Evaluation of the residual effectiveness of Fludora™ fusion WP-SB, a combination of clothianidin and deltamethrin, for the control of pyrethroid-resistant malaria vectors on Bioko Island, Equatorial Guinea.

Over the past decade, insecticide resistance to malaria vectors has been identified in 71 malaria endemic countries. This has posed a major global health challenge in the fight against malaria, with declining rates of indoor residual spraying coverage attributed to pyrethroid-resistance. As part of its vector control monitoring strategies, the Bioko Island Malaria Control Project (BIMCP) in Equatorial Guinea conducted routine insecticide resistance bioassays using the WHO's standard susceptibility tests from 2013 to 2018. During the same period, the frequency of the target-site knockdown resistance allele (kdr) in the local vector population was also determined via PCR for detection of the L1014 F mutation. Biochemical analysis for metabolic resistance was also conducted in 2015. From 2016-2017, Fludora™ fusion, a formulated combination of clothianidin (a neonicotinoid) and deltamethrin (a pyrethroid) was evaluated for 9 months on Bioko Island, using the WHO's standard test procedure for determining residual effectiveness of insecticides on sprayed surfaces. In 2016, the mortality rate of the vectors on 0.05% deltamethrin was as low as 38%. The frequency of the West African form of knockdown resistance allele, L1014 F, in the vector population was as high as 80%, and metabolic resistance analysis indicated high upregulated cytochrome P450 s. However, the residual effectiveness of Fludora™ fusion recorded mortalities above 80% after 72 h of exposure for 8 months. Although both target-site knockdown resistance and metabolic resistance to pyrethroids were implicated in the local malaria vector population, Fludora™ fusion was effective under field conditions in controlling the resistant vectors for a period of 8 months on wooden surfaces on Bioko Island and represents a valuable addition to IRS programs, especially in regions with high levels of pyrethroid resistance.