Abstract
BackgroundMalaria vector control is dependent on chemical insecticides applied to walls by indoor residual spraying or on long-lasting insecticidal nets. The emergence and spread of insecticide resistance in major malaria vectors may compromise malaria control and elimination efforts. The aim of this study was to estimate a diagnostic dose for chlorfenapyr (class: pyrrole) and clothianidin (class: neonicotinoid) and assess the baseline susceptibility of three major Anopheles malaria vectors of western Kenya to these two insecticides.MethodsThe Centers for Disease Control and Prevention (CDC) bottle assay was used to determine the diagnostic doses of chlorfenapyr and clothianidin insecticides against the susceptible Kisumu strain of Anopheles gambiae. Probit analysis was used to determine the lethal doses at which 50% (LD50) and 99% (LD99) of the susceptible mosquitoes would be killed 24, 48 and 72 h following exposure for 1 h. Insecticidal efficacy of chlorfenapyr, clothianidin and the pyrethroid deltamethrin was then evaluated against field collected female Anopheles mosquitoes sampled from Nyando, Bumula and Ndhiwa sub-Counties in western Kenya. Members of Anopheles funestus and An. gambiae complexes were identified using polymerase chain reaction (PCR).ResultsThe determined diagnostic doses of chlorfenapyr and clothianidin insecticides were 50 µg/bottle and 150 µg/bottle, respectively, for An. gambiae, Kisumu strain. When exposed to the diagnostic dose of each insecticide, Anopheles malaria vector populations in western Kenya were susceptible to both insecticides with 100% mortality observed after 72 h. Mortality of mosquitoes exposed to deltamethrin increased over time but did not reach 100%. Mortality of Anopheles arabiensis from Nyando exposed to deltamethrin was 83% at 24 h, 88% at 48 h and 94.5% at 72 h while An. funestus from Ndhiwa was 89% at 24 h, 91.5% at 48 h and 94.5% at 72 h.ConclusionMosquitoes of western Kenya, despite being resistant to pyrethroids, are susceptible to chlorfenapyr and clothianidin. Field evaluations of the formulated product are needed.
Highlights
Malaria vector control is dependent on chemical insecticides applied to walls by indoor residual spraying or on long-lasting insecticidal nets
Clothianidin and deltamethrin against malaria vector populations of western Kenya A total of 2379 mosquitoes were tested for susceptibility to chlorfenapyr, clothianidin and deltamethrin by polymerase chain reaction (PCR) as shown in Fig. 3, all mosquitoes tested from Nyando subcounty were An. arabiensis (1133/1133), 96.5% (386/400) of mosquitoes tested from Bumula sub-County were An. gambiae s.s. and 3.5% (14/400) were An. arabiensis while 97.3% (827/850) of mosquitoes tested from Ndhiwa sub-county were An. funestus and 2.7% (23/400) were An. arabiensis
Anopheles populations of western Kenya showed 100% mortality in Centers for Disease Control and Prevention (CDC)-Bottle bioassays at 72 h post-exposure to both chlorfenapyr and clothianidin with resistance observed to deltamethrin insecticide in two study sites, even at 72 h post-exposure
Summary
Malaria vector control is dependent on chemical insecticides applied to walls by indoor residual spraying or on long-lasting insecticidal nets. The emergence and spread of insecticide resistance in major malaria vectors may compromise malaria control and elimination efforts. There are likely multiple reasons for the slowed progress in reducing malaria, but one likely reason is the emergence and spread of insecticide resistance in the major malaria vectors, a development that may compromise chemical based malaria control interventions and thereby threaten malaria control and elimination efforts. Pyrethroids are widely used for malaria vector control but resistance has developed in the major malaria vectors of Africa [5] and is present in nearly every country in sub-Saharan Africa [6] As new compounds are developed, it is essential to establish diagnostic concentrations to determine baseline susceptibility of malaria vectors and to enable surveillance of insecticide resistance once the insecticides are in use to guide National Malaria Control Programmes in the deployment and replacement of the insecticide-based vector control tools
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