Impact of field evolved resistance on biological parameters of non-targeted Aedes aegypti populations

The yellow fever mosquito, Aedes aegypti L., known for transmitting viruses causing yellow fever, dengue, chikungunya, and Zika fever, presents a substantial risk to global human health. The development of insecticide resistance in disease vectors has become a significant problem in Ae. aegypti. Monitoring insecticide resistance is essential for resistance management in Ae. aegypti. This study involved the collection of Ae. aegypti populations from four important cotton-growing regions in southern Punjab, Pakistan, for resistance monitoring over a two-year period (2021-2022). This study also assessed the impact of insecticide resistance on biological parameters of Ae. aegypti. Moderate-to-high levels of resistance were observed against all the tested insecticides viz., chlorpyrifos, chlorfenapyr, deltamethrin, flonicamid, spirotetramat, and spinetoram. However, compared to the Lab-susceptible population, higher levels of resistance to buprofezin (59.03-84.40) and imidacloprid (68.49-100.01) were found in all populations. This high resistance can be attributed to increased use of these two insecticides in cotton fields, as compared to other insecticides. In the lab-susceptible population, higher values for the intrinsic rate of increase (r) and the net reproductive rate (R₀) i.e., 0.20 per day and 23.24 offspring/female were observed, respectively. This was also validated by population projection data where more than 2.5-fold adults (1,020,361.80 individuals) were calculated in the Lab-susceptible population as compared to the most resistant populations. Sublethal exposure to insecticides may induce physiological or biochemical changes in organisms, subsequently influencing the biological traits. Resistance monitoring provides essential guidance before launching a successful chemical-based vector management program.