Insecticide resistance in Aedes aegypti from the National Capital Region, Philippines

BackgroundHuman arboviral diseases such as dengue, chikungunya and Zika can be transmitted by the mosquito Aedes aegypti. The insecticide-based vector control strategy is critical in reducing the transmission of these Aedes-borne diseases but is threatened mainly by the emergence of insecticide resistance. Methodology/Principal FindingsAdult Aedes aegypti from National Capital Region, Philippines were subjected to bioassay to determine their susceptibility to the diagnostic doses of pyrethroid, organochlorine and organophosphate insecticides following the standard World Health Organization insecticide susceptibility test. This study reports for the first time the existence of insecticide resistance in Ae. aegypti from the Philippines to pyrethroids and organochlorine. Results from this study showed that most of the Ae. aegypti populations exhibited phenotypic resistance to the pyrethroids (permethrin and etofenprox) and an organochlorine (DDT) while all populations tested to malathion were still susceptible to this organophosphate. Varying resistance levels to deltamethrin, cyfluthrin and lambdacyhalothrin were also observed in the different mosquito populations. ConclusionsInsecticide resistance exists in local populations of Ae. aegypti from the National Capital Region. This finding should alert public health authorities to consider modifying the existing vector management package for greater control efficacy. Best practices that are proven to prevent and/or delay the development of insecticide resistance such as insecticide rotation should be implemented. Alternative toxicants and chemicals with a different mode of action, such as repellents, should be explored to ensure continuing efficacy of program interventions. Author summaryThe National Capital Region (NCR), Philippines reports the countrys highest dengue incidence. Apart from being populous and the center of economic activity, the local government authorities of this region have undertaken significant vector control efforts devoted to dengue. The use of insecticides to reduce mosquito vector density remains the handiest control method. This scenario necessitated the documentation of the resistance levels, particularly of the most important vector Aedes aegypti. An insect is said to be resistant when the known effective dose of an insecticide can no longer sufficiently kills the same insect population. This study showed that Ae. aegypti population from cities in NCR had developed resistance to commonly used pyrethroids (permethrin, etofenprox) and to an organochlorine (DDT). Highly localized variations of resistance and susceptibility within cities at NCR were recorded against deltamethrin, cyfluthrin and lambdacyhalothrin. This finding should alert public health authorities to consider modifying the existing vector management package for greater control efficacy.