Insecticide resistance status predetermines behavioural responses and oviposition fitness in Anopheles coluzzii

Behavioural resistance is one of the major public health challenges facing planned vector control strategies involving insecticides. Understanding the behaviour of mosquitoes holistically when exposed to insecticides could be key to adding up to the fight against resistance. This study evaluated the behavioural responses and oviposition fitness of male and female Anopheles coluzzii exposed to selected pyrethroids, including lambda-cyhalothrin (0.05%), permethrin (0.75%), and DDT (4%). Male and female mosquitoes, aged three to five days, were exposed in eight replicates to selected insecticides for 60 minutes. Susceptibility to insecticide exposure was assessed in a total of 2,000 mosquitoes (eight replicates of 25 per sex per insecticide, across three insecticides), while behavioural assays used resistant and unexposed cohorts of 15 mosquitoes per replicate, in triplicate, for three insecticides (lambda-cyhalothrin, permethrin, and DDT). Resistant male and female mosquitoes were separated in holding buckets, tagged, sugar-fed, and kept to acclimatize for 1 hour before further exposure for the behavioural study. Square-shaped containers connected by a pipe into an H-shape were used for the experiment. Resistant mosquitoes (n = 15) were exposed to different chambers with insecticide-treated paper (WITP) and without insecticide-treated paper (WOITP) in triplicate. A similar experiment was done for unexposed mosquitoes. The flight efficiency, resting efficiency, repellency, landing, and biting efficiency of mosquitoes were recorded. Sex crossing between exposed and unexposed mosquitoes was done, and oviposition fitness was assessed. Flight efficiency of resistant mosquitoes WITP increased (mean 3.00-30.5) whereas WOITP decreased (mean 2.00-0.50) significantly (p < 0.0001). Resting efficacy WITP decreased (mean 12.50-0.00) while WOITP increased (mean 11.50-13.50) significantly (p < 0.0001). Repellency WITP decreased (mean 14.00-0.00), while WOITP did not follow a regular pattern. Likewise, landing and biting did not follow a regular pattern. Unexposed female mosquitoes had the highest blood meal (mean of 11.5). The highest ovipositioning was recorded in unexposed males and females (mean of 0.33), but no ovipositioning was recorded in other crosses (mean of 0.00). Insecticide exposure induces both behavioural avoidance and reproductive impairment in resistant Anopheles coluzzii, emphasizing the importance of incorporating behavioural endpoints into resistance monitoring programs.