densities of living snails and mortality rates of snails were 1.82 to 2.85 snails/0.1 m² and 1.41% to 2.94% in groups A, B, C and D before chemical treatment, and the mortality and corrected mortality of snails were 55.75%, 49.32%, 85.94% and 87.50%, and 55.00%, 48.47%, 85.70% and 87.29% in groups A, B, C and D 14 days post-treatment. There was a significant difference in the mortality of snails among the four groups 14 days post-treatment (χ² = 38.735, P < 0.005), and there was a higher snail mortality in Group D than in Group A (χ² = 16.876, P < 0.005), and higher in Group C than in Group B (χ² = 20.508, P < 0.005). The density of living snails reduced by 55.00%, 43.94%, 90.43% and 87.14% 14 days post-treatment relative to pre-treatment in groups A, B, C and D, respectively. The test for uniformity of chemicals showed that the mean dose of molluscicides were 57.34, 55.21, 40.19 g/m² and 32.37 g/m² in groups A, B, C and D, respectively, and the minimal standard deviation (7.07) and coefficient of variation (0.18) of mean doses were seen in Group C. The costs for chemical treatment were 0.33 Yuan in groups A and B and 1.53 Yuan in groups C and D, respectively. The costs for a 1% reduction in the mean density of living snails were 17.82, 22.47, 50.73 Yuan and 52.56 Yuan in groups A, B, C, and D 14 days post-treatment, respectively.

Conclusions: The molluscicidal effect and cost of spraying 5% niclosamide ethanolamine salt granules with drones are comparable to manual spraying, and chemical treatment with drones are high in uniformity of molluscicides, time- and labor-saving, and feasible for applications in complex environments, which deserves widespread applications in the field of snail control.