Evaluating β-isocostic acid’s toxicity to wetland predators Diplonychus indicus and Gambusia affinis for sustainable mosquito control
摘要
The increasing reliance on synthetic insecticides for mosquito control has led to environmental concerns and insecticide resistance among mosquito populations. In response, plant-based bioactive compounds are gaining attention as eco-friendly alternatives with minimal impact on non-target organisms. This study investigates the toxicological effects of β-isocostic acid, a compound derived from Sphaeranthus indicus leaves, on two non-target mosquito predators, Gambusia affinis (mosquitofish) and Diplonychus indicus (water bug). Both species share habitats with mosquito vectors Aedes aegypti and Culex quinquefasciatus, emphasizing the importance of evaluating impacts on these natural regulators. These predators are key components of wetland ecosystems, where they regulate populations of wetland-dwelling mosquitoes like Cx. quinquefasciatus, common in marshes and ponds. Predators were collected from the Fishery Research Institute Pond, Chetpet, Chennai, a managed aquatic habitat with wetland characteristics, and acclimatized before exposure to concentrations of the compound (0.5, 1.0, 1.5, and 2.0 ppm). Mortality and behavioural changes were assessed over 24 h, with extended observation for 15 days post-treatment. Results indicated LC50 values of 2.66 ppm and 2.78 ppm for D. indicus and G. affinis, respectively, with qualitative observations suggesting minimal impact on survival or swimming behaviour, indicating low toxicity at tested concentrations. The Predator Safety Factor (PSF) values for both species support the compound’s suitability in integrated pest management (IPM) programs. Overall, β-isocostic acid shows promise as a low-risk larvicide that preserves aquatic biodiversity and can contribute to sustainable mosquito control in wetland ecosystems.