Laboratory and experimental hut trial evaluation of VECTRON™ T500 for indoor residual spraying (IRS) against insecticide resistant malaria vectors in Burkina Faso

Background: Malaria cases in some areas could be attributed to vector resistant to the insecticide. World Health Organization recommended insecticides for vector control are limited in number. It is essential to find rotational partners for existing Indoor Residual Spraying (IRS) products. VECTRON™ T500 is a novel insecticide with broflanilide as active ingredient. It has a mode of action on mosquitoes completely different to usually used. The aim of this study was to determine the optimum effective dose and efficacy of VECTRONTM T500 against susceptible and resistant strains of Anopheles in Burkina Faso. Methods: VECTRON™T500 was sprayed at 50, 100 and 200 mg/m² doses onto mud and concrete blocks using Potter Spray Tower. The residual activity of broflanilide was assessed through cone bioassays 1 week and then monthly up to 14 months post spraying. Its efficacy was evaluated at 100 and 150 mg/m² against wild free-flying mosquitoes in experimental huts on both substrates. Actellic 300CS was applied at 1000 mg/m² as reference product. Cone assays were conducted monthly, using susceptible and resistant mosquito strains. Results: In the laboratory, VECTRON™ T500 showed residual efficacy (≥80% mortality) on An. gambiae Kisumu up to 12 and 14 months, respectively, on concrete and mud blocks. Similar results were found with 100 and 200 mg/m² using An. coluzzii pyrethroid resistant strain. In experimental huts, a total of 19,552 An. gambiae s.l. were collected. Deterrence, blood-feeding inhibition and exophily with VECTRON™ treated huts were very low. At 100 and 150 mg/m², mortality of wild An. gambiae s.l. ranged between 55% and 73%. Monthly cone bioassay mortality remained >80% up to 9 months. Conclusions: VECTRON™ T500 shows great potential as IRS formulation for malaria vector control. It can be added to the arsenal of IRS products for use in rotations to control malaria and manage mosquito insecticide resistance

A new WHO bottle bioassay method to assess the susceptibility of mosquito vectors to public health insecticides: results from a WHO-coordinated multi-centre study.

BACKGROUND: The continued spread of insecticide resistance in mosquito vectors of malaria and arboviral diseases may lead to operational failure of insecticide-based interventions if resistance is not monitored and managed efficiently. This study aimed to develop and validate a new WHO glass bottle bioassay method as an alternative to the WHO standard insecticide tube test to monitor mosquito susceptibility to new public health insecticides with particular modes of action, physical properties or both. METHODS: A multi-centre study involving 21 laboratories worldwide generated data on the susceptibility of seven mosquito species (Aedes aegypti, Aedes albopictus, Anopheles gambiae sensu stricto [An. gambiae s.s.], Anopheles funestus, Anopheles stephensi, Anopheles minimus and Anopheles albimanus) to seven public health insecticides in five classes, including pyrethroids (metofluthrin, prallethrin and transfluthrin), neonicotinoids (clothianidin), pyrroles (chlorfenapyr), juvenile hormone mimics (pyriproxyfen) and butenolides (flupyradifurone), in glass bottle assays. The data were analysed using a Bayesian binomial model to determine the concentration-response curves for each insecticide-species combination and to assess the within-bioassay variability in the susceptibility endpoints, namely the concentration that kills 50% and 99% of the test population (LC50 and LC99, respectively) and the concentration that inhibits oviposition of the test population by 50% and 99% (OI50 and OI99), to measure mortality and the sterilizing effect, respectively. RESULTS: Overall, about 200,000 mosquitoes were tested with the new bottle bioassay, and LC50/LC99 or OI50/OI99 values were determined for all insecticides. Variation was seen between laboratories in estimates for some mosquito species-insecticide combinations, while other test results were consistent. The variation was generally greater with transfluthrin and flupyradifurone than with the other compounds tested, especially against Anopheles species. Overall, the mean within-bioassay variability in mortality and oviposition inhibition were < 10% for most mosquito species-insecticide combinations. CONCLUSION: Our findings, based on the largest susceptibility dataset ever produced on mosquitoes, showed that the new WHO bottle bioassay is adequate for evaluating mosquito susceptibility to new and promising public health insecticides currently deployed for vector control. The datasets presented in this study have been used recently by the WHO to establish 17 new insecticide discriminating concentrations (DCs) for either Aedes spp. or Anopheles spp. The bottle bioassay and DCs can now be widely used to monitor baseline insecticide susceptibility of wild populations of vectors of malaria and Aedes-borne diseases worldwide

Pesticides Ecotoxicological Risk Assessment for Surface Waters in the Cotton Growing Area Around the Bala’s Hippopotamus Pond Biosphere Using PIRI Method

Pesticides residues are frequently found in the environment far from the original point of their application. Besides the desired effects of pest control, non-target organisms, soil and water are contaminated by the pesticides. This paper presents results on the impact of these xenobiotics used in cotton cultivation on River "Wolo" environment in Burkina Faso by using the Pesticide Impact Rating Index (PIRI) software package. The assessment was based on the assumption of three scenarios taking into account the organic matter content of the soil and the presence of a buffer zone. Pesticides properties and use data, and data on the physical environment, were also used. Considering the worst case (scenario 2), diuron, haloxyfop-R-methyl, glyphosate and nicosulfuron were the most mobile. Diuron was classified as the most toxic pesticide to Scenedesmus quadricauda. Toxicity to Daphnia magna was extremely high with chlorpyrifos ethyl, very high with betacyfluthrin, deltamethrin, lamda-cyalothrin and high with flubendiamide. For Oncorhynchus mykiss, it was beta-cyfluthrin, deltamethrin and lamdacyhalothrin that caused a very high risk and chlorpyrifos ethyl and indoxacarb a high risk. For all pesticides, the risks are reduced overall depending on the width of the buffer zone and the organic matter content of the soil. The use of a pesticide in a given location must take into account its ecotoxicological impact on the surrounding ecosystem. Tools such as PIRI, could be used for the selection of pesticides to be used. Also, environmental parameters such as buffer zone and organic matter content should be used by farmers to limit the mobility of pesticides to water

Evidence that agricultural use of pesticides selects pyrethroid resistance within Anopheles gambiae s.l. populations from cotton growing areas in Burkina Faso, West Africa.

Many studies have shown the role of agriculture in the selection and spread of resistance of Anopheles gambiae s.l. to insecticides. However, no study has directly demonstrated the presence of insecticides in breeding sources as a source of selection for this resistance. It is in this context that we investigated the presence of pesticide residues in breeding habitats and their formal involvement in vector resistance to insecticides in areas of West Africa with intensive farming. This study was carried out from June to November 2013 in Dano, southwest Burkina Faso in areas of conventional (CC) and biological cotton (BC) growing. Water and sediment samples collected from breeding sites located near BC and CC fields were submitted for chromatographic analysis to research and titrate the residual insecticide content found there. Larvae were also collected in these breeding sites and used in toxicity tests to compare their mortality to those of the susceptible strain, Anopheles gambiae Kisumu. All tested mosquitoes (living and dead) were analyzed by PCR for species identification and characterization of resistance genes. The toxicity analysis of water from breeding sites showed significantly lower mortality rates in breeding site water from biological cotton (WBC) growing sites compared to that from conventional cotton (WCC) sites respective to both An. gambiae Kisumu (WBC: 80.75% vs WCC: 92.75%) and a wild-type strain (49.75% vs 66.5%). The allele frequencies L1014F, L1014S kdr, and G116S ace -1R mutations conferring resistance, respectively, to pyrethroids and carbamates / organophosphates were 0.95, 0.4 and 0.12. Deltamethrin and lambda-cyhalothrin were identified in the water samples taken in October/November from mosquitoes breeding in the CC growing area. The concentrations obtained were respectively 0.0147ug/L and 1.49 ug/L to deltamethrin and lambdacyhalothrin. Our results provided evidence by direct analysis (biological and chromatographic tests) of the role of agriculture as a source of selection pressure on vectors to insecticides used in growing areas

Efficacy of PermaNet^® 3.0 and Interceptor^® nets tested against susceptible and wild populations of <i>An</i>. <i>gambiae</i> s.l. study sites.

<p>Efficacy of PermaNet^® 3.0 and Interceptor^® nets tested against susceptible and wild populations of <i>An</i>. <i>gambiae</i> s.l. study sites.</p

Mortality rates of <i>Anopheles gambiae</i> s.l. from two study sites observed after exposure to 0.05% deltamethrin and 0.1% bendiocarb.

<p>Mortality rates of <i>Anopheles gambiae</i> s.l. from two study sites observed after exposure to 0.05% deltamethrin and 0.1% bendiocarb.</p

Efficacy of PermaNet^® 3.0 and Interceptor^® nets tested against susceptible and wild populations of <i>An</i>. <i>gambiae</i> s.l. study sites.

<p>Efficacy of PermaNet^® 3.0 and Interceptor^® nets tested against susceptible and wild populations of <i>An</i>. <i>gambiae</i> s.l. study sites.</p

Figure showing the location of the cotton region since 1960 in Burkina Faso and the sampling sites (Dano, Soumousso and Bobo-Dioulasso).

<p>The study took place near the town of Dano in two neighboring villages (Kompla and Dobao).</p

GC-μECD chromatogram of a sediment sample taken from a conventional cotton field (Kompla) before insecticide treatment showing the presence of diuron at a concentration of 105mm / kg soil.

<p>GC-μECD chromatogram of a sediment sample taken from a conventional cotton field (Kompla) before insecticide treatment showing the presence of diuron at a concentration of 105mm / kg soil.</p

GC-μECD chromatograms of a water sample from a conventional cotton growing area after insecticide treatment of cotton fields showing the presence of deltamethrin and lambdacyhalothrin.

<p>GC-μECD chromatograms of a water sample from a conventional cotton growing area after insecticide treatment of cotton fields showing the presence of deltamethrin and lambdacyhalothrin.</p