Abstract
BackgroundControl of the Anopheline mosquito vectors of malaria by use of insecticides has been shown to impact on both morbidity and mortality due to this disease. Evidence of insecticide resistance in different settings necessitates surveillance studies to allow prompt detection of resistance should it arise and thus enable its management. Possible resistance by Anopheles arabiensis mosquitoes from Mwea rice irrigation scheme in Central Kenya to insecticides in the four classes of insecticides approved by WHO for indoor residual spraying was investigated.MethodsSusceptibility to DDT (an organochlorine), fenitrothion (an organophosphate), bendiocarb (a carbamate), lambdacyhalothrin and permethrin (both pyrethroids) was tested using standard WHO diagnostic bioassay kits. Bioassays were performed on non-blood fed mosquitoes one- to three-day old. Knockdown was recorded every 10 min and mortality 24 h post-exposure was noted.ResultsMortality 24 h post-exposure was 100% for all insecticides except for lambdacyhalothrin, which averaged 99.46%. Knockdown rates at 10 min intervals were not significantly different between the Mwea population and the susceptible KISUMU strain of Anopheles gambiae sensu stricto control. The KDT50 and KDT95 values for the Mwea population were either lower than those for the control or higher by factors of no more than 2 for most comparisons and compared well with those of An. gambiae sensu lato categorized as susceptible in other studies.ConclusionThese results suggest that the Mwea population of An. arabiensis is susceptible to all the insecticides tested. This implies that vector control measures employing any of these insecticides would not be hampered by resistance.
Highlights
Control of the Anopheline mosquito vectors of malaria by use of insecticides has been shown to impact on both morbidity and mortality due to this disease
More recent studies indicate that resistance levels have increased only marginally [7], there is concern that continued and/or increased use of insecticides may result in increased resistance that would threaten the sustainability of this vector control strategy
An interview with a manager at the Mwea Rice Growers Multipurpose Co-operative Society, the organization that supplies the pesticides to the farmers and through which the farmers sell their produce revealed that fenitrothion alongside carbofuran have been the pesticides in use for agricultural spraying but the use carbofuran was stopped two years prior to the study due to cost factors
Summary
Control of the Anopheline mosquito vectors of malaria by use of insecticides has been shown to impact on both morbidity and mortality due to this disease. Studies show that the use of insecticides both for Indoor Residual Spraying (IRS) programmes and in the treatment of bed nets has resulted in a reduction in vector population densities and in morbidity and mortality due to malaria [2,3,4]. The dominant resistance mechanisms vary as was observed in Guatemalan populations of Anopheles albimanus, where both insecticide resistance levels and mechanism varied within short distances [12]. These observations suggest the shifting nature of insecticide resistance and imply that extrapolations from one circumstance to another may be misleading. Studies in Haitian populations of An. albimanus found resistance frequencies to fenitrothin to increase from 20 to 60% over a period of six months [13] and underscore the need for continuous insecticide resistance monitoring, even where no evidence of resistance has previously been found
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