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The response to recent dengue outbreaks in Burkina Faso was insecticide-based, despite poor knowledge of the vector population's susceptibility to the insecticides used. Here, we report on the susceptibility to the main insecticide classes and identify important underlying mechanisms in Aedes aegypti populations in Ouagadougou and Banfora, in 2019 and 2020. Wild Ae. aegypti were tested as adults in WHO bioassays and then screened in real time melting curve qPCR analyses to genotype the F1534C, V1016I, and V410L Aedes kdr mutations. Ae. aegypti showed moderate resistance to 0.1% bendiocarb (80-95% survival post-exposure), 0.8% Malathion (60-100%), 0.21% pirimiphos-methyl (75% - 97%), and high resistance to 0.03% deltamethrin (20-70%). PBO pre-exposure partially restored pyrethroid susceptibility. Genotyping detected high frequency of 1534C allele (0.92) and moderate 1016I (0.1-0.32). The V410L mutation was detected in Burkina Faso for the first time (frequency 0.1-0.36). Mosquitoes surviving 4 h exposure to 0.03% deltamethrin had significantly higher frequencies of the F1534C mutation than dead mosquitoes (0.70 vs. 0.96, p 0.0001) and mosquitoes surviving 2 - 4 h exposure had a significantly reduced life span. Ae. aegypti from Burkina Faso are resistant to multiple insecticide classes with multiple mechanisms involved, demonstrating the essential role of insecticide resistance monitoring within national dengue control programmes.

Background: Malaria remains a major public health threat in Burkina Faso. In most sub-Saharan African countries, malaria control relies mainly on long-lasting insecticide-treated nets (LLINs) and indoor residual spray (IRS). In Burkina Faso, long-term selection pressure exerted on malaria vectors by insecticide used in agriculture, has been exacerbated by countrywide LLINs distribution campaigns conducted every three years since 2010. The current study investigated insecticide resistance and the mechanisms involved in the malaria vector populations of the Anopheles gambiae complex in urban localities of Ouagadougou, Burkina Faso. Methods: Anopheles gambiae s. l. larvae were collected from three localities of Ouagadougou from July to September 2018, and reared in the laboratory to adults. The susceptibility profile to pyrethroid, carbamate, and organophosphate insecticides was assessed using World Health Organization (WHO) tube assays. PCR was used for mosquito species identification and to detect insecticide target-site mutations involved in insecticide resistance. Results: More than 95% of the collected An. gambiae s. l. were identified as An. arabiensis. WHO susceptibility assays revealed that, in all localities, An. arabiensis displayed high resistance to permethrin and deltamethrin (mortalities both kdr mutations 1014F (0.81) and 1014S (0.18) were recorded, although carbamate and organophosphate-associated Ace-1 119S mutation was not found. Conclusion: High pyrethroid resistance, underpinned, at least in part by high-frequency knockdown resistance mutations, in the urban malaria vector population suggests the potentially poor performance of pyrethroid-only LLINs in the cities where they are distributed. This result supported the switch to next generation LLINs, which are not solely reliant on pyrethroids to kill host-seeking mosquitoes in the cities of Burkina Faso.

Background In rural Burkina Faso, the primary malaria vector Anopheles gambiae sensu lato (s.l.) primarily feeds indoors at night. Identification of factors which influence mosquito house entry could lead to development of novel malaria vector control interventions. A study was therefore carried out to identify risk factors associated with house entry of An. gambiae s.l. in south-west Burkina Faso, an area of high insecticide resistance. Methods Mosquitoes were sampled monthly during the malaria transmission season using CDC light traps in 252 houses from 10 villages, each house sleeping at least one child aged five to 15 years old. Potential risk factors for house entry of An. gambiae s.l. were measured, including socio-economic status, caregiver’s education and occupation, number of people sleeping in the same part of the house as the child, use of anti-mosquito measures, house construction and fittings, proximity of anopheline aquatic habitats and presence of animals near the house. Mosquito counts were compared using a generalized linear mixed-effect model with negative binomial and log link function, adjusting for repeated collections. Results 20,929 mosquitoes were caught, of which 16,270 (77.7%) were An. gambiae s.l. Of the 6691 An. gambiae s.l. identified to species, 4101 (61.3%) were An. gambiae sensu stricto and 2590 (38.7%) Anopheles coluzzii. Having a metal-roof on the child’s sleeping space (IRR = 0.55, 95% CI 0.32–0.95, p = 0.03) was associated with fewer malaria vectors inside the home. Conclusion This study demonstrated that the rate of An. gambiae s.l. was 45% lower in sleeping spaces with a metal roof, compared to those with thatch roofs. Improvements in house construction, including installation of metal roofs, should be considered in endemic areas of Africa to reduce the burden of malaria.

Before the release of genetically-modified or sterile male mosquitoes in an attempt to control local populations of malaria vectors, it is crucial to determine male traits involved in mating success. The effects of male size and age as determinants of male mating success in Anopheles gambiae s.s. were measured in the field and under laboratory conditions in Burkina Faso. First, the body sizes (estimated by wing length) of mating, swarming, and indoor-resting male mosquitoes were compared over a 3-yr period (2006–2009) from July to October in Soumousso and Vallee du Kou, two villages in western Burkina Faso. Second, the age structure of swarming and resting male mosquitoes were characterized based on the number of spermatocysts and the proportion of sperm in the reservoir of wild-caught male testis. Third, male age effects on the insemination rate of female An. gambiae were investigated in the laboratory. The mean size of males collected in copula was significantly larger than the mean for swarming males and indoor-resting males. The optimum male age for successful insemination of females was 4–8 d. These results suggest that male size is an important trait in determining male mating competitiveness in the field. Although age was not found to be a significant factor in mating competitiveness, it was significantly correlated with swarming behaviors in the field and insemination success in the laboratory. The implications of these results in terms of sexual selection in An. gambiae and vector control programs are further discussed.

An entomological survey was carried out at 15 sites dispersed throughout the three eco-climatic regions of Burkina Faso (West Africa) in order to assess the current distribution and frequency of mutations that confer resistance to insecticides in An. gambiae s.l. populations in the country. Both knockdown (kdr) resistance mutation variants (L1014F and L1014S), that confer resistance to pyrethroid insecticides, were identified concomitant with the ace-1 G119S mutation confirming the presence of multiple resistance mechanisms in the An. gambiae complex in Burkina Faso. Compared to the last survey, the frequency of the L1014F kdr mutation appears to have remained largely stable and relatively high in all species. In contrast, the distribution and frequency of the L1014S mutation has increased significantly in An. gambiae s.l. across much of the country. Furthermore we report, for the first time, the identification of the ace.1 G119S mutation in An. arabiensis populations collected at 8 sites [corrected]. This mutation, which confers resistance to organophosphate and carbamate insecticides, has been reported previously only in the An. gambiae S and M molecular forms. This finding is significant as organophosphates and carbamates are used in indoor residual sprays (IRS) to control malaria vectors as complementary strategies to the use of pyrethroid impregnated bednets. The occurrence of the three target-site resistance mutations in both An. gambiae molecular forms and now An. arabiensis has significant implications for the control of malaria vector populations in Burkina Faso and for resistance management strategies based on the rotation of insecticides with different modes of action.

Before the release of genetically-modified or sterile male mosquitoes in an attempt to control local populations of malaria vectors, it is crucial to determine male traits involved in mating success. The effects of male size and age as determinants of male mating success in Anopheles gambiae s.s. were measured in the field and under laboratory conditions in Burkina Faso. First, the body sizes (estimated by wing length) of mating, swarming, and indoor-resting male mosquitoes were compared over a 3-yr period (2006-2009) from July to October in Soumousso and Vallée du Kou, two villages in western Burkina Faso. Second, the age structure of swarming and resting male mosquitoes were characterized based on the number of spermatocysts and the proportion of sperm in the reservoir of wild-caught male testis. Third, male age effects on the insemination rate of female An. gambiae were investigated in the laboratory. The mean size of males collected in copula was significantly larger than the mean for swarming males and indoor-resting males. The optimum male age for successful insemination of females was 4-8 d. These results suggest that male size is an important trait in determining male mating competitiveness in the field. Although age was not found to be a significant factor in mating competitiveness, it was significantly correlated with swarming behaviors in the field and insemination success in the laboratory. The implications of these results in terms of sexual selection in An. gambiae and vector control programs are further discussed.

Background Historical studies have indicated that An. gambiae s.s. is the predominant malaria vector species in Bobo-Dioulasso the second biggest city of Burkina Faso (West Africa). However, over the last decade, An. arabiensis appears to be replacing An. gambiae s.s. as the most prevalent malaria vector in this urban setting. To investigate this species transition in more detail the present study aims to provide an update on the malaria vector composition in Bobo-Dioulasso, and also the Plasmodium infection rates and susceptibility to insecticides of the local An. gambiae s.l. population. Methods An entomological survey was carried out from May to December 2008 in Dioulassoba and Kodeni (central and peripheral districts respectively), which are representative of the main ecological features of the city. Sampling consisted of the collection of larval stages from water bodies, and adults by monthly indoor residual spraying (IRS) using aerosol insecticides. Insecticide susceptibility tests were performed using the WHO filter paper protocol on adults emerged from larvae. PCR was used to determine vector species and to identify resistance mechanisms (kdr and ace-1 R ). The Plasmodium infection rate was estimated by ELISA performed on female mosquitoes collected indoors by IRS. Results An. arabiensis was found to be the major malaria vector in Bobo-Dioulasso, comprising 50 to 100% of the vector population. The sporozoite infection rate for An. arabiensis was higher than An. gambiae s.s. at both Dioulassoba and Kodeni. An. gambiae s.l. was resistant to DDT and cross-resistant to pyrethroids at the two sites with higher levels of resistance observed in An. gambiae s.s. than An. arabiensis. Resistance to 0.1% bendiocarb was observed in the An. gambiae s.s. S form but not the M form or in An. arabiensis. The L1014F kdr mutation was detected in the two molecular forms of An. gambiae s.s. at varying frequencies (0.45 to 0.92), but was not detected in An. arabiensis, suggesting that other mechanisms are involved in DDT resistance in this species. The ace-1 R mutation was only detected in the S molecular form and was observed at the two sites at similar frequency (0.3). Conclusions Over the last ten years, An. arabiensis has become the major malaria vector in Bobo-Dioulasso city where it was formerly present only at low frequency. However, the ecological determinant that enhances the settlement of this species into urban and peri-urban areas of Bobo-Dioulasso remains to be clarified. The impact of the changing An. gambiae s.l. population in this region for vector control including resistance management strategies is discussed.

In the city of Bobo-Dioulasso in Burkina Faso, Anopheles arabiensis has superseded Anopheles gambiae s.s. as the major malaria vector and the larvae are found in highly polluted habitats normally considered unsuitable for Anopheles mosquitoes. Here we show that An. gambiae s.l. adults emerging from a highly polluted site in the city centre (Dioulassoba) have a high prevalence of DDT resistance (percentage mortality after exposure to diagnostic dose = 65.8% in the dry season and 70.4% in the rainy season, respectively). An investigation into the mechanisms responsible found an unexpectedly high frequency of the 1014S kdr mutation (allele frequency = 0.4), which is found at very low frequencies in An. arabiensis in the surrounding rural areas, and an increase in transcript levels of several detoxification genes, notably from the glutathione transferase and cytochrome P450 gene families. A number of ABC transporter genes were also expressed at elevated levels in the DDT resistant An. arabiensis. Unplanned urbanisation provides numerous breeding grounds for mosquitoes. The finding that Anopheles mosquitoes adapted to these urban breeding sites have a high prevalence of insecticide resistance has important implications for our understanding of the selective forces responsible for the rapid spread of insecticide resistant populations of malaria vectors in Africa.

Background Several cases of malaria are frequently recorded during the dry period in Ouagadougou town (Burkina Faso). This has led to the design of a series of studies focusing on both parasitological and entomological investigations intended to provide relevant health data on the risk of local malaria transmission according to the way of urbanisation. Methods A cross-sectional entomological survey was carried out in various districts of Ouagadougou in April and October 2006. Adult malaria vectors were collected using CDC traps and indoor insecticide spraying performed in four houses during four consecutive days/nights. Intensive larval sampling was also done in available water ponds throughout the study sites. Results In April, the anopheline breeding sites consisted only of semi-permanent or permanent swamps located mainly in the two peripheral districts. Despite the presence of anopheline larvae in these breeding sites, less than five Anopheles gambiae s.l. adults were caught by CDC traps and indoor insecticide spraying. In October, additionally to the permanent breeding sites reported in April, some rainfall swamps were also found positive to anophelines. The number of adults' mosquitoes was higher than that collected in April (2 vs 159 in October). Out of 115 larvae of An. gambiae s.l. analysed by PCR in April, 59.1% (68/115) were identified as Anopheles arabiensis, 39.1% (45/115) as An. gambiae M while the S form represented less than 2%. Overall 120 larvae and 86 females were identified by PCR in October as An. gambiae M form (51%) and An. arabiensis (42.2%). The S form represented only 6.8%. The global sporozoite rate recorded was high (6.8%) and did not differ between the districts except in the central district where no positive mosquito was detected. Conclusion Although only few adults' mosquitoes were actively caught during the driest month, malaria vectors persisted all year long that increases the risk of urban malaria transmission. The distribution of breeding sites and especially the occurrence of malaria vectors were more abundant in the periphery, which is more like that of a rural settlement. The evolution of malaria prevalence and the factors sustaining the risk of transmission in Ouagadougou as well in many African cities during the dry season are discussed.

One of the greatest challenges in reducing malaria transmission in sub-Saharan Africa is the high degree of plasticity in the behaviour and ecology of members of the Anopheles gambiae complex, which includes the most efficient malaria vectors globally. For example, in areas of West Africa, sympatric populations of the M and S molecular forms of An. gambiae s.s. have diverged into recognized species (An. coluzzii Coetzee & Wilkerson sp.n. and the nominative species, An. gambiae s.s., respectively) through ecological speciation. Whereas the main breeding sites for An. gambiae s.s. continue to be temporary water bodies, An. coluzzii has become adapted to breeding well in irrigated fields, which has led to increases in relative abundance and duration of breeding seasons, and, hence, an enhancement of malaria transmission throughout the year. Thus, an increase in malaria prevalence is associated with a process of speciation that gave rise relatively rapidly to a new vector species highly adapted to a new breeding habitat created by changes in agricultural practice. To face this challenge, it is important that we understand the mechanisms by which this kind of speciation occurs. There is good evidence that speciation in this case has involved reproductive isolation, and, therefore, a five year study of sympatric populations of the M and S molecular forms in the Bobo Dioulasso area of Burkina Faso was undertaken to identify mechanisms that limit cross-matings. Mating in the An. gambiae complex generally occurs in swarms consisting mainly of males, which form at specific times of day at consistent sites defined by physical features in the environment, e.g., over wells, piles of wood, clearings in vegetation. More than 1,000 mating swarms were documented; a measurable degree of reproductive isolation could be explained by significant differences between species in seasonal abundance, characteristics of swarm sites and daily timing (circadian rhythm) of swarming. Although these factors each contribute to a reduced likelihood that males and females of ‘opposite’ molecular form encounter each other at close range in a mating swarm, both species were occasionally found in mixed swarms. All of the females caught in mixed swarms, however, had been inseminated by a conspecific male. Hence, further research is required to establish the close-range mechanism(s) of species recognition that seem to occur within swarms, such as auditory communication, that lead to assortative mating.