Multiple Pyrethroid Resistance in Urban Male and Female An. gambiae s.l Populations in Ilorin Nigeria: Implications for Swarm Spraying and Toxic Sugar Bait Malaria Vector Control

Abstract

Background: Male mosquito control through swarm spraying and Attractive Toxic Sugar Baits (ATSB) have been identified as potential strategies to complement the regular but insufficient female mosquito-based insecticide-treated net (ITN) approach. However, the effectiveness of these control strategies relies on under-standing the insecticide susceptibility status of the targeted male and female mosquito populations. Therefore, this study aimed to assess the insecticide susceptibility status of male and female An. gambiae s.l. Popu-lations in urban Ilorin, Nigeria. Methods: Using WHO kits and protocol, adult male and female mosquitoes reared from the same larval col-lections from different sites were exposed separately to permethrin, deltamethrin, and alphacypermethrin insecticides. Joint insecticide susceptibility tests, involving exposures of equal numbers of male and female mosquitoes to each insecticide, were also conducted in anticipation of joint insecticide exposure on the field. Exposed mosquitoes were identified to species level. Results: Higher kdt50s (52.5-641.3mins) and lower mortalities (permethrin 39-62%, deltamethrin 57-68%, alphacypermethrin 44-60%), indicating higher levels of resistance, were observed for the females compared to the male (22.1-42.2 mins, 60-94%) mosquitoes. The percentage mortalities of males (71-94%) were sig-nificantly (P ≤ 0.043) higher than those of the jointly exposed females (39-62%). However, separately ex-posed male mosquito mortalities (60-81%) were not significantly (P ≥ 0.067) higher than the females (55-68%). All the male mosquito populations were resistant to permethrin (75-94% mortality), deltamethrin (60-82%), and alphacypermethrin (74-86%) insecticides after joint and separate exposures. Resistant male and female mosquitoes were identified predominantly as An. arabiensis (74-84%). Conclusion: Multiple pyrethroid insecticide resistance detected in the male and female mosquito populations indicates the potential ineffectiveness of pyrethroid-based swarm spraying, pyrethroid ATSB and ITNs in the study location