Diagnostic dose determination and efficacy of chlorfenapyr and clothianidin insecticides against Anopheles malaria vector populations of western Kenya

Abstract

Background 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. 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. Methods The 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). Results The 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. Conclusion Mosquitoes of western Kenya, despite being resistant to pyrethroids, are susceptible to chlorfenapyr and clothianidin. Field evaluations of the formulated product are needed. Electronic supplementary material The online version of this article (10.1186/s12936-019-2858-z) contains supplementary material, which is available to authorized users.

Resistance to clothianidin reduces the efficacy of SumiShield® 50WG, a neonicotinoid formulation for indoor residual spraying, againstAnopheles gambiae

“…Despite these difficulties, the susceptibility of wild Anopheles populations from several African countries has been successfully evaluated using the recommended diagnostic doses of clothianidin [18,22,35,37 arabiensis [18,22,35,37]. Resistance to clothianidin was not detected among populations from 16 countries where 100% mortality was reached on average 72 h following exposure in all populations tested either with WHO tube tests [18,37] or with CDC bottle assays [22,35]. Our study confirms that susceptible populations of [18].…”

“…We tested the susceptibility of adult mosquitoes against a diagnostic dose of clothianidin using CDC bottle assays according to published guidelines [34]. A recent study showed that 150µg/ml clothianidin was a suitable diagnostic dose-the lowest concentration of active ingredient that kills 100% of individuals of a susceptible laboratory strain within 24 h of insecticide exposure [35]. To assess the intensity of resistance, we also determined the mortality rates of wild mosquitoes exposed to 5X and 10X the diagnostic dose.…”

“…coluzzii (n = 673) and Culex sp (n = 132). To validate the CDC bottle bioassay protocol [35], we first analyzed susceptibility in 554 individuals of two laboratory colonies: An. gambiae Kisumu (n = 326) and An.…”

“…Assessing clothianidin susceptibility in Anopheles mosquitoes using conventional bioassays has been met with some technical challenges so far [18,22,35,37,44]. Clothianidin is difficult to solubilize in solvents commonly used in bioassays, which has made the design of standard protocols more laborious than usual [18,35,37]. In addition, because this active ingredient acts slowly, resistance profiles are revealed via laboratory bioassays only if exposed populations are rigorously monitored during a long holding period, which can last seven days or more.…”

“…In addition, because this active ingredient acts slowly, resistance profiles are revealed via laboratory bioassays only if exposed populations are rigorously monitored during a long holding period, which can last seven days or more. Despite these difficulties, the susceptibility of wild Anopheles populations from several African countries has been successfully evaluated using the recommended diagnostic doses of clothianidin [18,22,35,37 arabiensis [18,22,35,37]. Resistance to clothianidin was not detected among populations from 16 countries where 100% mortality was reached on average 72 h following exposure in all populations tested either with WHO tube tests [18,37] or with CDC bottle assays [22,35].…”