Multiple insecticide resistance is challenging vectors control during a larviciding trial in the city of Yaoundé Cameroon.

Introduction:
Insecticide resistance has emerged as one of the major challenges affecting malaria vector control in Africa. The present study aimed to update data relating to insecticide susceptibility and to determine the molecular basis of resistance involved in An. gambiae populations to insecticides before and during larval control intervention in the city of Yaoundé Cameroon with larviciding as an additional tool for managing resistance and malaria transmission.
Methods: WHO susceptibility tests were conducted on adults Anopheles gambiae s.l. mosquitoes emerging from collected larvae from 32 districts surveyed. Insecticides from each class of the four classes of insecticides were evaluated using the standard susceptibility test methods during larval control intervention with larviciding between 2017 and 2019. The molecular mechanisms of mosquito resistance to these insecticides were investigated using Taqman assay. The voltage-gated sodium channel region of mosquitoes was also screened for the presence of knockdown resistance mutations (kdr west and east) by Taqman method. WHO´s susceptibility bioassays with synergist PBO were carried out to assess the implication of detoxifying enzymes in the production of resistant phenotypes. Resistance intensity and molecular identification of mosquitoes was also conducted.
Results: An. Coluzzii was predominant in Yaoundé, followed by An. gambiae. Resistance to pyrethroids, organochlorines and carbamates was persistent before and during larval control treatments with vectomax G suggesting that there was no significant variation of resistance mechanisms found in An. gambiae s.l. strains in Yaoundé. Interestingly, the demonstration of susceptibility against organophosphate compounds suggests that insecticides of this class can be used for controlling malaria transmission and elimination. Our results revealed a metabolic resistance and resistance associated with a mutation of the sodium voltage-gated channel gene at position 1014.
Conclusion: The present study showed rapid evolution of insecticide resistance in vector populations and the challenges that control programs face to maintain the continued effectiveness of insecticide-based interventions.
Keywords: Vector control; larviciding; Anopheles gambiae; insecticide resistance; resistance mechanism; Cameroon