title: Insecticide resistance and its underlying mechanisms in field populations of Aedes aegypti adults (Diptera: Culicidae) in Singapore.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  This study confirmed the presence of pyrethroid resistance among Ae. aegypti adults in Singapore and documented the early onset of organophosphate resistance.
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, S (138667), Singapore, ᅟ. koou_sin_ying@nea.gov.sg.|Urban Entomology Laboratory, Vector Control Research Unit, School of Biological Sciences, Universiti Sains Malaysia, 11800, Penang, Malaysia. koou_sin_ying@nea.gov.sg.
authors.forename: Sin-Ying
authors.initials: SY
authors.lastname: Koou
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, S (138667), Singapore, ᅟ. chong_chee_seng@nea.gov.sg.
authors.forename: Chee-Seng
authors.initials: CS
authors.lastname: Chong
authors.affiliation: Parasitology Department, Faculty of Medicine, University of Malaya, 50603, Kuala Lumpur, Malaysia. indra.vythilingam@gmail.com.
authors.forename: Indra
authors.initials: I
authors.lastname: Vythilingam
authors.affiliation: Urban Entomology Laboratory, Vector Control Research Unit, School of Biological Sciences, Universiti Sains Malaysia, 11800, Penang, Malaysia. chowyang@usm.my.
authors.forename: Chow-Yang
authors.initials: CY
authors.lastname: Lee
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way #06-05/08, Helios Block, S (138667), Singapore, ᅟ. ng_lee_ching@nea.gov.sg.
authors.forename: Lee-Ching
authors.initials: LC
authors.lastname: Ng
mesh_terms: D000330:Aedes / Q000187:drug effects*; D000818:Animals; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D010755:Organophosphates / Q000494:pharmacology; D009946:Organothiophosphorus Compounds / Q000494:pharmacology*; D011722:Pyrethrins / Q000494:pharmacology*; D012846:Singapore
chemical_list: D007306:Insecticides; D010755:Organophosphates; D009946:Organothiophosphorus Compounds; D011722:Pyrethrins; C014153:pirimiphos methyl