Malaria vectors in the Republic of Benin: Distribution of species and molecular forms of the Anopheles gambiae complex

Djogbénou, Luc; Pasteur, Nicole; Bio-Bangana, Sahabi; Baldet, Thierry; Irish, Seth R.; Akogbéto, Martin; Weill, Mylène; Chandre, Fabrice

doi:10.1016/j.actatropica.2010.02.001

Cited by 48 publications

(48 citation statements)

References 39 publications

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“…More recently, Nwakanma et al [12] reported high frequencies (5–42%) of M/S hybrid forms at 12 sites in the four contiguous countries of The Gambia, Senegal, Guinea-Bissau and Republic of Guinea. However, in other coastal areas of Africa the observed frequency of M/S hybrids did not exceed 0.2% [7], [13] and so it is unknown whether this phenomenon is specific to the westernmost areas of West Africa, including Senegambia. We undertook a longitudinal study within two transects under differential insecticide pressure in inland areas in south-eastern Senegal to (i) study the distribution patterns of the M and S molecular forms, (ii) estimate the frequencies of M/S hybrids in these sites, and (iii) use our observations to determine the extent of ongoing speciation in these inland areas.…”

Section: Introductionmentioning

confidence: 91%

“…gambiae species range, whereas the M form is restricted to western parts of Africa, where it is common. Hybridization between them is rare in most areas of sympatry [6]; extensive studies conducted throughout areas of sympatric distribution showed variable but restricted gene flow between the M and S forms [2], [6], [7]. This has resulted in the two forms being recognized as good species named An.…”

Section: Introductionmentioning

confidence: 99%

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Reproductive Isolation among Sympatric Molecular Forms of An. gambiae from Inland Areas of South-Eastern Senegal

et al. 2014

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The Anopheles gambiae species complex includes at least seven morphologically indistinguishable species, one of which, Anopheles gambiae sensu stricto, is the primary mosquito vector responsible for the transmission of malaria across sub-Saharan Africa. Sympatric ecological diversification of An. gambiae s.s. is in progress within this complex, leading to the emergence of at least two incipient species (the M and S molecular forms now recognized as good species and named An. coluzzii and An. gambiae respectively) that show heterogeneous levels of divergence in most parts of Africa. However, this process seems to have broken down in coastal areas of West Africa at the extreme edge of the distribution. We undertook a longitudinal study to describe An. gambiae s.s. populations collected from two inland transects with different ecological characteristics in south-eastern Senegal. Analysis of samples collected from 20 sites across these two transects showed the M and S molecular forms coexisted at almost all sampled sites. Overall, similar hybridization rates (2.16% and 1.86%) were recorded in the two transects; sites with relatively high frequencies of M/S hybrids (up to 7%) were clustered toward the north-western part of both transects, often near urban settings. Estimated inbreeding indices for this putative speciation event varied spatially (range: 0.52–1), with hybridization rates being generally lower than expected under panmictic conditions. Such observations suggest substantial reproductive isolation between the M and S molecular forms, and further support the ongoing process of speciation in these inland areas. According to a recent reclassification of the An. gambiae complex, the M and S molecular forms from this zone correspond to An. coluzzii and An. gambiae, respectively. There is considerable evidence that these molecular forms differ in their behavioural and ecological characteristics. Detailed study of these characteristics will allow the development and implementation of better insect control strategies for combating malaria.

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Reproductive Isolation among Sympatric Molecular Forms of An. gambiae from Inland Areas of South-Eastern Senegal

et al. 2014

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“…The lowest frequency of Ace-1 R was recorded during the same study and may be a sign of encouragement to use carbamates or organophosphates as alternative insecticides to pyrethroids for IRS in Benin. However, Aïkpon and others [19] have recently demonstrated a decrease of An. gambiae susceptibility to bendiocarb after the IRS implementation using bendiocarb in Atacora region in Benin.…”

Section: Introductionmentioning

confidence: 99%

Good performances but short lasting efficacy of Actellic 50 EC Indoor Residual Spraying (IRS) on malaria transmission in Benin, West Africa

Aïkpon

Sezonlin

Tokponon³

et al. 2014

Parasit Vectors

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BackgroundThe National Malaria Control Program (NMCP) has been using pirimiphos methyl for the first time for indoor residual spraying (IRS) in Benin. The first round was a success with a significant decrease of entomological indicators of malaria transmission in the treated districts. We present the results of the entomological impact on malaria transmission. Entomologic parameters in the control area were compared with those in intervention sites.MethodsMosquito collections were carried out in three districts in the Atacora-Dongo region of which two were treated with pirimiphos methyl (Actellic 50EC) (Tanguiéta and Kouandé) and the untreated (Copargo) served as control. Anopheles gambiae s.l. populations were sampled monthly by human landing catch. In addition, window exit traps and pyrethrum spray catches were performed to assess exophagic behavior of Anopheles vectors. In the three districts, mosquito collections were organized to follow the impact of pirimiphos methyl IRS on malaria transmission and possible changes in the behavior of mosquitoes. The residual activity of pirimiphos methyl in the treated walls was also assessed using WHO bioassay test.ResultsA significant reduction (94.25%) in human biting rate was recorded in treated districts where an inhabitant received less than 1 bite of An. gambiae per night. During this same time, the entomological inoculation rate (EIR) dramatically declined in the treated area (99.24% reduction). We also noted a significant reduction in longevity of the vectors and an increase in exophily induced by pirimiphos methyl on An. gambiae. However, no significant impact was found on the blood feeding rate. Otherwise, the low residual activity of Actellic 50 EC, which is three months, is a disadvantage.ConclusionPirimiphos methyl was found to be effective for IRS in Benin. However, because of the low persistence of Actellic 50EC used in this study on the treated walls, the recourse to another more residual formulation of pirimiphos methyl is required.

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“…Previous studies on the effects of the 2L a inversion on stress resistance have used laboratory strains of the M form [27]–[29]. However, because of their discontinuous geographical distribution [20], [36], [37], natural populations of the M form are almost fixed for either the inverted or the standard 2L a arrangement. As a result, studies on populations of the M form may fail to disentangle the effects of 2L a status and other geographically-dependent genetic differences.…”

Section: Introductionmentioning

confidence: 99%

Adaptation to Aridity in the Malaria Mosquito Anopheles gambiae: Chromosomal Inversion Polymorphism and Body Size Influence Resistance to Desiccation

et al. 2012

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Chromosomal inversions are thought to confer a selective advantage in alternative habitats by protecting co-adapted alleles from recombination. The frequencies of two inversions (2La and 2Rb) of the afro-tropical malaria mosquito Anopheles gambiae change gradually along geographical clines, increasing in frequency with degree of aridity. Such clines can result from gene flow and local selection acting upon alternative karyotypes along the cline, suggesting that these inversions may be associated with tolerance to xeric conditions. Since water loss represents a major challenge in xeric habitats, it can be supposed that genes inside these inversions are involved in water homeostasis. To test this hypothesis, we compared the desiccation resistance of alternative karyotypes from a colonised 2Rb/2La polymorphic population of A. gambiae from Cameroon. The strain included only the molecular form S, one of the genetic units marking incipient speciation in this taxon. Day-old mosquitoes of both sexes were assayed individually for time to death in a dry environment and the karyotype of each was determined post-mortem using molecular diagnostic assays for each inversion. In agreement with expectations based on their eco-geographical distribution, we found that 2La homokaryotypes survived significantly longer (1.3 hours) than the other karyotypes. However, there was weak support for the effect of 2Rb on desiccation resistance. Larger mosquitoes survived longer than smaller ones. Median survival of females was greater than males, but the effect of sex on desiccation resistance was weakly supported, indicating that differential survival was correlated to differences between sexes in average size. We found weak evidence for a heterotic effect of 2La karyotype on size in females. These results support the notion that genes located inside the 2La inversion are involved in water balance, contributing towards local adaptation of A. gambiae to xeric habitats, beyond the adaptive value conferred by a larger body size.

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Malaria vectors in the Republic of Benin: Distribution of species and molecular forms of the Anopheles gambiae complex

Cited by 48 publications

References 39 publications

Reproductive Isolation among Sympatric Molecular Forms of An. gambiae from Inland Areas of South-Eastern Senegal

Reproductive Isolation among Sympatric Molecular Forms of An. gambiae from Inland Areas of South-Eastern Senegal

Good performances but short lasting efficacy of Actellic 50 EC Indoor Residual Spraying (IRS) on malaria transmission in Benin, West Africa

Adaptation to Aridity in the Malaria Mosquito Anopheles gambiae: Chromosomal Inversion Polymorphism and Body Size Influence Resistance to Desiccation

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