[Susceptibility status of Anopheles gambiae s.s. and An. coluzzii to Organophosphates and Carbamates in the Agricultural Exploitation Zones of oil Palm at Mouila, Gabon]. / Susceptibilité d'Anopheles gambiae s.s. et An. coluzzii aux organophosphorés et aux carbamates en zones d'exploitation industrielle de palmiers à huile à Mouila, Gabon.

This study was conducted during the rainy season of 2017 in the agricultural areas at Mouila, with the aim to assess the determination of susceptibility of Anopheles gambiae complex to insecticides and the detection of Ace 1R mutation. Mosquito larvae were collected by using the dipping method and nursed to adult stage. The susceptibility of adult Anopheles gambiae s.l. populations to organophosphates and carbamates was assessed using the standard WHO susceptibility test protocol. The tested mosquitoes species were identified by PCR. These tested mosquitoes were used to search for the Ace 1R mutation. The insecticides used were pirimiphos-methyl 0.25% and 1.25%, fenitrothion 1%, malathion 5%, propoxur 0.1%, bendiocarb 0.1%, 0.5% and 1%. In the prospected areas, An. gambiae s.l. included An. gambiae s.s. and An. coluzzii sympatric in their larval habitats. However, An. gambiae s.s. was predominant in all studied areas (99.1%) comparatively to An. coluzzii Moreover, the susceptibility tests of Anopheles to organophosphates and carbamates revealed mortality rates of 100% regardless of the origin of the mosquitoes. PCR diagnosis of Ace 1R mutation showed that none tested mosquito (An. gambiae s.s. and An. coluzzii) from prospected areas harbored the Ace 1R gene in all prospected areas. The lack of Ace 1R mutation in An. gambiae s.l. reveals the current effectiveness of organophosphates and carbamates for the control of these mosquitoes. Bboth these classes of insecticides could be used for the anopheline populations control in the agricultural spaces at Mouila.

Cette étude a été menée en 2017 pendant la saison des pluies dans les zones d'exploitations agricoles à Mouila, afin de déterminer le statut de sensibilité des membres du complexe Anopheles gambiae aux insecticides et de rechercher la présence de la mutation Ace 1R. Les moustiques ont été collectés au stade larvaire par la méthode du « dipping ¼, puis élevés jusqu'au stade adulte. La susceptibilité des adultes d'An. gambiae s.l. aux organophosphorés et aux carbamates a été évaluée par la méthode standard de l'OMS concernant les tests de sensibilité aux insecticides. Les classes d'insecticides testées étaient les organophosphorés (pirimiphos-méthyl 0,25 % et 1,25 %, fénitrothion 1 %, malathion 5 %) et les carbamates (propoxur 0,1 %, bendiocarb 0,1 %, 0,5 % et 1 %). Les moustiques testés ont été identifiés par PCR. Les anophèles issus des tests ont été utilisés pour la recherche de la mutation Ace 1R par PCR. Dans les sites d'étude, Anopheles gambiae s.l. était composé d'An. gambiae s.s. et An. coluzzii vivant en sympatrie dans leurs habitats larvaires, avec une prédominance d'An. gambiae s.s. (99,1 %) sur An. coluzzii. Les tests de sensibilité des anophèles aux organophosphorés et aux carbamates ont révélé des taux de mortalité de 100 % quelle que soit l'origine des anophèles. La PCR diagnostique de la mutation Ace 1R a montré qu'aucun moustique issu des tests de sensibilité n'était porteur de gènes de résistance Ace 1R. L'absence de mutation Ace 1R chez An. gambiae s.l. révèle l'efficacité actuelle des carbamates et des organophosphorés dans la lutte contre ces moustiques. Ces familles d'insecticides pourraient être utilisées pour la lutte contre les anophèles dans les espaces agricoles de Mouila.

Insecticide resistance in the Anopheles gambiae complex in Benin: a nationwide survey.

Benin has embraced World Health Organization-recommended preventive strategies to control malaria. Its National Malaria Control Programme is implementing and/or coordinating various actions and conducting evaluation trials of mosquito control strategies. Mosquito control is based on the use of insecticide-treated nets and indoor residual spraying, but the efficacy of these strategies to control malaria vectors is endangered by insecticide resistance. Here, we present the results of a nationwide survey on the status of insecticide susceptibility and resistance in Anopheles gambiae s.l. (Diptera: Culicidae) carried out in Benin in 2006-2007 (i.e. before extensive vector control was undertaken). Overall, our study showed that the S molecular form of An. gambiae s.s. predominates and is widely distributed across the country, whereas the frequency of the M form shows a strong decline with increasing latitude. Susceptibility to DDT, permethrin, carbosulfan and chlorpyrifos-methyl was assessed; individual mosquitoes were identified for species and molecular forms, and genotyped for the kdr and ace-1 loci. Full susceptibility to chlorpyrifos-methyl was recorded and very few samples displayed resistance to carbosulfan. High resistance levels to permethrin were detected in most samples and almost all samples displayed resistance to DDT. The kdr-Leu-Phe mutation was present in all localities and in both molecular forms of An. gambiae s.s. Furthermore, the ace-1(R) mutation was predominant in the S form, but absent from the M form. By contrast, no target modification was observed in Anopheles arabiensis. Resistance in the An. gambiae S molecular form in this study seemed to be associated with agricultural practices. Our study showed important geographic variations which must be taken into account in the vector control strategies that will be applied in different regions of Benin. It also emphasizes the need to regularly monitor insecticide resistance across the country and to adapt measures to manage resistance.

[Vector control methods against malaria and vector resistance to insecticides in Africa]. / Lutte antivectorielle contre le paludisme et resistance des vecteurs aux insecticides en Afrique.

Vector control methods against malaria must be adapted to the targeted vectors. Control methods against malaria currently depend on deploying insecticide-treated nets, indoor spraying of remanent insecticides and, to a lesser extent, eliminating larval breeding sites. The remanence of the insecticidal effect and efficacy of the vector control must be evaluated. Vector resistance to insecticides is one of the main limitations for use.

Distribution of insensitive acetylcholinesterase (ace-1R) in Anopheles gambiae s.l. populations from Burkina Faso (West Africa).

OBJECTIVE: To investigate through countrywide sampling at 20 localities across the three different agro-climatic zones of Burkina Faso, the distribution of the acetylcholinesterase insensitive mutation ace-1(R), which confers resistance to organophosphates (OP) and carbamates (CM) insecticides in An. gambiae s.l. METHODS: Adult mosquitoes were collected by indoor aerosol spraying from August to October 2006. Specimens were identified to species by polymerase chain reaction (PCR) assay and characterized for the ace-1(R) mutation using a PCR-restriction fragment length polymorphism diagnostic. RESULTS: Collected mosquitoes were a mixture of An. gambiae s.s. and An. arabiensis across the Sudan (98.3%vs. 1.7%), Sudan-sahelian (78.6%vs. 21.4%) and the Sahel (91.5%vs. 8.5%) ecotypes. The An. gambiae S-form predominated in the Sudan sites from the West (69%vs. 31% for the M form) but was not found in the Sahel (100% M form). The ace-1(R) mutation was dispersed throughout the Sudan and Sudan-sahelian localities at moderate frequency (<50%) but was absent in the Sahel. It was far more prevalent in S form than M form mosquitoes (0.32 for the S form vs. 0.036 for the M form). No An. arabiensis was detected carrying the mutation. The geographic distribution of ace-1(R) in the Sudan and Sudan-sahelian correlated with the cotton growing areas dispersed throughout the two climatic zones. CONCLUSIONS: These results have special significance as OP and CM insecticides have been proposed as alternatives or additions to pyrethroids which are currently used exclusively in many vector control programmes.

Lutte antivectorielle contre le paludisme et resistance des vecteurs aux insecticides en Afrique

La lutte antivectorielle contre le paludisme doit etre adaptee aux vecteurs cibles. Elle repose actuellement sur les moustiquaires impregnees d'insecticide; sur l'aspersion intradomiciliaire d'insecticides et; dans une moindre mesure; sur la lutte contre les gites larvaires. La remanence de l'effet insecticide et l'efficacite de la lutte doivent etre verifiees. La resistance des vecteurs aux insecticides est une des principales limites a leur utilisation

Presence of insensitive acetylcholinesterase in wild populations of Culex pipiens quinquefasciatus from Benin.

Resistance to organophosphates and carbamates was investigated in three samples of Culex pipiens quinquefasciatus Say, from Cotonou and Parakou in the Republic of Benin. Each population of larvae was selected with propoxur to eliminate susceptible individuals and more easily analyse resistant mosquitoes if the resistance allele is present in the field sample. The mass-selection showed that there are resistant mosquitoes in natural populations of C. p. quinquefasciatus in Benin and that nowadays they are still at a low frequency. The result of the PCR-based assay revealed the presence of the G119S mutation in all the C. p. quinquefasciatus mosquitoes that survived exposure to mass-selection. This mutation is the same than reported in a large range of insects, including Anopheles gambiae. Thus, the G119S mutation is spreading in natural populations of C. p. quinquefasciatus in Africa. Therefore, good mosquito control strategies and agricultural use of insecticides are critical, and should be carefully applied to limit the spread of this resistance gene.

Characterization of insensitive acetylcholinesterase (ace-1R) in Anopheles gambiae (Diptera: Culicidae): resistance levels and dominance.

Characterization of insecticide resistance provides data on the evolutionary processes involved in the adaptation of insects to environmental changes. Studying the dominance status and resistance level represents a great interest, in terms of understanding resistance evolution in the field to eventually adapt vector control. Resistance and dominance levels conferred by the G119S mutation of acetylcholinesterase (ace-1R) of the mosquito Anopheles gambiae s.s. (Diptera: Culicidae) were studied for various insecticides belonging to different classes, using strains sharing the same genetic background. Our survey shows that the homozygote resistant strain AcerKis displayed a very high resistance level to various carbamates (range 3,000- to 5,000-fold) compared with that of various organophosphates (range 12- to 30-fold). Furthermore, the dominance status varied between semi-recessivity with fenitrothion and chlorpyrifos methyl insecticides to semidominance with temephos, carbosulfan, and propoxur. These results indicate that this resistance mechanism could spread rapidly in the field and then compromise the use of organophosphate and carbamate compounds in public health. This study underlines the necessity to monitor the ace-1R mutation in natural populations before planning and implementing malaria control programs based on the use of these insecticides.

Multiple insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus from Benin, West Africa.

Because free-insecticide treated net distribution is planned in Benin (West Africa) during the next few years, we investigated the type, frequency and distribution of insecticide resistance mechanisms in Anopheles gambiae and Culex quinquefasciatus mosquitoes in four localities selected on the basis of contrasting agricultural practices, use of insecticides and environment. Bioassays with WHO diagnostic test kits were carried out using pyrethroid, carbamate, organophosphate and organochlorine insecticides. An. gambiae mosquitoes were identified to species and to M or S molecular forms using PCR techniques. Molecular and biochemical assays were carried out to identify kdr and Ace.1 mutations in individual mosquitoes and to detect any increase in the activity of enzymes typically involved in insecticide metabolism (oxidase, esterase and glutathion-S-transférases). WHO diagnostic tests showed high frequency of resistance in An. gambiae and Cx. quinquefasciatus to permethrin and DDT in three areas. This was consistent with the presence of target site insensitivity due to kdr mutation and to increased metabolism through enzymatic activity. Kdr was expressed in both M and S forms. However, less than 1% of An. gambiae or Cx. quiqnuefasciatus showed the presence of the Ace.1(R) mutation. Carbamate/OP resistance was present at higher frequency in Culex than in An. gambiae. Dieldrin resistance was present in both species at all four localities. A higher frequency of pyrethroid-resistance was found in An. gambiae mosquitoes collected in urban areas compared to those collected in rice growing areas. The expansion of vegetable growing within urban areas probably contributed to selection pressure on mosquitoes. The detection of multiple resistance mechanisms in both An. gambiae and Cx. quinquefasciatus in Benin may represent a threat for the efficacy of ITNs and other forms of vector control such as indoor residual spraying in the future.