In Benin, synthetic insecticides are the main pest control option used by farmers to protect and enhance their production. However, failures to control the target pests are often observed after application and may be related to agricultural practices or insecticide quality. The present work was designed to assess a rapid, simple, and reliable analytical method for detecting and quantifying the most commonly used insecticides (λ-cyhalothrin and acetamiprid) in Benin. The analytical standard technical grade separation was performed by gradient reversed-phase high-performance liquid chromatography on a C₁₈ stationary-phase column. The mobile phase consisted of a mixture of acetonitrile/water using a gradient flow. The flow rates were 1 and 1.4 mL·min⁻¹ for λ-cyhalothrin and acetamiprid, respectively. The analysis times were 15 and 20 min, with retention times of 2.35 and 7.94 min for λ-cyhalothrin and acetamiprid, respectively. Results reveal that most of the surveyed farmers were not educated (70% < Primary School Certificate) and were men (95%). Of the main insecticides applied by farmers, λ-cyhalothrin and acetamiprid were found to be the most technical-grade ones. Furthermore, the analysis of insecticides showed that the concentrations obtained in our study often differed from the ones mentioned on insecticide labels. The proposed method is useful for quantifying insecticides in various technical and commercial formulations with little interference from additives.

Agricultural pesticides may play a crucial role in the selection of resistance in field populations of mosquito vectors. This study aimed to determine the susceptibility level of An. gambiae s.l. to pyrethroids and neonicotinoids in vegetable farms in northern Benin, in West Africa, and the underlying insecticide resistance mechanisms. A survey on agricultural practices was carried out on 85 market gardeners chosen randomly in Malanville and Parakou. Anopheles gambiae s.l. larvae were collected, reared to adult stages, and identified to species level. Susceptibility was tested with impregnated papers (WHO bioassays) or CDC bottles according to the insecticides. Synergists (PBO, DEM, and DEF) were used to screen resistance mechanisms. Allelic frequencies of the kdr (L1014F), kdr (L1014S), N1575Y, and ace-1R G119S mutations were determined in mosquitoes using Taqman PCR. Fertilizers and pesticides were the agrochemicals most used with a rate of 97.78% and 100%, respectively, in Malanville and Parakou. Anopheles coluzzii was the predominant species in Malanville, while An. gambiae was the only species found in Parakou. Bioassays revealed a high resistance of An. gambiae s.l. to pyrethroids and DDT, while a susceptibility to bendiocarb, pyrimiphos-methyl, malathion, and clothianidin was recorded. Resistance to acetamiprid was suspected in mosquitoes from both localities. A lower resistance level was observed when mosquitoes were pre-treated with synergists, then exposed to insecticides. The kdr L1014F mutation was observed in both locations at moderate frequencies (0.50 in Malanville and 0.55 in Parakou). The allelic frequencies of N1575Y and G119S were low in both study sites. This study confirmed the resistance of An. gambiae s.l. to insecticides used in agriculture and public health. It reveals a susceptibility of vectors to bendiocarb, pyrimiphos-methyl, malathion, and clothianidin, thus indicating that these insecticides can be used as an alternative in Benin to control malaria vectors.

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, among the three insecticides tested, λ-cyhalothrin and chlorpyrifos induced the lowest toxicity against this pest, while emamectin benzoate exhibited moderate toxicity. 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 major 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.