Whole-genome sequencing of major malaria vectors reveals the evolution of new insecticide resistance variants in a longitudinal study in Burkina Faso.

BACKGROUND: Intensive deployment of insecticide based malaria vector control tools resulted in the rapid evolution of phenotypes resistant to these chemicals. Understanding this process at the genomic level is important for the deployment of successful vector control interventions. Therefore, longitudinal sampling followed by whole genome sequencing (WGS) is necessary to understand how these evolutionary processes evolve over time. This study investigated the change in genetic structure and the evolution of the insecticide resistance variants in natural populations of Anopheles gambiae over time and space from 2012 to 2017 in Burkina Faso. METHODS: New genomic data have been generated from An. gambiae mosquitoes collected from three villages in the western part of Burkina Faso between 2012 and 2017. The samples were whole-genome sequenced and the data used in the An. gambiae 1000 genomes (Ag1000G) project as part of the Vector Observatory. Genomic data were analysed using the analysis pipeline previously designed by the Ag1000G project. RESULTS: The results showed similar and consistent nucleotide diversity and negative Tajima's D between An. gambiae sensu stricto (s.s.) and Anopheles coluzzii. Principal component analysis (PCA) and the fixation index (FST) showed a clear genetic structure in the An. gambiae sensu lato (s.l.) species. Genome-wide FST and H12 scans identified genomic regions under divergent selection that may have implications in the adaptation to ecological changes. Novel voltage-gated sodium channel pyrethroid resistance target-site alleles (V402L, I1527T) were identified at increasing frequencies alongside the established alleles (Vgsc-L995F, Vgsc-L995S and N1570Y) within the An. gambiae s.l. POPULATIONS: Organophosphate metabolic resistance markers were also identified, at increasing frequencies, within the An. gambiae s.s. populations from 2012 to 2017, including the SNP Ace1-G280S and its associated duplication. Variants simultaneously identified in the same vector populations raise concerns about the long-term efficacy of new generation bed nets and the recently organophosphate pirimiphos-methyl indoor residual spraying in Burkina Faso. CONCLUSION: These findings highlighted the benefit of genomic surveillance of malaria vectors for the detection of new insecticide resistance variants, the monitoring of the existing resistance variants, and also to get insights into the evolutionary processes driving insecticide resistance.

Symbiotic bacteria Sodalis glossinidius, Spiroplasma sp and Wolbachia do not favour Trypanosoma grayi coexistence in wild population of tsetse flies collected in Bobo-Dioulasso, Burkina Faso.

Background: Tsetse flies, the biological vectors of African trypanosomes, have established symbiotic associations with different bacteria. Their vector competence is suggested to be affected by bacterial endosymbionts. The current study provided the prevalence of three tsetse symbiotic bacteria and trypanosomes in Glossina species from Burkina Faso. Results: A total of 430 tsetse flies were captured using biconical traps in four different collection sites around Bobo-Dioulasso (Bama, Bana, Nasso, and Peni), and their guts were removed. Two hundred tsetse were randomly selected and their guts were screened byPCR for the presence of Sodalis glossinidius, Spiroplasmasp., Wolbachia and trypanosomes. Of the 200 tsetse, 196 (98.0%) were Glossina palpalis gambienseand 4 (2.0%) Glossina tachinoides. The overall symbiont prevalence was 49.0%, 96.5%, and 45.0%, respectively for S. glossinidius, Spiroplasma and Wolbachia. Prevalence varied between sampling locations: S. glossinidius(54.7%, 38.5%, 31.6%, 70.8%); Spiroplasma (100%, 100%, 87.7%, 100%); and Wolbachia(43.4%, 38.5%, 38.6%, 70.8%),respectively in Bama, Bana, Nasso and Peni. Noteworthy, no G. tachhnoideswas infected by S. glossinidius and Wolbachia, but they were all infected by Spiroplasma sp. A total of 196 (98.0 %) harbored at least one endosymbionts. Fifty-five (27.5%) carried single endosymbiont. Trypanosomes were found only in G.p. gambiense, but not G. tachinoides. Trypanosomes were present in flies from all study locations with an overall prevalence of 29.5%. In Bama, Bana, Nasso, and Peni, the trypanosome infection rate was respectively 39.6%, 23.1%, 8.8%, and 37.5%. Remarkably, only Trypanosoma grayi was present. Of all trypanosome-infected flies, 55.9%, 98.3%, and 33.9% hosted S. glossinidius, Spiroplasma sp and Wolbachia, respectively. There was no association between Sodalis, Spiroplasma and trypanosome presence, but there was a negative association with Wolbachia presence. We reported1.9 times likelihood of trypanosome absence when Wolbachia was present. Conclusion: This is the first survey reporting the presence of Trypanosoma grayi in tsetse from Burkina Faso. Tsetse from these localities were highly positive for symbiotic bacteria, more predominantly with Spiroplasma sp. Modifications of symbiotic interactions may pave way for disease control.

Symbiotic bacteria Sodalis glossinidius, Spiroplasma sp and Wolbachia do not favour Trypanosoma grayi coexistence in wild population of tsetse flies collected in Bobo-Dioulasso, Burkina Faso.

BACKGROUND: Tsetse flies, the biological vectors of African trypanosomes, have established symbiotic associations with different bacteria. Their vector competence is suggested to be affected by bacterial endosymbionts. The current study provided the prevalence of three tsetse symbiotic bacteria and trypanosomes in Glossina species from Burkina Faso. RESULTS: A total of 430 tsetse flies were captured using biconical traps in four different collection sites around Bobo-Dioulasso (Bama, Bana, Nasso, and Peni), and their guts were removed. Two hundred tsetse were randomly selected and their guts were screened by PCR for the presence of Sodalis glossinidius, Spiroplasma sp., Wolbachia and trypanosomes. Of the 200 tsetse, 196 (98.0%) were Glossina palpalis gambiensis and 4 (2.0%) Glossina tachinoides. The overall symbiont prevalence was 49.0%, 96.5%, and 45.0%, respectively for S. glossinidius, Spiroplasma and Wolbachia. Prevalence varied between sampling locations: S. glossinidius (54.7%, 38.5%, 31.6%, 70.8%); Spiroplasma (100%, 100%, 87.7%, 100%); and Wolbachia (43.4%, 38.5%, 38.6%, 70.8%), respectively in Bama, Bana, Nasso and Peni. Noteworthy, no G. tachnoides was infected by S. glossinidius and Wolbachia, but they were all infected by Spiroplasma sp. A total of 196 (98.0%) harbored at least one endosymbionts. Fifty-five (27.5%) carried single endosymbiont. Trypanosomes were found only in G. p. gambiensis, but not G. tachinoides. Trypanosomes were present in flies from all study locations with an overall prevalence of 29.5%. In Bama, Bana, Nasso, and Peni, the trypanosome infection rate was respectively 39.6%, 23.1%, 8.8%, and 37.5%. Remarkably, only Trypanosoma grayi was present. Of all trypanosome-infected flies, 55.9%, 98.3%, and 33.9% hosted S. glossinidius, Spiroplasma sp and Wolbachia, respectively. There was no association between Sodalis, Spiroplasma and trypanosome presence, but there was a negative association with Wolbachia presence. We reported 1.9 times likelihood of trypanosome absence when Wolbachia was present. CONCLUSION: This is the first survey reporting the presence of Trypanosoma grayi in tsetse from Burkina Faso. Tsetse from these localities were highly positive for symbiotic bacteria, more predominantly with Spiroplasma sp. Modifications of symbiotic interactions may pave way for disease control.

Wolbachia confers protection against the entomopathogenic fungus Metarhizium pingshaense in African Aedes aegypti.

Symbiotic and pathogenic microorganisms such as bacteria and fungi represent promising alternatives to chemical insecticides to respond to the rapid increase of insecticide resistance and vector-borne disease outbreaks. This study investigated the interaction of two strains of Wolbachia, wAlbB and wAu, with the natural entomopathogenic fungi from Burkina Faso Metarhizium pingshaense, known to be lethal against Anopheles mosquitoes. In addition to showing the potential of Metarhizium against African Aedes aegypti wild-type populations, our study shows that the wAlbB and wAu provide a protective advantage against entomopathogenic fungal infections. Compared to controls, fungal-infected wAu and wAlbB-carrying mosquitoes showed higher longevity, without any significant impact on fecundity and fertility phenotypes. This study provides new insights into the complex multipartite interaction among the mosquito host, the Wolbachia endosymbiont and the entomopathogenic fungus that might be employed to control mosquito populations. Future research should investigate the fitness costs of Wolbachia, as well as its spread and prevalence within mosquito populations. Additionally, evaluating the impact of Wolbachia on interventions involving Metarhizium pingshaense through laboratory and semi-field population studies will provide valuable insights into the effectiveness of this combined approach.

Considerations for first field trials of low-threshold gene drive for malaria vector control.

Sustainable reductions in African malaria transmission require innovative tools for mosquito control. One proposal involves the use of low-threshold gene drive in Anopheles vector species, where a 'causal pathway' would be initiated by (i) the release of a gene drive system in target mosquito vector species, leading to (ii) its transmission to subsequent generations, (iii) its increase in frequency and spread in target mosquito populations, (iv) its simultaneous propagation of a linked genetic trait aimed at reducing vectorial capacity for Plasmodium, and (v) reduced vectorial capacity for parasites in target mosquito populations as the gene drive system reaches fixation in target mosquito populations, causing (vi) decreased malaria incidence and prevalence. Here the scope, objectives, trial design elements, and approaches to monitoring for initial field releases of such gene dive systems are considered, informed by the successful implementation of field trials of biological control agents, as well as other vector control tools, including insecticides, Wolbachia, larvicides, and attractive-toxic sugar bait systems. Specific research questions to be addressed in initial gene drive field trials are identified, and adaptive trial design is explored as a potentially constructive and flexible approach to facilitate testing of the causal pathway. A fundamental question for decision-makers for the first field trials will be whether there should be a selective focus on earlier points of the pathway, such as genetic efficacy via measurement of the increase in frequency and spread of the gene drive system in target populations, or on wider interrogation of the entire pathway including entomological and epidemiological efficacy. How and when epidemiological efficacy will eventually be assessed will be an essential consideration before decisions on any field trial protocols are finalized and implemented, regardless of whether initial field trials focus exclusively on the measurement of genetic efficacy, or on broader aspects of the causal pathway. Statistical and modelling tools are currently under active development and will inform such decisions on initial trial design, locations, and endpoints. Collectively, the considerations here advance the realization of developer ambitions for the first field trials of low-threshold gene drive for malaria vector control within the next 5 years.

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.

The paradox of plant preference: The malaria vectors Anopheles gambiae and Anopheles coluzzii select suboptimal food sources for their survival and reproduction.

Anopheles gambiae and Anopheles coluzzii mosquitoes, two major malaria vectors in sub-Saharan Africa, exhibit selectivity among plant species as potential food sources. However, it remains unclear if their preference aligns with optimal nutrient intake and survival. Following an extensive screening of the effects of 31 plant species on An. coluzzii in Burkina Faso, we selected three species for their contrasting effects on mosquito survival, namely Ixora coccinea, Caesalpinia pulcherrima, and Combretum indicum. We assessed the sugar content of these plants and their impact on mosquito fructose positivity, survival, and insemination rate, using Anopheles coluzzii and Anopheles gambiae, with glucose 5% and water as controls. Plants displayed varying sugar content and differentially affected the survival, sugar intake, and insemination rate of mosquitoes. All three plants were more attractive to mosquitoes than controls, with An. gambiae being more responsive than An. coluzzii. Notably, C. indicum was the most attractive but had the lowest sugar content and offered the lowest survival, insemination rate, and fructose positivity. Our findings unveil a performance-preference mismatch in An. coluzzii and An. gambiae regarding plant food sources. Several possible reasons for this negative correlation between performance and preference are discussed.

Wolbachia strain wAlbB shows favourable characteristics for dengue control use in Aedes aegypti from Burkina Faso.

Dengue represents an increasing public health burden worldwide. In Africa, underreporting and misdiagnosis often mask its true epidemiology, and dengue is likely to be both more widespread than reported data suggest and increasing in incidence and distribution. Wolbachia-based dengue control is underway in Asia and the Americas but has not to date been deployed in Africa. Due to the genetic heterogeneity of African Aedes aegypti populations and the complexity of the host-symbiont interactions, characterization of key parameters of Wolbachia-carrying mosquitoes is paramount for determining the potential of the system as a control tool for dengue in Africa. The wAlbB Wolbachia strain was stably introduced into an African Ae. aegypti population by introgression, and showed high intracellular density in whole bodies and different mosquito tissues; high intracellular density was also maintained following larval rearing at high temperatures. No effect on the adult lifespan induced by Wolbachia presence was detected. Moreover, the ability of this strain to strongly inhibit DENV-2 dissemination and transmission in the host was also demonstrated in the African background. Our findings suggest the potential of harnessing Wolbachia for dengue control for African populations of Ae. aegypti.

First identification of Microsporidia MB in Anopheles coluzzii from Zinder City, Niger.

BACKGROUND: Malaria, a disease transmitted by Anopheles mosquitoes, is a major public health problem causing millions of deaths worldwide, mostly among children under the age of 5 years. Biotechnological interventions targeting parasite-vector interactions have shown that the microsporidian symbiont Microsporidia MB has the potential to disrupt and block Plasmodium transmission. METHODS: A prospective cross-sectional survey was conducted in Zinder City (Zinder), Niger, from August to September 2022, using the CDC light trap technique to collect adult mosquitoes belonging to the Anopheles gambiae complex. The survey focused on collecting mosquitoes from three neighborhoods of Zinder (Birni, Kangna and Garin Malan, located in communes I, II and IV, respectively). Collected mosquitoes were sorted and preserved in 70% ethanol. PCR was used to identify host species and detect the presence of Microsporidia MB and Plasmodium falciparum infection. RESULTS: Of the 257 Anopheles mosquitoes collected and identified by PCR, Anopheles coluzzii was the most prevalent species, accounting for 97.7% of the total. Microsporidia MB was exclusively detected in A. coluzzii, with a prevalence of 6.8% (17/251) among the samples. No significant difference in prevalence was found among the three neighborhoods. Only one An. coluzzii mosquito tested PCR-positive for P. falciparum. CONCLUSIONS: The results confirm the presence of Microsporidia MB in Anopheles mosquitoes in Zinder, Niger, indicating its potential use as a biotechnological intervention against malaria transmission. However, further studies are needed to determine the efficacy of Microsporidia MB to disrupt Plasmodium transmission as well as its impact on vector fitness.

Development of circulating isolates of Plasmodium falciparum is accelerated in Anopheles vectors with reduced reproductive output.

Anopheles gambiae and its sibling species Anopheles coluzzii are the most efficient vectors of the malaria parasite Plasmodium falciparum. When females of these species feed on an infected human host, oogenesis and parasite development proceed concurrently, but interactions between these processes are not fully understood. Using multiple natural P. falciparum isolates from Burkina Faso, we show that in both vectors, impairing steroid hormone signaling to disrupt oogenesis leads to accelerated oocyst growth and in a manner that appears to depend on both parasite and mosquito genotype. Consistently, we find that egg numbers are negatively linked to oocyst size, a metric for the rate of oocyst development. Oocyst growth rates are also strongly accelerated in females that are in a pre-gravid state, i.e. that fail to develop eggs after an initial blood meal. Overall, these findings advance our understanding of mosquito-parasite interactions that influence P. falciparum development in malaria-endemic regions.

Adhesion and virulence properties of native Metarhizium fungal strains from Burkina Faso for the control of malaria vectors.

BACKGROUND: Local strains of the entomopathogenic fungus Metarhizium pingshaense in Burkina Faso have demonstrated remarkable virulence against malaria vectors, positioning them as promising candidates for inclusion in the future arsenal of malaria control strategies. However, the underlying mechanisms responsible for this virulence remain unknown. To comprehend the fungal infection process, it is crucial to investigate the attachment mechanisms of fungal spores to the mosquito cuticle and explore the relationship between virulence and attachment kinetics. This study aims to assess the adhesion and virulence properties of native Metarhizium fungal strains from Burkina Faso for controlling malaria vectors. METHODS: Fungal strains were isolated from 201 insects and 1399 rhizosphere samples, and four strains of Metarhizium fungi were selected. Fungal suspensions were used to infect 3-day-old female Anopheles coluzzii mosquitoes at three different concentrations (106, 107, 108 conidia/ml). The survival of the mosquitoes was measured over 14 days, and fungal growth was quantified after 1 and 24 h to assess adhesion of the fungal strains onto the mosquito cuticle. RESULTS: All four fungi strains increased mosquito mortality compared to control (Chi-square test, χ2 = 286.55, df = 4, P < 0.001). Adhesion of the fungal strains was observed on the mosquito cuticle after 24 h at high concentrations (1 × 108 conidia/ml), with one strain, having the highest virulent, showing adhesion after just 1 h. CONCLUSION: The native strains of Metarhizium spp. fungi found in Burkina Faso have the potential to be effective biocontrol agents against malaria vectors, with some strains showing high levels of both virulence and adhesion to the mosquito cuticle.

Key considerations, target product profiles, and research gaps in the application of infrared spectroscopy and artificial intelligence for malaria surveillance and diagnosis.

Studies on the applications of infrared (IR) spectroscopy and machine learning (ML) in public health have increased greatly in recent years. These technologies show enormous potential for measuring key parameters of malaria, a disease that still causes about 250 million cases and 620,000 deaths, annually. Multiple studies have demonstrated that the combination of IR spectroscopy and machine learning (ML) can yield accurate predictions of epidemiologically relevant parameters of malaria in both laboratory and field surveys. Proven applications now include determining the age, species, and blood-feeding histories of mosquito vectors as well as detecting malaria parasite infections in both humans and mosquitoes. As the World Health Organization encourages malaria-endemic countries to improve their surveillance-response strategies, it is crucial to consider whether IR and ML techniques are likely to meet the relevant feasibility and cost-effectiveness requirements-and how best they can be deployed. This paper reviews current applications of IR spectroscopy and ML approaches for investigating malaria indicators in both field surveys and laboratory settings, and identifies key research gaps relevant to these applications. Additionally, the article suggests initial target product profiles (TPPs) that should be considered when developing or testing these technologies for use in low-income settings.

Characterization of the swarming behavior of Anopheles coluzzii and Anopheles gambiae (Diptera: Culicidae) populations in a hybrid zone of Senegal.

Anopheles gambiae and Anopheles coluzzii, often found in sympatry and synchronous, have undergone a premating reproductive isolation across their distribution range. However, in the Western coast of Africa, unexpected hybridization zones have been observed, and little is known about swarming behavior of these cryptic taxa. Here, we characterized the swarming behavior of An. coluzzii and An. gambiae to investigate its role in the high hybridization level in Senegal. The study was conducted in the south and central Senegal during the 2018 rainy season. Mating swarms of malaria vectors were surveyed at sunset and collected using an insect net. Meanwhile, indoor resting populations of malaria vectors were collected by pyrethrum spray catches. Upon collection, specimens were identified morphologically, and then members of the An. gambiae complex were identified at the species level by polymerase chain reaction (PCR). An. gambiae swarmed mainly over bare ground, whereas An. coluzzii were found swarming above various objects creating a dark-light contrast with the bare ground. The swarms height varied from 0.5 to 2.5 m. Swarming starting time was correlated with sunset whatever the months for both species, and generally lasted about 10 min. No mixed swarm of An. gambiae and An. coluzzii was found even in the high hybridization area. These results indicated a premating isolation between An. coluzzii and An. gambiae. However, the high hybridization rate in the sympatric area suggests that heterogamous mating is occurring, thus stressing the need for further extensive studies.

Delftia tsuruhatensis TC1 symbiont suppresses malaria transmission by anopheline mosquitoes.

Malaria control demands the development of a wide range of complementary strategies. We describe the properties of a naturally occurring, non-genetically modified symbiotic bacterium, Delftia tsuruhatensis TC1, which was isolated from mosquitoes incapable of sustaining the development of Plasmodium falciparum parasites. D. tsuruhatensis TC1 inhibits early stages of Plasmodium development and subsequent transmission by the Anopheles mosquito through secretion of a small-molecule inhibitor. We have identified this inhibitor to be the hydrophobic molecule harmane. We also found that, on mosquito contact, harmane penetrates the cuticle, inhibiting Plasmodium development. D. tsuruhatensis TC1 stably populates the mosquito gut, does not impose a fitness cost on the mosquito, and inhibits Plasmodium development for the mosquito's life. Contained field studies in Burkina Faso and modeling showed that D. tsuruhatensis TC1 has the potential to complement mosquito-targeted malaria transmission control.

Spatial modelling of malaria prevalence associated with geographical factors in Houet province of Burkina Faso, West Africa.

Malaria is a permanent threat to health in western Burkina Faso. Research has shown that geographical variables contribute to the spatial distribution in its transmission. The objective of this study is to assess the relationship between malaria prevalence and potential explanatory geographical variables in the Houet province in Burkina Faso. Statistics on malaria prevalence registered by health centres in the Houet province in 2017 and potential geographical variables identified through a literature review were collected. An Ordinary Least Squares (OLS) regression was used to identify key geographical variables and to measure their association with malaria while the Getis Ord Gi* index was used to locate malaria hotspots. The results showed that average annual temperature, vegetation density, percentage of clay in the soil, total annual rainfall and distance to the nearest waterbody are the main variables associated with malaria prevalence. These variables account for two-thirds of the spatial variability of malaria prevalence observed in Houet province. The intensity and direction of the relationship between malaria prevalence and geographical factors vary according to the variable. Hence, only vegetation density is positively correlated with malaria prevalence. Average temperature, for soil clay content, annual rainfall and for distance to the nearest water body are negatively correlated with the disease prevalence. These results show that even in an endemic area, malaria prevalence has significant spatial variation. The results could contribute to the choice of intervention sites, as this choice is crucial for reducing the malaria burden. Supplementary Information: The online version contains supplementary material available at 10.1007/s10708-022-10692-7.

Infection of the malaria vector Anopheles coluzzii with the entomopathogenic bacteria Chromobacterium anophelis sp. nov. IRSSSOUMB001 reduces larval survival and adult reproductive potential.

BACKGROUND: Vector control tools are urgently needed to control malaria transmission in Africa. A native strain of Chromobacterium sp. from Burkina Faso was recently isolated and preliminarily named Chromobacterium anophelis sp. nov. IRSSSOUMB001. In bioassays, this bacterium showed a promising virulence against adult mosquitoes and reduces their blood feeding propensity and fecundity. The current study assessed the entomopathogenic effects of C. anophelis IRSSSOUMB001 on larval stages of mosquitoes, as well as its impacts on infected mosquitoes reproductive capacity and trans-generational effects. METHODS: Virulence on larvae and interference with insemination were assayed by co-incubation with C. anophelis IRSSSOUMB001 at a range of 104 to 108 cfu/ml. Trans-generational effects were determined by measuring body size differences of progeny from infected vs. uninfected parent mosquitoes using wing size as a proxy. RESULTS: Chromobacterium anophelis IRSSSOUMB001 killed larvae of the pyrethroid-resistant Anopheles coluzzii with LT80 of ~ 1.75 ± 0.14 days at 108 cfu/ml in larval breeding trays. Reproductive success was reduced as a measure of insemination rate from 95 ± 1.99% to 21 ± 3.76% for the infected females. There was a difference in wing sizes between control and infected mosquito offsprings from 2.55 ± 0.17 mm to 2.1 ± 0.21 mm in infected females, and from 2.43 ± 0.13 mm to 1.99 ± 0.15 mm in infected males. CONCLUSIONS: This study showed that C. anophelis IRSSSOUMB001 was highly virulent against larvae of insecticide-resistant Anopheles coluzzii, and reduced both mosquito reproduction capacity and offspring fitness. Additional laboratory, field, safety and social acceptance studies are needed to draw firm conclusions about the practical utility of this bacterial strain for malaria vector control.

Natural plant diet impacts phenotypic expression of pyrethroid resistance in Anopheles mosquitoes.

Success in reducing malaria transmission through vector control is threatened by insecticide resistance in mosquitoes. Although the proximal molecular mechanisms and genetic determinants involved are well documented, little is known about the influence of the environment on mosquito resistance to insecticides. The aim of this study was to assess the effect of plant sugar feeding on the response of Anopheles gambiae sensu lato to insecticides. Adults were fed with one of four treatments, namely a 5% glucose control solution, nectariferous flowers of Barleria lupulina, of Cascabela thevetia and a combination of both B. lupulina + C. thevetia. WHO tube tests were performed with 0.05% and 0.5% deltamethrin, and knockdown rate (KD) and the 24 h mosquito mortality were measured. Plant diet significantly influenced mosquito KD rate at both concentrations of deltamethrin. Following exposure to 0.05% deltamethrin, the B. lupulina diet induced a 2.5 fold-increase in mosquito mortality compared to 5% glucose. Species molecular identification confirmed the predominance of An. gambiae (60% of the samples) over An. coluzzii and An. arabiensis in our study area. The kdr mutation L1014F displayed an allelic frequency of 0.75 and was positively associated with increased phenotypic resistance to deltamethrin. Plant diet, particularly B. lupulina, increased the susceptibility of mosquitoes to insecticides. The finding that B. lupulina-fed control individuals (i.e. not exposed to deltamethrin) also displayed increased 24 h mortality suggests that plant-mediated effects may be driven by a direct effect of plant diet on mosquito survival rather than indirect effects through interference with insecticide-resistance mechanisms. Thus, some plant species may weaken mosquitoes, making them less vigorous and more vulnerable to the insecticide. There is a need for further investigation, using a wider range of plant species and insecticides, in combination with other relevant environmental factors, to better understand the expression and evolution of insecticide resistance.