Assessing the susceptibility and efficacy of three public health, insecticides, chlorfenapyr, clothianidin, and pyriproxyfen, on wild pyrethroid-resistant populations of Anopheles gambiae s.l. from southern Benin

Abstract Background : The objective of this study was to determine the susceptibility of wild Anopheles gambiae s.l. from southern Benin to the new insecticides (chlorfenapyr (CFP), pyriproxyfen (PPF), and clothianidin (CTD)) and assess the efficacy of insecticide-treated bed nets (ITNs) that contain these new products. Methods : Wild Anopheles gambiae s.l. from the Benin communes of Allada, Ifangni, Akpro-Missérété, and Porto-Novo were tested for their susceptibility to CFP and PPF using the WHO bottle tests, and pyrethroids (alpha-cypermethrin, deltamethrin, and permethrin) and CTD using WHO tube tests. WHO cone tests were used to evaluate the efficacy of Interceptor® (which contains alpha-cypermethrin (ACM) only), Interceptor® G2, (CFP + ACM), and Royal Guard® nets (PPF + ACM). The ovaries of blood-fed Anopheles gambiae s.l. from Ifangni exposed to a new PPF net were dissected, and egg development status was examined using Christopher’s stages to determine the fertility status of the mosquitoes. Using a standardized protocol, the oviposition rate and oviposition inhibition rate were calculated from live blood-fed Anopheles gambiae s.l. placed in oviposition chambers after exposure to PPF. Results . In all four mosquito populations, pyrethroid mortality ranged from 5% to 80%, while chlorfenapyr and clothianidin mortality ranged from 98% to 100%. At Ifangni, all mosquitoes exposed to Royal Guard® nets were infertile (100%) while the majority (74.9%) of mosquitoes exposed to Interceptor® nets had fully developed their eggs to Christopher’s stage V. The oviposition inhibition rate after exposure of the mosquitoes to the PPF was 99% for the wild population of Anopheles gambiae s.l. and the susceptible laboratory strain, Anopheles gambiae Kisumu. Conclusions : The results of this study suggest that pyrethroid-resistant Anopheles gambiae s.l. from the selected communes in southern Benin are susceptible to chlorfenapyr, clothianidin, and pyriproxyfen. In addition, based on bioassay results, Interceptor® G2 and Royal Guard® nets are probably effective in Ifangni. Despite the availability of new effective insecticides, continued vigilance is needed in Benin. Therefore, monitoring of resistance to these insecticides will continue to periodically update the Benin national insecticide resistance database and management plan.