Insecticide resistance modifies behavioural response of Anopheles gambiae sensu stricto to insecticide-treated nets

Abstract Background: Behavioural responses of mosquito vectors to insecticide-treated materials are critical aspects of disease control and for insecticide resistance management. Physiological resistance to insecticides may change mosquitoes’ behavioural response to insecticide-treated materials such as bed nets. Methods: Using free-flying bioassay conducted in cubic-shape cages with different net materials on different sides of the cage, we examined the behavioural responses of insecticide-resistant (Bungoma strain) and susceptible (Kisumu strain) Anopheles gambiae sensu stricto mosquitoes to different types of long-lasting insecticidal nets (LLINs) including the piperonyl butoxide treated (PBO) LLIN using untreated nets as control. We conducted video tracking of mosquito flying paths and analysed landing attempts, resting preference and resting duration on treated and untreated netting materials. Kisumu susceptible strain (An. gambiae s.s) was used as a control.Results: We found that for both field and susceptible strain mosquitoes PBO nets caused significantly higher mortalities. Direct observation found that the resistant strain mosquitoes showed significant inactive overall compared to susceptible mosquitoes regardless of net material. Direct observations found that resistant mosquitoes showed 5-10 fold higher proportion of resting on the non-treated nets (10~20% resting rate) compared to treated nets (<2% resting rate), whereas, susceptible mosquitoes resting equally on treated and untreated nets (~5%). Based on video tracking results, mosquito landing attempts on the nets were low in the control cages and similar for both strains of mosquitoes, landing attempts of the susceptible mosquitoes increased 7-10 fold against the insecticide treated nets, whereas landing attempts of the resistant mosquitoes increased only about 3-fold against PBO-treated nets but not regular LLIN. The average resting duration on the nets was 100-120 seconds in the control cage regardless of mosquito strains while resting duration reduced to 5-15 s against regular nets and 5-30 s against PBO nets. Overall, compared to the susceptible mosquitoes, the resistant mosquitoes had a significantly lower number of landing attempts and resting on the insecticide-treated nets. Conclusion: Based on the overall behaviour analysis, the evidence suggested that the resistant An. gambiae s.s. mosquitoes were inactive against insecticide-treated nets. The results from this study explain why mortality in resistant mosquitoes was low in the presence of LLINs – they did not contact often and did not rest often on the treated nets.