Behavioural response of mosquito vectors Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus to synthetic pyrethroid and organophosphorus-based slow-release insecticidal paint

Abstract Background The direct toxicological impact of insecticides on vector mosquitoes has been well emphasized; however, behavioural responses such as excito-repellency and physical avoidance as a result of insecticide exposure have not been much studied. We have demonstrated the excito-repellency and behavioural avoidance in certain vector mosquito species on exposure to a slow-release insecticidal paint (SRIP) formulation in addition to direct toxicity. Methods A SRIP formulation developed by the Defence Research and Development Establishment, Gwalior, contains chlorpyriphos, deltamethrin and pyriproxyfen as active insecticides.Anopheles stephensi, Culex quinquefasciatusandAedes aegyptimosquitoes were used to study the excito-repellency response of the formulation. The experiments were performed in a specially designed dual-choice exposure and escape chamber made of transparent polymethyl methacrylate. For the experiments, the SRIP formulation was applied undiluted at a rate of 8 m2per kg on 15 cm2metallic surfaces. Mosquitoes were introduced into the exposure chamber, and observations of the movement of mosquitoes into the escape chamber through the exit portal were taken at 1-min intervals for up to 30 min. Results The evaluated formulation displayed strong excito-repellency against all three tested vector mosquito species. Results showed that the ET50(escape time 50%) forAe. aegypti,An. stephensiandCx. quinquefasciatuswas 20.9 min, 14.5 min and 17.9 min for contact exposure (CE) respectively. Altogether in CE, the escape rates were stronger inAn. stephensimosquitoes at different time intervals compared toAe. aegyptiandCx. quinquefasciatusmosquitoes. The probit analysis revealed that the determined ET did not deviate from linearity for both non-contact exposure (NCE) and placebo exposure (PE) (χ2 ≤ 7.9;p = 1.0) forAe. aegyptimosquitoes and for NCE (χ2 = 8.3;p = 1.0) and PE (χ2 = 1.7;p = 1.0) treatments inCx. quinquefasciatus. Mortality (24 h) was found to be statistically higher (F = 6.4;p = 0.02) inAn. stephensifor CE but did not vary for NCE (p ≥ 0.3) and PE (p = 0.6) treatments among the tested mosquito species. Survival probability response suggested that all the three tested species displayed similar survival responses for similar exposures (χ2 ≤ 2.3;p ≥ 0.1). Conclusion The study demonstrates the toxicity and strong behavioural avoidance in known vector mosquito species on exposure to an insecticide-based paint formulation. The combination of insecticides in the present formulation will broaden the overall impact spectrum for protecting users from mosquito bites. The efficacy data generated in the study provide crucial information on the effectiveness of the tested formulation and could be useful in reducing the transmission intensity and disease risk in endemic countries. Graphical Abstract