4.3kb structural variant is associated with pyrethroid resistance
This structural variant was shown to contain two putative transposons. Several transposable elements have been identified in close proximity to metabolic resistance genes (Chen & Li, 2007), with the best characterised being the Accord insertion upstream of the CYP6G1in Drosophila melanogaster, which confers resistance to DDT has spread worldwide in this species (Catania et al., 2004). The possible role of this 4.3kb transposon-containing structural variant in pyrethroid resistance was investigated using a simple PCR assay to determine its association with the ability to survive pyrethroid insecticides exposure. A strong association was found when using field-collected samples from Gounougou and genetic crosses generated in the insectary, with most of the survivors being homozygous SV+/SV+ while heterozygous SV+/SV- and homozygous SV-/SV- were mostly dead. The association was stronger for type II pyrethroids (deltamethrin and alpha-cypermethrin) compared to type I (permethrin), indicating that this SV could be responsible for the higher resistance to type II pyrethroids observed in the Uganda and Cameroon populations (Tchouakui et al., 2021). In addition, mosquitoes with the SV+ allele were more likely to survive bed net exposure using cone assays to the standard pyrethroids-only nets (PermaNet 2.0), while PBO-containing bed nets are more effective against these mosquitoes. The results are similar to the association found with the 6.5kb SV even though the association was lower. The odds of surviving exposure to permethrin with the 6.5kb SV was 242.4 (OR) while for the 4.3kb SV it was 5.63 (OR). Further studies are needed in semi-field conditions using experimental huts as previously done for the other metabolic markers (Mugenzi et al., 2020; Weedall et al., 2019) to better understand the impact of this SV on bed net efficacy.