Non-target toxicity of certain herbicides used in rice cultivation on mosquitoes

This study aimed to investigate the non-target toxicity (insecticidal activity) of various herbicides (bentazone+MCPA, bispyribac sodium, cyhalofop butyl, quinclorac, oxadiazon, and clomazone) used in rice cultivation on Aedes aegypti L. and Culex pipiens L. mosquitoes. Given the ecological significance of rice cultivation areas (paddy fields) and the public health importance of these mosquito species, the research sought to understand how exposure to varying herbicide doses affects mosquito survival. The research utilized a laboratory strain of Ae. aegypti and both laboratory and field strains of Cx. pipiens mosquitoes, exposing them to three distinct doses of herbicides: the recommended application rate, and doses that were two and four times higher. Toxicity tests were conducted following the World Health Organization guidelines. Adult emergence inhibition rates (%) were recorded after exposing larvae of different developmental stages; early (first-second instar) and late (third-fourth instar) to the tested herbicides. Oxadiazon consistently showed higher toxicity to mosquitoes compared to other herbicides across all tested doses, causing up to 91.67% inhibition of adult emergence. Quinclorac also demonstrated notable toxicity, but to a lesser extent and primarily in Ae. aegypti. The remaining herbicides exhibited low or no significant insecticidal effects. Notably, early-stage larvae were more susceptible across the experiments. These findings suggest that while some herbicides used in paddy fields have a minimal impact on mosquitoes, oxadiazon, in particular, poses a significant risk. Understanding these interactions can aid in developing integrated pest management strategies that consider both crop protection and mosquito control, emphasizing the need for judicious herbicide use in ecologically sensitive environments.