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.