Status of Insecticide Resistance and Its Mechanisms in and Populations from Forest Settings in South Cameroon.

A key factor affecting malaria vector control efforts in Cameroon is the rapid expansion of insecticide resistance in s.l ) populations; however, mechanisms involved in insecticide resistance in forest mosquito populations are still not well documented yet. The present study was conducted to screen molecular mechanisms conferring insecticide resistance in s.l. populations from the South Cameroon forest region. WHO bioassays were conducted with F0 females aged three to four days from forest (Sangmelima, Nyabessan, and Mbandjock) and urban sites (Yaoundé (Bastos and Nkolondom)), against pyrethroids (permethrin 0.75% and deltamethrin 0.05%) and carbamates (bendiocarb 0.1%). Members of the s.l. species complex were identified using molecular diagnostic tools. TaqMan assays were used to screen for target site mutations. The expression profiles of eight genes implicated in insecticide resistance were assessed using RT-qPCR. Cuticle hydrocarbon lipids were measured to assess their potential implication in insecticide resistance. Both and were detected. was highly prevalent in Sangmelima, Nyabessan, Mbandjock, and Nkolondom. was the only species found in the Yaoundé city center (Bastos). Low mortality rate to both pyrethroids and bendiocarb was recorded in all sites. High frequency of L1014F allele (75.32-95.82%) and low frequencies of L1014S (1.71-23.05%) and N1575Y (5.28-12.87%) were recorded. The G119S mutation (14.22-35.5%) was detected for the first time in populations from Cameroon. This mutation was rather absent from populations. The detoxification genes , , , , as well as which catalyzes epicuticular hydrocarbon biosynthesis, were found to be overexpressed in at least one population. The total cuticular hydrocarvbon content, a proxy of cuticular resistance, did not show a pattern associated with pyrethroid resistance in these populations. The rapid emergence of multiple resistance mechanisms in s.l. population from the South Cameroon forest region is of big concern and could deeply affect the sustainability of insecticide-based interventions strategies in this region.