Long-lasting Residual Efficacy of Actellic ® 300CS and Icon ® 10CS on Different Surfaces against Anopheles stephensi, an Invasive Malaria Vector

Abstract

Abstract Background: Anopheles stephensi, an invasive malaria vector, has developed resistance to several commonly used insecticides, including DDT, Dieldrin, Malathion, and synthetic pyrethroids. In response to this challenge, the World Health Organization (WHO) has recommended the use of Actellic®300CS and Icon®10CS for Indoor Residual Spraying (IRS) to control pyrethroid-resistant mosquitoes. This study aimed to assess the current susceptibility status of An. stephensi to the Diagnostic Concentration (DC) of some insecticides in Iran, and the residual effectiveness of Actellic®300CS and Icon®10CS against this malaria vector. Method: Susceptibility of An. stephensi populations from the south of Iran was evaluated against Deltamethrin 0.05%, DDT 4%, Malathion 5%, Bendiocarb 0.1%, Synergist assay PBO 4% with Deltamethrin 0.05%, and intensity assay with 5x DC of Deltamethrin (0.25%) and Bendiocarb 0.5%. Laboratory cone bioassay tests for evaluation of the residual efficacy of Actellic®300 and Icon®10CS insecticides on different surfaces commonly found in human dwellings, such as cement, mud, plaster, and wood were conducted by using the WHO test kits and the standard testing protocols. Results: The An. stephensi populations in Bandar Abbas were found to be sensitive to Malathion 5% and Deltamethrin 0.25% (5X DC) but resistant to DDT, Deltamethrin 1x DC, and Bendiocarb (1x DC and 5X DC). In laboratory cone bioassay tests, the mortality rates of An. stephensi exposed to Actellic®300CS and Icon®10CS on various surfaces were consistently above 80% for Actellic®300CS on all substrates throughout the 300-day after-spraying period. However, for Icon®10CS, the mortality rates were above 80% on plaster and wood substrates for 165 days and on mud and cement substrates for 270 days after spraying. Both Actellic®300CS and Icon®10CS showed 100% mortality 72 hours after each test on all substrates for the entire 300-day after-spraying period. Discussion and Conclusion: The study highlights the varying levels of resistance of An. stephensi Hormoodar populations to different insecticides and demonstrates the consistent performance of Actellic®300CS in controlling these mosquitoes on various surfaces. The findings suggest that long-lasting CS formulations may be more effective for malaria vector control compared to the current options. Further research is needed to validate these findings in field settings and assess the impact of these insecticides on malaria transmission.