Background: Understanding the mechanisms used byAnophelesmosquitoes to survive insecticide exposure is key to manage existing insecticide resistance and develop more suitable insecticide-based malaria vector control interventions as well as other alternative integrated tools. To this regard, the molecular basis of permethrin, DDT and dieldrin resistance inAnopheles funestus(sensu stricto) at Akaka-Remo was investigated.Methods: Bioassays were conducted on 3–5-day-old adultAn. funestus(s.s.) mosquitoes for permethrin, DDT and dieldrin susceptibility test. The molecular mechanisms of mosquito resistance to these insecticides were investigated using microarray and reverse transcriptase PCR techniques. The voltage-gated sodium channel region of mosquitoes was also screened for the presence of knockdown resistance mutations (kdrwest and east) by sequencing method.Results: Anopheles funestus(s.s.) population was resistant to permethrin (mortality rate of 68%), DDT (mortality rate of 10%) and dieldrin (mortality rate of 8%) insecticides. Microarray and RT-PCR analyses revealed the overexpression of glutathione S-transferase genes, cytochrome P450s, esterase, trypsin and cuticle proteins in resistant mosquitoes compared to control. TheGSTe2was the most upregulated detoxification gene in permethrin-resistant (FC = 44.89), DDT-resistant (FC = 57.39) and dieldrin-resistant (FC = 41.10) mosquitoes compared to control population (FC = 22.34). The cytochrome P450 gene,CYP6P9bwas also upregulated in both permethrin- and DDT-resistant mosquitoes. The digestive enzyme, trypsin (hydrolytic processes) and the cuticle proteins (inducing cuticle thickening leading to reduced insecticides penetration) also showed high involvement in insecticide resistance, through their overexpression in resistant mosquitoes compared to control. Thekdreast and west were absent in all mosquitoes analysed, suggesting their non-involvement in the observed mosquito resistance.Conclusions: The upregulation of metabolic genes, especially theGSTe2and trypsin, as well as the cuticle proteins is driving insecticide resistance ofAn. funestus(s.s.) population. However, additional molecular analyses, including functional metabolic assays of these genes as well as screening for a possible higher cuticular hydrocarbon and lipid contents, and increased procuticle thickness in resistant mosquitoes are needed to further describe their distinct roles in mosquito resistance.

Helicoverpa armigera is an indigenous species in Africa and has been reported in the destruction of several crops in Benin. Management of H. armigera pest is mainly focused on the use of synthetic pyrethroids, which may contribute to resistance selection. This study aimed to screen the susceptibility pattern of field populations of H. armigera to deltamethrin in Benin. Relevant information on the type of pesticides used by farmers were gathered through surveys. Collected samples of Helicoverpa (F₀) were reared to F₁. F₀ were subjected to morphological speciation followed by a confirmation using restriction fragment length polymorphism coupled with a polymerase chain reaction (RFLP-PCR). F₁ (larvae) were used for insecticide susceptibility with deltamethrin alone and in the presence of the P450 inhibitor Piperonyl Butoxide (PBO). Deltamethrin and lambda-cyhalothrin were the most used pyrethroids in tomato and cotton farms respectively. All field-sampled Helicoverpa were found to be H. armigera. Susceptibility assays of H. armigera to deltamethrin revealed a high resistance pattern in cowpea (resistance factor (RF) = 2340), cotton (RF varying from 12 to 516) and tomato (RF=85) farms which is a concern for the control of this major polyphagous agricultural pest. There was a significant increase of mortality when deltamethrin insecticide was combined with piperonyl butoxide (PBO), suggesting the possible involvement of detoxification enzymes such as oxidase. This study highlights the presence of P450 induced metabolic resistance in H. armigera populations from diverse cropping systems in Benin. The recorded high levels of deltamethrin resistance in H. armigera is a concern for the control of this major agricultural pest in Benin as the country is currently embarking into economical expansion of cotton, vegetables and grain-legumes cropping systems.

The fall armyworm Spodoptera frugiperda (J.E. Smith) is a new serious destructive and widespread pest of corn which recently invaded subtropical regions worldwide. As this invasive species is spreading across the continent, it is vital to assess its susceptibility to currently used insecticides and establish the potential underlying resistance mechanism to better inform control programmes. In this study, we characterized the strains from eighteen fall armyworm populations from different countries in West Africa, established their susceptibility profiles to the main insecticides and genotyped the target site resistance alleles. The RFLP-PCR method showed that the majority of the population tested was a corn strain (72.5–100%) compared to the probable rice strain (0–27.5%). Tpi sequencing of the suspected rice strains revealed that almost all the samples analysed were from corn (> 97%). Additionally, the three insecticides tested, λ-cyhalothrin, chlorpyrifos and emamectin benzoate induced susceptible to moderate toxicity against this pest. Synergism tests performed to investigate the biochemical mechanism used by fall armyworm to breakdown λ-cyhalothrin indicated that metabolic enzymes (oxydases, esterase and the glutathion-S-transferase) play moderate roles in the resistance of λ-cyhalothrin observed in western Africa. Target mutation tests (qPCR) combined with previous synergetic tests showed that resistance to organophosphates and pyrethroids could be due to a biochemical mechanism + amino acid mutations (presence of the F290V mutation) or a biochemical mechanism (absence of the T929I mutation), respectively. The results of this study provide valuable information for supporting decisions related to sustainable fall armyworm control and applied resistance management.