Boosting the sterile insect technique with pyriproxyfen increases tsetse flies Glossina palpalis gambiensis sterilization in controlled conditions.

Tsetse flies (Diptera: Glossinidae) are the main vectors of animal and human trypanosomoses in Africa. The Sterile Insect Technique (SIT) has proven effective in controlling tsetse flies when applied to isolated populations but necessitates the production of large numbers of sterile males. A new approach, called boosted SIT, combining SIT with the contamination of wild females by sterile males coated with biocides has been proposed for large-scale control of vector populations. The aim of the study was to evaluate this new approach using pyriproxyfen on the riverine species Glossina palpalis gambiensis (Vanderplank, 1949) in the laboratory. The contamination dose and persistence of pyriproxyfen on sterile males, the impact of pyriproxyfen on male survival, and the dynamics of pyriproxyfen transfer from a sterile male to a female during mating, as well as the impact of pyriproxyfen on pupal production and adult emergence, were evaluated in the laboratory. For this purpose, a method of treatment by impregnating sterile males with a powder containing 40% pyriproxyfen has been developed. The results showed that the pyriproxyfen has no impact on the survival of sterile males. Pyriproxyfen persisted on sterile males for up to 10 days at a dose of 100 ng per fly. In addition, the horizontal transfer of pyriproxyfen from a treated sterile male to a female during mating could be measured with an average of 50 ng of pyriproxyfen transferred. After contacts without mating, the average quantity transferred was more than 10 ng. Finally, the pyriproxyfen powder was very effective on G. p. gambiensis leading to 0% emergence of the pupae produced by contaminated females. These promising results must be confirmed in the field. A large-scale assessment of this boosted pyriproxyfen-based SIT approach will be carried out against tsetse flies in Senegal (West Africa).

[Late impact of lambdacyhalothrin-treated nets on kdr allelic frequency in Anopheles gambiae s.s. (Diptera: Culicidae) from northern Côte-d'Ivoire]. / Impact retardé des moustiquaires imprégnées de lambdacyhalothrine sur la fréquence de la mutation kdr chez Anopheles gambiae s.s. (Diptera : Culicidae) au nord de la Côte-d'Ivoire.

Nets treated with lambdacyhalothrin 15 mg a.i./m2 were distributed in four villages of Korhogo area in northern Côte-d'Ivoire, and four other villages without nets were followed as controls. Mosquitoes were collected every three months from June 1999 to August 2000 in the villages, and then tested to determine their genotypes for kdr mutation L1014F conferring cross-resistance to pyrethroids and DDT and for M and S molecular forms of Anopheles gambiae s.s. The frequencies of the resistant allele at kdr mutation L1014F locus were very high and they varied from 0.82 to 0.96. Before the trial, the genotypic frequencies of specimens at kdr locus did not show any significant difference. However, they significantly increased in mosquitoes from treated villages (0.94) compared to those from control villages (0.87) on month 14 (P = 0.013). No significant difference was observed between mosquitoes collected outside and inside the houses (P < 0.05). In contrary, a significant difference was observed before and after the trial between mosquitoes from villages with two cycles of rice cultivation per year and those from villages without rice cultivation (P = 0.008 and P = 0.012). Nine out of twelve populations of field mosquitoes showed Hardy-Weinberg disequilibrium at kdr locus (P < 0.05). The S and M molecular forms of An. gambiae s.s. were sympatric in Korhogo area and the S form represents 97%. No hybrid between M and S forms was observed. All individuals of the M form were homozygote susceptible at kdr locus.

The moth Hylesia metabus and French Guiana lepidopterism: centenary of a public health concern.

The females of the moths Hylesia metabus have their abdomens covered by urticating hairs looking like micro-arrows and causing a puriginous dermatitis to humans known as "papillonite" in French Guiana and also called yellowtail moth dermatitis or Caripito itch. The densities of the moths show great seasonal and annual variations depending on mechanisms mostly unknown. When H. metabus infestations occur, numerous cases of dermatologic manifestations are reported from people living near the mangrove swamps where the moths are developing. One hundred years after the first "papillonite" epidemic reported from French Guiana in 1912, the data presented herein summarize the actual state of knowledge on H. metabus biology and ecology and on the lepidopterism. Some recommendations are proposed for the surveillance and warning systems of H. metabus infestations and to avoid contact with the moths. Research priorities are suggested to improve the control against this problem emerging between nuisance and public health.

The combination of NPK fertilizer and deltamethrin insecticide favors the proliferation of pyrethroid-resistant Anopheles gambiae (Diptera: Culicidae).

In this laboratory study, we investigated how the biological cycle of Anopheles gambiae s.s. (VKPR strain) would be like when grew in an environment containing more or less plant matter (2.5 or 5 g/l) and fertilizer (8-12-8 or 17-23-17 mg/l). Half of the environments studied were not exposed to insecticide (control) whereas the other half was submitted to deltamethrin treatment at the concentration of 0.015 mg/l. The bioassays showed that 2.5 g/l of plant matter in water are not sufficient to feed the hundred larvae, each breeding site contains. Treating these breeding sites with deltamethrin reversed the situation as it decreased the competition for food resources and allowed the surviving larvae to share the small amount of food enabling them to pursue their development until adults. If the introduction of NPK in untreated sites has not improved the nutritive qualities of the water, in the treated sites it multiplied the number of emerging adults by 2.5. In the waters containing 5 g/l of plant matter, the larvae did not undergo feeding competition and the impact of insecticide followed of a more traditional selection scheme that expressed itself by a lower number of emerging adults. In these environments treated or nontreated where plant matter is abundant, adding NPK brings food supplement to the larvae therefore increases the survival rate of An. gambiae. To conclude, whether in habitats with little or much plant matter, NPK presence in water results in larger adults with generally, more soluble proteins.

Contribution of Anopheles funestus, An. gambiae and An. nili (Diptera: Culicidae) to the perennial malaria transmission in the southern and western forest areas of Côte d'Ivoire.

The involvement of members of the Anopheles gambiae complex Giles and An. funestus Giles and An. nili Theobald groups in the transmission of Plasmodium falciparum was recently investigated in the villages of Gbatta and Kpéhiri, which lie, respectively, in forest areas in the west and south of Côte d'Ivoire. Adult female mosquitoes were collected, using human landing catches, inside and outside dwellings. After identification and dissection, the heads and thoraces of all the anopheline mosquitoes were tested, in an ELISA, for circumsporozoite protein (CSP). All the female anopheline mosquitoes collected and identified to species using PCR were found to be An. gambiae s.s., An. nili s.s. or An. funestus s.s., with An. gambiae s.s. and An. funestus s.s. predominant in Gbatta but An. nili s.s. the most common species in Kpéhiri. In Gbatta, 3·1% of the female An. gambiae collected, 5·0% of the female An. funestus and 1·8% of the female An. nili were found CSP-positive. The corresponding values in Kpéhiri were even higher, at 5·9%, 6·2% and 2·4%, respectively. The estimated entomological inoculation rates (EIR) were very high: 302 infected bites (139 from An. gambiae, 146 from An. funestus and 17 from An. nili)/person-year in Gbatta and 484 infected bites (204 from An. gambiae, 70 from An. funestus and 210 from An. nili)/person-year in Kpéhiri. In Gbatta, An. gambiae s.s. was responsible for most of the rainy-season transmission while An. funestus became the main malaria vector in the dry seasons. In Kpéhiri, however, An. nili appeared to be the main vector throughout the year, with An. gambiae of secondary importance and An. funestus only becoming a significant vector during the rainy season. Although, in both study sites, intense transmission was therefore occurring and the same three species of anopheline mosquito were present, the relative importance of each mosquito species in the epidemiology of the human malaria at each site differed markedly.

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.

Review of Temephos Discriminating Concentration for Monitoring the Susceptibility of Anopheles labranchiae (Falleroni; 1926); Malaria Vector in Morocco

In Morocco; the resistance monitoring of Anopheles labranchiae larvae to temephos is done using discriminating concentration of 0.125?mg; which is half of the WHO recommended dose for Anopheles. However; this dosage seemed to be too high to allow an early detection of the resistance and its revision was found necessary. The present study was carried out during May-June 2008 and 2009 in nine provinces from the north-west of the country. The aim was to determine the lethal concentrations LC100 of temephos for the most susceptible populations and to define the discriminating dosage as the double of this value. The bioassays were conducted according to WHO standard operating protocol to establish the dose-mortality relationship and deduct the LC50 and LC95. The results of this study indicated that the LC100 obtained on the most susceptible populations was close to 0.05?mg/L. Therefore; the temephos discriminating dosage for susceptibility monitoring of An. labranchiae larvae in Morocco was set to be 0.1?mg

[Influence of plant matter and NPK fertilizer on the biology of Aedes aegypti (Diptera: Culicidae)]. / Influence des matières végétales et des engrais NPK sur la biologie de Aedes aegypti (Diptera : Culicidae).

In this laboratory study, we investigated the attractiveness of gravid Aedes aegypti females for aquatic habitats containing either NPK fertilizer or plant matter or a mixture of both. The development of larvae, adult emergence and weight of emerged adults were measured for each group and physicochemical analysis of water was made for the dosage of minerals and organic compounds. After 23 days experiment, NPK solution remained as attractive as the mixture of NPK + plant matter but did not ensure suitable development of larvae. The plant matter infusion showed less attractiveness for laying eggs than NPK but provided larvae with sufficient organic nutrients for their development. The combination of both NPK + plant matter provided the greatest attractiveness for gravid females and sufficient organic substance allowing mosquito larvae to grow. Physicochemical analyses of water containing NPK showed minerals only (NH4(+)+NO3(-)+P+K) whereas plant matter showed high content of carbon and nitrogen. The NPK + plant matter mixture contained both organic and minerals elements that favoured the proliferation of bacteria and then the development of mosquito larvae. These findings could lead to the development of new traps that could attract females mosquitoes and killed hatched larvae if mix with appropriate larvicides.

Review of Temephos Discriminating Concentration for Monitoring the Susceptibility of Anopheles labranchiae (Falleroni, 1926), Malaria Vector in Morocco.

In Morocco, the resistance monitoring of Anopheles labranchiae larvae to temephos is done using discriminating concentration of 0.125 mg, which is half of the WHO recommended dose for Anopheles. However, this dosage seemed to be too high to allow an early detection of the resistance and its revision was found necessary. The present study was carried out during May-June 2008 and 2009 in nine provinces from the north-west of the country. The aim was to determine the lethal concentrations LC100 of temephos for the most susceptible populations and to define the discriminating dosage as the double of this value. The bioassays were conducted according to WHO standard operating protocol to establish the dose-mortality relationship and deduct the LC50 and LC95. The results of this study indicated that the LC100 obtained on the most susceptible populations was close to 0.05 mg/L. Therefore, the temephos discriminating dosage for susceptibility monitoring of An. labranchiae larvae in Morocco was set to be 0.1 mg/L.

[Guidelines for phase III evaluation of vector control methods against malaria]. / Guide pour l'évaluation en Phase III de la lutte antivectorielle contre le paludisme.

Most new vector control methods against malaria involve the use of pesticides. Prior to release of these products for general use, their efficacy, persistence, and cross-resistance must be tested on mosquito colonies raised in the laboratory (phase I) then on wild mosquitoes in the field (small-scale), individual dwellings, or experimental huts (phase II). The goal of phase III studies is to evaluate the efficacy and effectiveness of the vector-control product or method against malaria in a population at regular risk for transmission. The main objective of phase III tests is to measure the epidemiologic impact, e.g. on the incidence or prevalence of malaria in humans. This article presents guidelines for carrying out phase III tests of vector-control methods against malaria (e.g. home insecticide spraying or insecticide-impregnated bednet use). It was written by participants in a workgroup formed to define recommendations for the WHOPES (WHO Pesticide Evaluation Scheme).

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.

Preliminary field testing of a long-lasting insecticide-treated hammock against Anopheles gambiae and Mansonia spp. (Diptera: Culicidae) in West Africa.

The efficacy of an experimental long-lasting insecticide-treated hammock (LLIH) with a long-lasting treated net used as a blanket and made of the same fabric (polyethylene) was tested in a concrete block experimental hut, against the malaria vector Anopheles gambiae s.l. and the arbovirus vectors and nuisance mosquitoes Mansonia africana (Theobald) and Mansonia uniformis (Theobald). The LLIH was treated with the pyrethroid insecticide permethrin. It was evaluated concurrently with ignited mosquito coils over 20 successive weeks. In total, 2,227 mosquitoes (130 An. gambiae and 2,097 Mansonia spp.) corresponding to 27.8 mosquitoes per trap-night were collected in the untreated hut (control). The repellent effect of both coils and LLIH significantly reduced the number of mosquitoes entering the huts (35- 60%). There was no significant difference between LLIH and mosquito coils in blood-feeding inhibition (93-97%) or in mortality (88-98%). The LLIH is more cost-effective and user-friendly than mosquito coils, which need to be replaced nightly to protect people sleeping indoors from mosquito bites. The effects of LLIH on exophagic vectors also need to be investigated because most people that sleep in hammocks are outdoors.

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.

A biological test to quantify pyrethroid in impregnated nets.

First instar larvae of Aedes aegypti (L.) (Diptera: Culicidae) are very susceptible to deltamethrin, which kills all larvae at a very low dose (0.1 microg/l). Thus the sensitivity of this insect to detect that pyrethroid is in parts per billion, as obtained with most common chromatographic methods of analysis. Here we describe a biological test (BT) to quantify deltamethrin in long-lasting insecticidal nets (LLINs) by exposing first instar larvae of Ae. aegypti to serial extracted insecticide solutions from net samples. The deltamethrin concentration in the net was calculated at the doses killing 50% of larva, from the LC(50) of deltamethrin (6.5 x 10(-5) mg/l) and the dilution factor (DF(50)) of the extracted net solution. The pyrethroid quantification in LLINs after 0-25 washes with this BT was correlated with those obtained by direct chromatographic analysis (r(2) = 0.84). This BT did not require sophisticated equipment and could be extended to other molecules and materials. It appeared accurate, robust, cheap and well adapted to the national malaria programmes as the eggs of Ae. aegypti might be used for some months. This method was adapted to provide an easy to use kit test for the quality control of LLINs in the field.

Efficacy of mosquito netting for sustainable small holders' cabbage production in Africa.

The efficacy of a mosquito netting to protect cabbages, Brassica oleracea L., against pests was investigated in field trials in Benin, West Africa. A polyester net covered the plants at night by using a wood armature. The net was removed during the day to prevent overheating and excessive shade, both problems of insect-proof screens used under tropical conditions. The number of all lepidopteran larvae with netting protection and foliar insecticide sprays was significantly lower than the unprotected control. The number of diamondback moth, Plutella xylostella (L.), was significantly lower with netting protection compared with foliar insecticide sprays and control. Netting treated with deltamethrin gave total protection of young plants against the aphid Lipaphis erysimi (Kaltenbach). At harvest, the number of marketable cabbages protected with untreated netting was significantly higher compared with the production with foliar insecticide sprays. The protection of cabbages with netting can be an economically viable method. Considering the price of cabbages on local markets (US dollars 1/unit), the net returns per 100 m2 were US dollars 247 by using netting, US dollars 149 by using insecticides, and US dollars 117 for controls. The net returns for using netting are based on replacing the netting each crop cycle. But netting can be reused several times, depending upon conditions, increasing the profit margin. The netting protection may be an alternative to the growing unsustainable practices of vegetable cropping in peri-urban areas of tropical countries.

The indoor use of plastic sheeting pre-impregnated with insecticide for control of malaria vectors.

OBJECTIVE: To evaluate the efficacy of permethrin-treated plastic sheeting (ITPS) applied as a lining to the ceiling or walls of rooms against pyrethroid-susceptible and pyrethroid-resistant Anopheles gambiae. METHOD: Overnight tests were carried out in veranda-trap experimental huts in Vallée du Kou, where two molecular forms of A. gambiae, S and M, occur. The S form is mostly pyrethroid resistant due to the kdr mechanism, and the M form is mostly kdr susceptible. A variety of ITPS covered surfaces were tested, ranging from ceiling only to all walls plus ceiling covered. RESULTS: ITPS had a major effect on the mortality of mosquitoes, the proportion killed being dependent upon the surface area covered. Homozygotes for kdr resistance showed lower rates of mortality than did heterozygotes or homozygotes for susceptibility. Deterred entry of mosquitoes and inhibition of blood feeding were also correlated with surface area covered. The mode of action and efficacy of ITPS seems to bear closer resemblance to that induced by indoor residual spraying (IRS) than to that induced by insecticide-treated nets. CONCLUSIONS: ITPS might be conceived as being equivalent to long-lasting or permanent IRS but without some of the operational constraints normally associated with spraying. High coverage of ITPS could potentially have a mass population effect on mosquitoes and give rise to long-term community protection against malaria. A phase III trial is justified to assess the acceptability of ITPS and its efficacy against malaria.

[Vectorial transmission of malaria in shrubby Savannah area at Ganse, Ivory Coast]. / Transmission vectorielle du paludisme en savane arborée a Ganse en Côte d'Ivoire.

A longitudinal entomologic study was carried out in the village of Ganse located in the Northeastern Ivory Coast from July 2000 to July 2001. The threefold purpose of the study was to index Plasmodium-carrying Anopheles species by capturing mosquitoes on human volunteers, collecting larvae in different dwelling types, and evaluating the involvement each species in the malaria transmission. A total of 4 species belonging to the Anopheles genus were collected in the village. Identification of circumsporozoite protein using the ELISA technique demonstrated that three species were plasmodium vectors. These species belonged to the An. gambiae complex (An. gambiae s.s. 100%), to the An. funestus group (An. funestus s.s. 95.6%) and to the An. nill group (An. nili s.s. 100%). The estimated mean sporozoite index was 5.9% for An. gambiae s.l., 4.3% for the An. funestus group and 2.6% for the An. nili group. The main larva breeding sites were standing water such as puddles for An. gambiae s.l., streams with tall plants for the An. funestus group and the Comoe River for An. nili group. Because peak breeding of these three species occurs at three successive times; i.e., in May, September and July respectively, transmission of P. falciparum is continuous throughout the year. The transmission rate is high since we recorded up to up to 410 infected bites per person per year. In addition to showing the presence of An. rivulorum-like, our findings in the area demonstrates the important role of An. nili s.s. in the transmission and the complexity of the vectorial system.

Transmission vectorielle du paludisme en savane arborée à Gansé en Cote d'Ivoire

Un suivi entomologique longitudinal a ete realise a Ganse; un village du Nord-Est de la Cote d'Ivoire; entre juillet 2000 et juillet 2001. L'objectif de cette etude etait de repertorier les especes vectrices des Plasmodium par capture des moustiques sur des volontaires; recolter des larves dans diff e rents types de gites et evaluer l'implication de ces especes dans la transmission du paludisme. Quatre especes appartenant au genre Anopheles ont ete recoltees dans le village. La technique ELISA d'identification des antigenes CSP de Plasmodium a montre que trois de ces especes etaient ve c t rices. Ces especes appartenaient au complexe An. gambiae (An. gambiae s.s. a 100); au groupe An. funestus (An. funestus s.s. a 95;6) et au groupe An. nili (An. nili s.s. a 100). Les indices sporozoitiques moyen etaient de 5;9pour An. gambiae s.l.; 4;3pour les Anopheles du groupe funestus et 2;6pour les Anopheles du groupe nili. Les principaux gites larvaires etaient des points d'eau temporai es tels que des flaques pour An. gambiae s.l.; des cours d'eau a vegetation dressee pour les Anopheles du groupe funestus et le fleuve Comoe pour les Anopheles du groupe nili. La presence de ces trois especes avec des pics d'abondance observes respectivement en mai; en septembre et en juillet; assure une transmission quasi permanente de P. falciparum. Cette transmission est importante car on a pu enregistrer jusqu'a 410 piqures infectees par homme et par an. Dans cette localite; nous avons montre la presence d'An. rivulorum-like mais surtout le role important d'An. nili s.s. dans la transmission et la complexite du systeme vectoriel dans la region