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Agricultural use of insecticides is involved in the selection of resistance to these compounds in field populations of mosquitoes in Burkina Faso. Anopheles gambiae s.l. was resistant to permethrin and DDT in cotton-growing and urban areas, but susceptible in areas with limited insecticide selection pressure (rice fields and control areas). Neverth...
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Context 1
... area. The study was carried out in four localities in Burkina Faso chosen because of their different patterns of insecticide use (Figure 1). The localities were 1) a rice field cultivation area with two sampling sites, village VK5, located in the center of the rice fields and village VK7, located on the outskirts of the rice fields; 2) a cotton-growing area (Léna); 3) an urban area (Bobo-Dioulasso) with two sampling sites, Dsso ba, located in the center of the city and Kuinima, located on the outskirts of the city; and 4) a control area, Batié, a site with very limited use of insecticides. ...
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Background:
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Background
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Citations
... Indeed, LLIN coverage has already been associated with pyrethroid resistance of An. gambiae s.l. in Niger (Czeher et al., 2008). Excessive use of insecticides for crop protection has been mentioned as one of the main factors of selection pressure for mosquito resistanceespecially in An. gambiae s.l. in West Africa ( Diabate et al., 2002;Akogbeto et al., 2005;Yadouleton et al., 2009;Tia et al., 2017;Chabi et al., 2018;Salako et al., 2018;Orondo et al., 2021), specifically An. coluzzii, which tends to prefer agricultural areas, especially rice-growing areas, as larval sites. Mosquito larvae in rice fields undergo selection pressure from agricultural pesticides leading to the emergence of a resistant adult strains (Akogbeto et al., 2005). ...
Malaria vector control in Niger is currently based on the distribution of insecticide treated nets. However, vectors resistance to insecticides represents a major threat to the current national strategy against malaria. This study aims to characterize the impact of agroecosystems on insecticide resistance in Anopheles gambiae s.l. at Niamey. Larvae collected were reared until emergence. Adults aged 2-5 days were used to assess susceptibility to insecticides (pyrethroids, DDT and bendiocarb) after pre-exposure to piperonyl butoxide (PBO) synergist according to WHO protocols. PCRs were performed to identify the sibling species of An. gambiae complex and characterization resistance mutations (Kdr and ace-1). Overall, An. gambiae s.l. was resistance to pyrethroids and DDT (mortality rates from 1% to 55%) and susceptible to bendiocarb at most sites. Pre-exposure to the PBO synergist resulted in partial restoration of pyrethroid susceptibility. Two species of An. gambiae complex were found: An. arabiensis and An. coluzzii. The presence of An. coluzzii was strongly correlated with agricultural practices (99% in rice cultivation sites). Kdr mutations were found at all sites with kdr-w ranging from 45% to 70% in mosquitoes collected in unirrigated and rice field, respectively, and kdr-e found at 37% to 47% at each type of site, respectively. The ace-1 mutation was detected at low frequency (1%) and only from two rice cultivation sites. The high levels of pyrethroid and DDT resistance detected in Niamey had a strong link with rice cultivation, shown that agriculture is a driver of resistance that can compromise control malaria efforts. Keywords: Anopheles gambiae sensu lato, insecticide, resistance, agroecosystem, vector control, Niamey, Niger..
... However, this adaptation can be impacted directly or indirectly by many other alterations of the mosquito ecology associated with human activities and densities. In particular, the development of cities (or urbanization) and agriculture have been shown to have considerable impacts on the spread of resistance in Anopheles gambiae [58] and Aedes aegypti [20]. Insecticides are indeed widely used in agriculture to control diverse pests, but also select non-target resistant mosquitoes. ...
Background
Mosquitoes of the Culex pipiens complex are widely distributed vectors for several arboviruses affecting humans. Consequently, their populations have long been controlled using insecticides, in response to which different resistance mechanisms have been selected. Moreover, their ecological preferences and broad adaptability allow C. pipiens mosquitoes to breed in highly polluted water bodies where they are exposed to many residuals from anthropogenic activities. It has been observed for several mosquito species that anthropization (in particular urbanization and agricultural lands) can lead to increased exposure to insecticides and thus to increased resistance. The main objective of the present study was to investigate whether and how urbanization and/or agricultural lands had a similar impact on C. pipiens resistance to insecticides in Morocco.
Methods
Breeding sites were sampled along several transects in four regions around major Moroccan cities, following gradients of decreasing anthropization. The imprint of anthropogenic activities was evaluated around each site as the percentage of areas classified in three categories: urban, agricultural and natural. We then assessed the frequencies of four known resistance alleles in these samples and followed their dynamics in five urban breeding sites over 4 years.
Results
The distribution of resistance alleles revealed a strong impact of anthropization, in both agricultural and urbanized lands, although different between resistance mutations and between Moroccan regions; we did not find any clear trend in the dynamics of these resistance alleles during the survey.
Conclusions
Our study provides further evidence for the role of anthropic activities in the selection and maintenance of mutations selected for resistance to insecticides in mosquitoes. The consequences are worrying as this could decrease vector control capacities and thus result in epizootic and epidemic outbreaks. Consequently, concerted and integrated disease control strategies must be designed that include better management regarding the consequences of our activities.
Graphical Abstract
... The development and spread of malaria vector resistance to insecticides have been attributed to the intensive use of insecticides in agriculture, particularly in cotton cultivation [17,18]. ...
... Why exposure to ivermectin at the larval stage leads to a reduction in the time taken to oviposition remains puzzling and warrants further investigation as shortening the gonotrophic cycle would potentially affect the blood-feeding frequency of the adult mosquitoes and therefore affect vector human contact [28]. Exposure to insecticides in the larval stages has been reported to increase tolerance of the adult mosquitoes to insecticides [29,30]. In the current study, exposure to ivermectin in the third/fourth-instar larvae did not affect the susceptibility of the adults to ivermectin. ...
Background
The effects of ivermectin (endectocide) on mosquito survival make it a potential new malaria vector control tool. The drug can be administered to mosquito disease vectors through blood hosts that include humans and livestock. Its increased use may cause contamination of larval habitats, either directly through livestock excreta or indirectly through leaching or run-off from contaminated soil, albeit in sublethal doses. However, the effects of such exposure on immature stages and the subsequent adults that emerge are poorly understood. This study was undertaken to evaluate the impact of ivermectin exposure on Anopheles gambiae s.s. larvae and its effects on fitness and susceptibility to ivermectin in the emerging adults.
Methods
Laboratory-reared An. gambiae s.s. (Kilifi strain) larvae were exposed to five different ivermectin concentrations; 0, 0.00001, 0.0001, 0.001, and 0.01 ppm, and larval survival was monitored to determine the appropriate sub-lethal dose. Concentrations with survival > 50% (0.00001 and 0.0001 ppm) were selected and used as the sub-lethal doses. The fecundity, fertility, and susceptibility to ivermectin of adults emerging after larval exposure to the sub-lethal doses were examined.
Results
Overall, exposure of An. gambiae s.s. aquatic stages to ivermectin caused a dose-dependent reduction in larval survival irrespective of the stage at which the larvae were exposed. Exposure to ivermectin in the larval stage did not have an effect on either the number of eggs laid or the hatch rate. However, exposure of first/second-instar larvae to 0.0001 ppm and third/fourth-instar larvae to 0.001 ppm of ivermectin reduced the time taken to oviposition. Additionally, exposure to ivermectin in the larval stage did not affect susceptibility of the emerging adults to the drug.
Conclusions
This study shows that contamination of larval habitats with ivermectin affects An. gambiae s.s. larval survival and could potentially have an impact on public health. However, there are no carry-over effects on the fecundity, fertility, and susceptibility of the emerging adults to ivermectin. In addition, this study shows that environmental exposure to ivermectin in the larval habitats is unlikely to compromise the efficacy of ivermectin in the emerging adults.
Graphical Abstract
... However, other active ingredients have recently been repurposed, including neonicotinoids and pyrroles [2]. Resistance to commonly used insecticides has been reported in malaria vectors in several sub-Saharan African countries [3][4][5][6][7][8][9]. ...
... Furthermore, the uncontrolled and improper use of agrochemicals can lead to the development of insecticide resistance in non-target insects, including malaria vectors breeding in agricultural areas, since the compounds used to control crop pests often have the same active ingredients and molecular targets as those used in public health. [5]. Therefore, farming irrigation greatly increases the risk of malaria for nearby communities as well as the development of insecticide resistance by pesticides intended to control crop pests [33][34][35]. ...
Background
Insecticide-based malaria vector control is increasingly undermined due to the development of insecticide resistance in mosquitoes. Insecticide resistance may partially be related to the use of pesticides in agriculture, while the level and mechanisms of resistance might differ between agricultural practices. The current study aimed to assess whether phenotypic insecticide resistance and associated molecular resistance mechanisms in Anopheles gambiae sensu lato differ between agricultural practices.
Methods
We collected An. gambiae s.l. larvae in six sites with three different agricultural practices, including rice, vegetable and cocoa cultivation. We then exposed the emerging adult females to discriminating concentrations of bendiocarb (0.1%), deltamethrin (0.05%), DDT (4%) and malathion (5%) using the standard World Health Organization insecticide susceptibility test. To investigate underlying molecular mechanisms of resistance, we used multiplex TaqMan qPCR assays. We determined the frequency of target-site mutations, including Vgsc-L995F/S and Vgsc-N1570Y, and Ace1-G280S. In addition, we measured the expression levels of genes previously associated with insecticide resistance in An. gambiae s.l., including the cytochrome P450-dependent monooxygenases CYP4G16, CYP6M2, CYP6P1, CYP6P3, CYP6P4, CYP6Z1 and CYP9K1, and the glutathione S-transferase GSTe2.
Results
The An. gambiae s.l. populations from all six agricultural sites were resistant to bendiocarb, deltamethrin and DDT, while the populations from the two vegetable cultivation sites were additionally resistant to malathion. Most tested mosquitoes carried at least one mutant Vgsc-L995F allele that is associated with pyrethroid and DDT resistance. In the cocoa cultivation sites, we observed the highest 995F frequencies (80–87%), including a majority of homozygous mutants and several in co-occurrence with the Vgsc-N1570Y mutation. We detected the Ace1 mutation most frequently in vegetable-growing sites (51–60%), at a moderate frequency in rice (20–22%) and rarely in cocoa-growing sites (3–4%). In contrast, CYP6M2, CYP6P3, CYP6P4, CYP6Z1 and CYP9K1, previously associated with metabolic insecticide resistance, showed the highest expression levels in the populations from rice-growing sites compared to the susceptible Kisumu reference strain.
Conclusion
In our study, we observed intriguing associations between the type of agricultural practices and certain insecticide resistance profiles in the malaria vector An. gambiae s.l. which might arise from the use of pesticides deployed for protecting crops.
Graphical Abstract
... The role of agricultural pesticides spraying in the development of resistance to insecticides used in malaria mosquito control has been widely documented [24][25][26][27][28][29][30][31] . It has recently been demonstrated that An. gambiae larvae collected from farming areas where formulations of acetamiprid and imidacloprid, two neonicotinoids, are intensively used for crop protection can grow and emerge in water containing doses of neonicotinoids that were lethal to susceptible strains 32 . ...
Chronic exposure of mosquito larvae to pesticide residues in agricultural areas is often associated with evolution of resistance to insecticides used for vector control. This presents a concern for the efficacy of clothianidin, an agricultural neonicotinoid qualified for Indoor Residual Spraying (IRS). Using standard bioassays, we tested if reduced susceptibility to clothianidin affects the efficacy of SumiShield® 50WG, one of the two newly approved formulations, which contains 50% clothianidin. We simultaneously monitored susceptibility to clothianidin and to SumiShield® 50WG, testing adults of Anopheles gambiae , An. coluzzii and Culex sp collected from urban, suburban and agricultural areas of Yaoundé. We found that the level of susceptibility to the active ingredient predicted the efficacy of SumiShield® 50WG. This formulation was very potent against populations that achieved 100% mortality within 72 h of exposure to a discriminating dose of clothianidin. By contrast, mortality leveled off at 75.4 ± 3.5% within 7 days of exposure to SumiShield® 50WG in An. gambiae adults collected from a farm where spraying of acetamiprid and imidacloprid is driving cross-resistance to clothianidin. These findings indicate that more potent formulations of clothianidin or different insecticides should be prioritized in areas where resistance is emerging.
... Malheureusement, l'émergence de la résistance aux pyréthrinoïdes chez les vecteurs du paludisme constitue une menace à l'encontre des stratégies de lutte utilisées par les Programmes Nationaux de Lutte contre le Paludisme (Ranson et Lissenden, 2016). En effet, des études antérieures avaient rapporté la résistance des vecteurs du paludisme aux insecticides chimiques (Chandre et al., 1999;Diabate et al., 2002;Namountougou et al., 2019). Aussi, plusieurs études ont signalé une résistance aux insecticides chez les vecteurs de la dengue dans le monde entier, notamment en Inde (Bharati & Saha, 2018), au Brésil (de Araújo et al., 2019), en Malaisie (Ishak et al., 2017), au Laos (Marcombe et al., 2019), au Myanmar (Kawada et al., 2014), en Afrique (Kamgang et al., 2011;Kawada et al., 2016), et particulièrement au Burkina Faso Sombié et al., 2019;Namountougou et al., 2020, Toé et al., 2022. ...
Le paludisme et la dengue sont les deux principales maladies vectorielles transmises respectivement par les genres Anopheles et Aedes. La lutte antivectorielle (LAV) est basée essentiellement sur l'utilisation d’insecticides de synthèse à partir de produits chimiques. La prolifération des molécules insecticides et le développement de la résistance de ces vecteurs aux insecticides de synthèse suscitent un intérêt de rechercher des outils innovants comme ceux basés sur les produits naturels extraits de plantes à propriété insecticide, comme les huiles essentielles (HE) qui peuvent constituer une alternative aux insecticides chimiques. L’objectif de cette thèse est d’étudier les activités larvicides, adulticides et répulsives-irritantes des HE de Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora et Ocimum americanum seules et en combinaison sur les populations de Ae. aegypti de Bobo-Dioulasso et An. gambiae de la Vallée du Kou (VK) dans l’Ouest du Burkina Faso selon les protocoles de l’OMS (2017). Les composés chimiques des HE extraites de ces 5 plantes ont été identifiés par GC-MS. L’HE de L. multiflora dont les composés majeurs sont le ß-caryophyllène, le p-cymène, l'acétate de thymol et le 1,8 cinéol est la plus toxique sur les larves de Ae. aegypti et de An. gambiae avec une activité proche du pyriproxyfène, contrôle positif sur les larves. La population de An. gambiae a été plus sensible aux HE testées que celle de Ae. aegypti. Concernant les tests adulticides, l’HE de L. multiflora et les combinaisons constituées de C. nardus : 80% et O. americanum : 20% (C8) et C. nardus : 90% et O. americanum : 10% (C9) sur An. gambiae et C. nardus : 20% et O. americanum : 80% (C2), C8 et C9 sur Ae. aegypti, ont été les plus toxiques. Aussi, les combinaisons C9 et C8 ont donné des effets synergiques respectivement sur An. gambiae de VK et Ae. aegypti de Bobo-Dioulasso. En plus, les combinaisons C9 et C2 ont donné des effets additionnels sur Ae. aegypti de Bobo-Dioulasso.
Les HE de C. citratus, C. nardus et E. camaldulensis ont produit des effets répulsifs irritants de contact très proches de ceux du DEET sur An. gambiae et Ae. aegypti.
L’HE de L. multiflora et les combinaisons C8 et C9 de C. nardus et de O. americanum pourraient être utilisées comme bio insecticides alternatifs aux insecticides chimiques dans la LAV. Les données de cette thèse sont précieuses et contribueront sans doute à l’amélioration du dispositif de lutte antivectorielle contre ces espèces de moustiques au Burkina Faso.
... Malheureusement, l'émergence de la résistance aux pyréthrinoïdes chez les vecteurs du paludisme constitue une menace à l'encontre des stratégies de lutte utilisées par les Programmes Nationaux de Lutte contre le Paludisme (Ranson et Lissenden, 2016). En effet, des études antérieures avaient rapporté la résistance des vecteurs du paludisme aux insecticides chimiques (Chandre et al., 1999;Diabate et al., 2002;Namountougou et al., 2019). Aussi, plusieurs études ont signalé une résistance aux insecticides chez les vecteurs de la dengue dans le monde entier, notamment en Inde (Bharati & Saha, 2018), au Brésil (de Araújo et al., 2019), en Malaisie (Ishak et al., 2017), au Laos (Marcombe et al., 2019), au Myanmar (Kawada et al., 2014), en Afrique (Kamgang et al., 2011;Kawada et al., 2016), et particulièrement au Burkina Faso Sombié et al., 2019;Namountougou et al., 2020, Toé et al., 2022. ...
Le paludisme et la dengue sont les deux principales maladies vectorielles transmises respectivement par les genres Anopheles et Aedes. La lutte antivectorielle (LAV) est basée essentiellement sur l'utilisation d’insecticides de synthèse à partir de produits chimiques. La prolifération des molécules insecticides et le développement de la résistance de ces vecteurs aux insecticides de synthèse suscitent un intérêt de rechercher des outils innovants comme ceux basés sur les produits naturels extraits de plantes à propriété insecticide, comme les huiles essentielles (HE) qui peuvent constituer une alternative aux insecticides chimiques. L’objectif de cette thèse est d’étudier les activités larvicides, adulticides et répulsives-irritantes des HE de Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora et Ocimum americanum seules et en combinaison sur les populations de Ae. aegypti de Bobo-Dioulasso et An. gambiae de la Vallée du Kou (VK) dans l’Ouest du Burkina Faso selon les protocoles de l’OMS (2017). Les composés chimiques des HE extraites de ces 5 plantes ont été identifiés par GC-MS. L’HE de L. multiflora dont les composés majeurs sont le ß-caryophyllène, le p-cymène, l'acétate de thymol et le 1,8 cinéol est la plus toxique sur les larves de Ae. aegypti et de An. gambiae avec une activité proche du pyriproxyfène, contrôle positif sur les larves. La population de An. gambiae a été plus sensible aux HE testées que celle de Ae. aegypti. Concernant les tests adulticides, l’HE de L. multiflora et les combinaisons constituées de C. nardus : 80% et O. americanum : 20% (C8) et C. nardus : 90% et O. americanum : 10% (C9) sur An. gambiae et C. nardus : 20% et O. americanum : 80% (C2), C8 et C9 sur Ae. aegypti, ont été les plus toxiques. Aussi, les combinaisons C9 et C8 ont donné des effets synergiques respectivement sur An. gambiae de VK et Ae. aegypti de Bobo-Dioulasso. En plus, les combinaisons C9 et C2 ont donné des effets additionnels sur Ae. aegypti de Bobo-Dioulasso.
Les HE de C. citratus, C. nardus et E. camaldulensis ont produit des effets répulsifs irritants de contact très proches de ceux du DEET sur An. gambiae et Ae. aegypti.
L’HE de L. multiflora et les combinaisons C8 et C9 de C. nardus et de O. americanum pourraient être utilisées comme bio insecticides alternatifs aux insecticides chimiques dans la LAV. Les données de cette thèse sont précieuses et contribueront sans doute à l’amélioration du dispositif de lutte antivectorielle contre ces espèces de moustiques au Burkina Faso.
Mots clés : Aedes aegypti, Anopheles gambiae, Huile essentielle, combinaison, Lutte antivectorielle
Abstract
Malaria and dengue fever are the two main vector diseases transmitted by Anopheles gambiae and Aedes aegypti respectively. Vector Control is based mainly on the use of chemicals. Concern for environmental safety and the development of chemical resistance in these vectors has led to an interest in investigating innovative tools, including plant-based insecticides as alternatives to chemical insecticides.
The thesis aimed at evaluating larvicides, adulticides and repellent-irritant of 5 essential oils namely Cymbopogon citratus, Cymbopogon nardus, Eucalyptus camaldulensis, Lippia multiflora and Ocimum americanum alone or in combinations on populations of Bobo-Dioulasso Ae. aegypti and “Vallée du Kou” An. gambiae collected in western Burkina Faso according to WHO protocols. As results, the EO of L. multiflora whose major compounds were ß-caryophyllene, p-cymene, thymol acetate and 1,8-cineole were more toxic against larvae of Ae. aegypti and An. gambiae and their activity was close to Pyriproxyfen (The positive control). In terms of adulticides tests, L. multiflora EO and combinations of C8 (C. nardus: 80% and O. americanum: 20%) and C9 (C. nardus: 90% and O. americanum: 10%) on An. gambiae and C2 (C. nardus: 20% and O. americanum: 80%), C8 and C9 on Ae. aegypti were the most toxic. The combinations C9 and C8 gave synergistic effects on An. gambiae from the “Vallée du Kou” and Ae. aegypti from Bobo-Dioulasso respectively. The combinations C9 and C2 gave additional effects on Ae. aegypti from Bobo-Dioulasso. The EOs of C. citratus, C. nardus and E. camaldulensis produced contact irritant repellent effects very similar to those of DEET on An. gambiae. On Ae. aegypti, the EOs of C. citratus, O. americanum and E. camaldulensis were very close to DEET.L. multiflora and combinations of C8 and C9 of C. nardus and O. americanum could be used as alternative insecticides to chemical insecticides in vector control. The data of this thesis are valuable and will undoubtedly contribute to the improvement of the vector control strategies against these mosquitos’ species in Burkina Faso.
... An. arabiensis seems to be better adapted to such urban environments con rming its predominance in large cities of West Africa such as Dakar and Nouakchott [9,10] [20] showed that the kdr-w mutation was widespread in six urban areas in Burkina Faso with frequencies ranging from 0.66 to 0.98. Several studies have demonstrated the impact of agricultural practices on the selection of resistance to insecticides in Burkina Faso [51,52]; and in other African countries [12,[53][54][55]. To this source, could be added the use of pyrethroids in public health, particularly the use of LLINs which would play a role in the intensi cation of resistance to pyrethroids [56, 57] but unfortunately remains poorly investigated. ...
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 <30%), but were fully susceptible to bendiocarb, fenitrothion, and malathion. High frequencies of pyrethroid resistance-associated 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.
... gambiae is observed toward the end of the rainy season (frequencies uctuating between ve and 20%). Both species are highly resistant to pyrethroids and DDT (kdr frequency (0.8-0.95) [9,[37][38][39]. ...
... The kdr L1014F mutation conferring resistance to pyrethroids and to DDT was found in the samples analysed to be very high (~ 0.9) when the study was carried out. This result is consistent with previous studies reporting a high level of resistance in mosquito populations due to the extensive use of pesticides in rice and cotton elds in the village [37,55,56]. In this study, environmental factors such as rainfall, humidity, and temperature had a great impact on mosquito densities. ...
Background
There is a great need to find new effective tools to prevent mosquitoes from biting humans. As part of this search, the Lehmann Funnel Entry Trap, a window screen, was tested and has proven to be effective in mosquito density reduction in low and high vector density settings. Here we aimed to assess whether a large-scale deployment of pyriproxyfen-treated traps can control malaria mosquito populations and how well the traps were accepted at community level.
Method
Overall, 1,313 traps impregnated with Pyriproxyfen (PPF) were deployed. Of these, 12 traps in 12 houses were randomly selected across the intervention village, Vallée du Kou 3 (VK3), for indoor mosquito density assessment compared to houses without traps in the control village, Vallée du Kou 5 (VK5). Traps were placed in the windows, while doors were blocked with curtains. From July until October 2015, for nine days per month, mosquitoes were collected from the traps and matching houses in VK3, and in houses only in VK5. Anopheles coluzzii collected from the field as adults and as larvae reared through to adults and An. gambiae were used or released into traps to assess the bio-efficacy effect of PPF in VK3 against control mosquitoes from VK5. Then, mosquitoes that were in contact with the PPF trap netting were allowed to oviposit in the laboratory for fecundity and egg fertility reduction evaluation as compared to a control. The mosquitoes collected as part of the monthly programme were morphologically identified, counted, and preserved in 80% ethanol vials for subsequent analyses, including resistance genes and female mosquito age structure. The impact of the trap on mosquito density at community level was assessed by performing a pyrethrum spray catch (PSC). The integrity of net fabric as well as some sociological points of view on the trap’s efficacy and design were then reported.
Results
Overall mosquito density was reduced by ~ 90% in all houses equipped with traps in VK3. At the community level, while mosquito density before intervention was 33% higher in VK3 than in VK5, it was 47% higher in VK5 after the intervention. Old female mosquito numbers increased in VK5 by 12% in October but not in VK3, indicating that the traps were cumulatively killing older females. The additional effect of PPF was to limit egg-laying, with a smaller number of eggs counted, and with a lower hatching rate than in VK5. Mosquitoes were highly resistant to pyrethroids with a ~ 0.9 frequency of the kdr mutation. The trap was well accepted by the communities as most of the interviewees in VK3 found the traps reduced mosquito bites with peaceful sleep. They hoped to keep the traps in place beyond the study period.
Conclusion
The Lehmann Funnel Entry Trap has real potential to control malaria mosquito populations and can be widely used to sustain the global effort of malaria elimination.
