Genetic Diversity and Population Structure of the Invasive Oriental Fruit Fly, Bactrocera dorsalis (Diptera: Tephritidae) in Burkina Faso.

Bactrocera dorsalis Hendel is a highly invasive horticultural pest that is of major economic importance worldwide. In Burkina Faso, it is one of the main insect pests that affects the production and exportation of mangos. Understanding the biology and the genetic dynamics of this insect pest provides crucial information for the development of effective control measures. The aim of this study was to understand the distribution, diversity, and genetic structure of B. dorsalis in Burkina Faso. Male flies were collected transversally in Burkina Faso and analyzed by PCR using 10 microsatellite markers. The results showed an abundance of B. dorsalis varying from 87 to 2986 flies per trap per day at the different sampling sites. The genetic diversity was high at all sites, with an average Shannon's Information Index (I) of 0.72 per site. The gene flow was high between study populations and ranged from 10.62 to 27.53 migrants. Bayesian admixture analysis showed no evidence of structure, while Discriminant Analysis of Principal Components identified three weakly separated clusters in the population of B. dorsalis in Burkina Faso. The results of this study could be used to optimize the effectiveness of current control interventions and to guide the implementation of new, innovative, and sustainable strategies.

Mosquito (Diptera: Culicidae) populations in contrasting areas of the western regions of Burkina Faso: species diversity, abundance and their implications for pathogen transmission.

BACKGROUND: Mosquitoes (Diptera: Culicidae) can have a significant negative impact on human health. The urbanization of natural environments and their conversion for agricultural use, as well as human population growth, may affect mosquito populations and increase the risk of emerging or re-emerging mosquito-borne diseases. We report on the variety and number of adult mosquitoes found in four environments with varying degrees of human impact (rural, urban, rice fields, and forest) located in a savannah zone of West Africa. METHODS: Mosquitoes were collected from two regions (Hauts-Bassins and Sud-Ouest) of Burkina Faso during five periods between August 2019 and June 2021. Sampling sites were grouped according to environment. Mosquitoes were collected using BG-Sentinel traps and double net traps, and Prokopack Aspirators. Statistical analyses were performed using R software version 4.1.2. Logistic regression, using generalised mixed linear models, was used to test the effect of environment on mosquito abundance and diversity. Alpha diversity analysis was also performed, using the vegan package. RESULTS: A total of 10,625 adult mosquitoes were collected, belonging to 33 species and five genera: Culex, Aedes, Anopheles, Mansonia, and Ficalbia. The most dominant species were Culex quinquefasciatus, Anopheles gambiae sensu lato and Aedes aegypti. Alpha diversity was similar in the two regions. Habitat had a significant effect on mosquito species richness, the Shannon index and the Simpson index. The rural environment had the highest species richness (n = 28) followed by the forest environment (n = 24). The highest number of mosquitoes (4977/10,625) was collected in the urban environment. CONCLUSIONS: The species composition of the mosquito populations depended on the type of environment, with fewer species in environments with a high human impact such as urban areas and rice fields. Due to the diversity and abundance of the mosquito vectors, the human populations of all of the environments examined are considered to be at potential risk of mosquito-borne diseases.

Analysis of the Genetic Variation of the Fruitless Gene within the Anopheles gambiae (Diptera: Culicidae) Complex Populations in Africa.

Targeting genes involved in sexual determinism, for vector or pest control purposes, requires a better understanding of their polymorphism in natural populations in order to ensure a rapid spread of the construct. By using genomic data from An. gambiae s.l., we analyzed the genetic variation and the conservation score of the fru gene in 18 natural populations across Africa. A total of 34,339 SNPs were identified, including 3.11% non-synonymous segregating sites. Overall, the nucleotide diversity was low, and the Tajima's D neutrality test was negative, indicating an excess of low frequency SNPs in the fru gene. The allelic frequencies of the non-synonymous SNPs were low (freq < 0.26), except for two SNPs identified at high frequencies (freq > 0.8) in the zinc-finger A and B protein domains. The conservation score was variable throughout the fru gene, with maximum values in the exonic regions compared to the intronic regions. These results showed a low genetic variation overall in the exonic regions, especially the male sex-specific exon and the BTB-exon 1 of the fru gene. These findings will facilitate the development of an effective gene drive construct targeting the fru gene that can rapidly spread without encountering resistance in wild populations.

High-resolution species assignment of Anopheles mosquitoes using k-mer distances on targeted sequences.

The ANOSPP amplicon panel is a genus-wide targeted sequencing panel to facilitate large-scale monitoring of Anopheles species diversity. Combining information from the 62 nuclear amplicons present in the ANOSPP panel allows for a more senstive and specific species assignment than single gene (e.g. COI) barcoding, which is desirable in the light of permeable species boundaries. Here, we present NNoVAE, a method using Nearest Neighbours (NN) and Variational Autoencoders (VAE), which we apply to k-mers resulting from the ANOSPP amplicon sequences in order to hierarchically assign species identity. The NN step assigns a sample to a species-group by comparing the k-mers arising from each haplotype's amplicon sequence to a reference database. The VAE step is required to distinguish between closely related species, and also has sufficient resolution to reveal population structure within species. In tests on independent samples with over 80% amplicon coverage, NNoVAE correctly classifies to species level 98% of samples within the An. gambiae complex and 89% of samples outside the complex. We apply NNoVAE to over two thousand new samples from Burkina Faso and Gabon, identifying unexpected species in Gabon. NNoVAE presents an approach that may be of value to other targeted sequencing panels, and is a method that will be used to survey Anopheles species diversity and Plasmodium transmission patterns through space and time on a large scale, with plans to analyse half a million mosquitoes in the next five years.

Insecticide resistance status of malaria vectors Anopheles gambiae (s.l.) of southwest Burkina Faso and residual efficacy of indoor residual spraying with microencapsulated pirimiphos-methyl insecticide.

BACKGROUND: The rapid spread of insecticide resistance in malaria vectors and the rebound in malaria cases observed recently in some endemic areas underscore the urgent need to evaluate and deploy new effective control interventions. A randomized control trial (RCT) was conducted with the aim to investigate the benefit of deploying complementary strategies, including indoor residual spraying (IRS) with pirimiphos-methyl in addition to long-lasting insecticidal nets (LLINs) in Diébougou, southwest Burkina Faso. METHODS: We measured the susceptibility of the Anopheles gambiae (s.l.) population from Diébougou to conventional insecticides. We further monitored the efficacy and residual activity of pirimiphos-methyl on both cement and mud walls using a laboratory susceptible strain (Kisumu) and the local An. gambiae (s.l.) population. RESULTS: An. gambiae (s.l.) from Diébougou was resistant to DDT, pyrethroids (deltamethrin, permethrin and alphacypermethrin) and bendiocarb but showed susceptibility to organophosphates (pirimiphos-methyl and chlorpyrimiphos-methyl). A mixed-effect generalized linear model predicted that pirimiphos-methyl applied on cement or mud walls was effective for 210 days against the laboratory susceptible strain and 247 days against the local population. The residual efficacy of pirimiphos-methyl against the local population on walls made of mud was similar to that of cement (OR = 0.792, [0.55-1.12], Tukey's test p-value = 0.19). CONCLUSIONS: If data on malaria transmission and malaria cases (as measured trough the RCT) are consistent with data on residual activity of pirimiphos-methyl regardless of the type of wall, one round of IRS with pirimiphos-methyl would have the potential to control malaria in a context of multi-resistant An. gambiae (s.l.) for at least 7 months.

Insecticide resistance profiles in malaria vector populations from Sud-Kivu in the Democratic Republic of the Congo.

BACKGROUND: Insecticide resistance has become a widespread problem causing a decline in the effectiveness of vector control tools in sub-Saharan Africa. In this situation, ongoing monitoring of vector susceptibility to insecticides is encouraged by the WHO to guide national malaria control programmes. Our study was conducted from April to November 2018 in Tchonka (Sud-Kivu, Democratic Republic of the Congo) and reported primary data on the resistance status of Anopheles funestus and Anopheles gambiae. METHODS: Insecticide susceptibility bioassays were performed on wild populations of A. funestus and A. gambiae using WHO insecticide-impregnated papers at discriminating concentration. In addition, PCR was performed to identify mosquito species and to detect kdr and ace-1R mutations involved in insecticide resistance. RESULTS: Bioassay results show resistance to all tested insecticides except pirimiphos-methyl, propoxur, fenitrothion and malathion with a mortality rate ranging from 95.48 to 99.86%. The addition of piperonyl butoxide (PBO) increased the susceptibility of vectors to deltamethrin and alpha-cypermethrin by exhibiting a mortality ranging from 91.50 to 95.86%. The kdr mutation was detected at high frequencies (approximately 0.98) within A. gambiae while ace-1R was not detected. CONCLUSIONS: This study provides useful data on the insecticide resistance profiles of malaria vector populations to better manage vector control. Our results highlight that, despite the high level of resistance, organophosphorus compounds and pyrethroids + PBO remain effective against the vectors.

Monitoring Insecticide Susceptibility in Aedes Aegypti Populations from the Two Biggest Cities, Ouagadougou and Bobo-Dioulasso, in Burkina Faso: Implication of Metabolic Resistance.

In West Africa, Aedes aegypti remains the major vector of dengue virus. Since 2013, dengue fever has been reemerging in Burkina Faso with annual outbreaks, thus becoming a major public health problem. Its control relies on vector control, which is unfortunately facing the problem of insecticide resistance. At the time of this study, although data on phenotypic resistance were available, information related to the metabolic resistance in Aedes populations from Burkina Faso remained very scarce. Here, we assessed the phenotypic and the metabolic resistance of Ae. aegypti populations sampled from the two main urban areas (Ouagadougou and Bobo-Dioulasso) of Burkina Faso. Insecticide susceptibility bioassays to chlorpyriphos-methyl 0.4%, bendiocarb 0.1% and deltamethrin 0.05% were performed on natural populations of Ae. aegypti using the WHO protocol. The activity of enzymes involved in the rapid detoxification of insecticides, especially non-specific esterases, oxidases (cytochrome P450) and glutathione-S-transferases, was measured on individual mosquitos. The mortality rates for deltamethrin 0.05% were low and ranged from 20.72% to 89.62% in the Bobo-Dioulasso and Ouagadougou sites, respectively. When bendiocarb 0.1% was tested, the mortality rates ranged from 7.73% to 71.23%. Interestingly, in the two urban areas, mosquitoes were found to be fully susceptible to chlorpyriphos-methyl 0.4%. Elevated activity of non-specific esterases and glutathione-S-transferases was reported, suggesting multiple resistance mechanisms involved in Ae. aegypti populations from Bobo-Dioulasso and Ouagadougou (including cytochrome P450). This update to the insecticide resistance status within Ae. aegypti populations in the two biggest cities is important to better plan dengue vectors control in the country and provides valuable information for improving vector control strategies in Burkina Faso, West Africa.

Insecticide resistance mechanisms in Anopheles gambiae complex populations from Burkina Faso, West Africa.

Vector control constitutes a fundamental approach in reducing vector density and the efficient option to break malaria transmission in Africa. Malaria vectors developed resistance to almost all classes of insecticides recommended by WHO for vector control in most places of African countries and may compromise the vector control strategies. This study updated the resistance status of Anopheles gambiae complex populations to insecticides recommended for vector control in the western part of Burkina Faso. Insecticide susceptibility bioassays were performed on seven natural populations of An. gambiae complex from western Burkina Faso in the 2016 rainy season using the WHO protocol. Biochemical assays were carried out according to the WHO protocol on the same populations to estimate detoxifying enzymes activities including non-specific esterases (NSEs), oxidases (cytochrome P450) and Glutathione-S-Transferases (GSTs). Polymerase Chain Reactions (PCRs) were performed for the identification of the An. gambiae complex species as well as the detection of kdr-west and ace-1 mutations. Susceptibility bioassays showed that An. gambiae complex was multi-resistant to pyrethroids, DDT and carbamates in almost all areas. The mortality rates ranged from 10 to 38%, 2.67 to 59.57% and 64.38 to 98.02% for Deltamethrin, DDT and Bendiocarb respectively. A full susceptibility (100%) to an organophosphate, the Chlorpyrifos-methyl, was observed at the different sites. Three (3) species of the An. gambiae complex were identified: An. gambiae s.s, An. coluzzii and An. arabiensis. The frequencies of the kdr-w mutation were highly widespread (0.66 to 0.98) among the three species of the complex. The ace-1 mutation was detected at low frequencies (0 to 0.12) in An. gambiae s.s and An. coluzzii. A high level of GSTs and NSEs were observed within the different populations of the An. gambiae complex. Several mechanisms of insecticide resistance were found simultaneously in the same populations of An. gambiae complex conferring high multi-resistance to DDT, Carbamate and Pyrethroids. The full susceptibility of An. gambiae complex to organophosphates is a useful data for the national malaria control program in selecting the most appropriate products to both maintain the effectiveness of vector control strategies and best manage insecticide resistance as well as developing new alternative strategies for the control of major malaria vectors in Burkina Faso.