Abstract
In Singapore, dose–response bioassays of Aedes aegypti (L.) adults have been conducted, but the mechanisms underlying resistance to insecticides remain unclear. In this study, we evaluated insecticide resistance and its underlying mechanism in field populations of Ae. aegypti adults. Seven populations of Ae. aegypti were collected from public residential areas and assays were conducted according to WHO guidelines to determine their susceptibility to several commonly used insecticides. Various levels of pyrethroid resistance (RR50 = 3.76 to 142.06-fold) and low levels of pirimiphos-methyl resistance (RR50 = 1.01 to 1.51-fold) were detected. The insecticide susceptibility profile of Ae. aegypti adults was homogenous among the different study sites. Addition of the synergists piperonyl butoxide, S,S,S,-tributyl phosphorotrithioate, and triphenyl phosphate generally failed to enhance the toxicity of the insecticides investigated, suggesting an insignificant role of metabolic-based insecticide resistance and possible involvement of target site resistance. Further biochemical investigation of specific metabolic enzyme activities provided further evidence that detoxifying enzymes such as mono-oxygenases, esterases, glutathione S-transferases and altered acethylcholinesterases generally did not contribute to the resistance observed. This study confirmed the presence of pyrethroid resistance among Ae. aegypti adults in Singapore and documented the early onset of organophosphate resistance.
Highlights
In Singapore, dose–response bioassays of Aedes aegypti (L.) adults have been conducted, but the mechanisms underlying resistance to insecticides remain unclear
The objective of this study was to assess the extent of insecticide resistance and characterize the underlying mechanisms that may potentially play a role in the resistance
The toxicity levels of the five insecticides tested decreased in the following order: deltamethrin > cypermethrin > pirimiphos-methyl > permethrin > etofenprox
Summary
In Singapore, dose–response bioassays of Aedes aegypti (L.) adults have been conducted, but the mechanisms underlying resistance to insecticides remain unclear. Dengue viruses are transmitted by Aedes mosquitoes, and Aedes aegypti (L.) is the primary dengue vector in Singapore. This species has diurnal blood-feeding behaviour, with peak activities in the early morning and late afternoon. It is highly anthropophilic and displays a preference to feed and rest indoors or in close proximity to their breeding sites [4,5]. Detection of the adult can be difficult, where they can rest undisturbed in sheltered areas
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