Impacts of changes in temperature and exposure time on the median lethal concentrations (LC50) of a combination of organophosphate and pyrethroid in the control of Culex quinquefasciatus, say (Diptera: Culicidae)

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Climate change factors such as rainfall, heat waves, rising temperatures and flooding have positively impacted insect vector population. This scenario poses considerable demand on chemical control. This study was carried out with the specific aim to examine the influence of changes in temperature and exposure time of C. quinquefasciatus to toxicities of pyrethroid (Cypermethrin), organophosphate (2, 2- dichlorovinyl dimethyl phosphate) and their mixtures. Eggs of C. quinquefasciatus were collected at the Federal University of Technology, Akure, Nigeria, in an area far from residential and cultivated zones, with a remote chance of the mosquitoes being exposed to insecticides. The eggs were allowed to hatch into larvae/pupae in the field at 27–29 °C temperature, 70–85% RH, 14:10 (L: D) photoperiod. F3 adult generation reared were transferred to the Entomology Laboratory and exposed to different concentrations of Cypermethrin and DDVP applied singly and in mixtures at varying temperatures and exposure time with mortality recorded. The median lethal concentration (LC50) values for the insecticides were higher when the insecticides were applied singly than when applied as mixtures. Therefore, mixtures of cypermethrin and DDVP have enhanced toxicity. Again, temperature changes also affect insecticide toxicity and because climate change has a characteristic temperature variability, it poses a barrier to insecticide toxicity. Hence, it is expedient to have a climate change adaptation policy in synergy with modality of chemical applications. Further study of toxico-kinetic of the insecticides in mosquito control is also recommended.