Biological Efficacy of an Adulticide Mixture (clothianidin + deltamethrin) as an Indoor Residual Spray against Adult Anopheles flavirostris in Palawan, the Philippines

To reach the goal of malaria-free Philippines status by 2030, there is a need to address the issue of insecticide resistance. An option to address such goal would need an alternative product for vector control – one of which is the use of an insecticide mixture. The study was conducted to evaluate the killing efficacy and persistence of a new adulticide mixture of clothianidin and deltamethrin (Fludora Fusion) against adult Anopheles flavirostris mosquitoes on different surfaces under field conditions in the village of Bacungan, Puerto Princesa City, Palawan from 2017-2018. Houses made up of wood and cemented walls were selected and sprayed with Fludora Fusion (Clothianidin + deltamethrin 10g/L), in comparison to Ficam 80 WP (bendiocarb 12.5g/L) and Victor 20 WP using two concentrations (etofenprox 20WP 25g/L and etofenprox 12.5/L). Wild-caught Anopheles flavirostris was subjected to the WHO cone bioassay test for the observation of knockdown (after 1 hour), immediate (24 hours), and delayed mortality effects (72 hours) from the baseline up to 6 months after indoor residual treatment. Biological efficacy tests showed that all products met the 80% mortality at the initial test, but their killing effect decreased across months. Generally, insecticides sprayed on wooden surfaces performed better than on cemented walls. Among them, the Fludora Fusion has consistently met the WHO cutoff values of 80% mortality. Its killing effects are found to be significantly (p < 0.0001) greater than those of the other products tested, with higher mortality rates observed after 72 hours. Only Fludora Fusion (clothianidin + deltamethrin) adulticide mixture formulation has ≥80% mortality after 6 months. The susceptibility of the specimens used in the bio-assays was tested using the WHO procedure. Results revealed Anopheles flavirostris incipient resistance to alpha-cypermethrin (96.5%), and full susceptibility to 11 insecticides (permethrin (99%), cyfluthrin (98.9%), lambda-cyhalothrin (99%), malathion (100%), fenitrothion (100%), pirimiphos-methyl (100%), propoxur (100%), and DDT (100%)) including the active ingredients (deltamethrin (100%), etofenprox (100%) and bendiocarb (100%)) component of the insecticide products evaluated.