Establishing baseline
insecticide discriminating doses is crucial in accurately determining susceptibility status and changing temporal patterns of physiological response in mosquito populations.
Pyrethroids are the predominant chemicals used for controlling adult Aedes aegypti and Ae. albopictus, both vectors of dengue viruses, in Thailand. Presently, only 2
pyrethroids,
permethrin and
lambda-cyhalothrin, have published diagnostic dose rates for monitoring Ae. aegypti. This study established the diagnostic lethal concentrations for 6 different
pyrethroids available in Thailand for
dengue vector control. United States Department of Agriculture
insecticide-susceptible strain of Ae. aegypti was used to establish the baseline concentrations for subsequent susceptibility testing of field populations. Our findings showed lower discriminating concentrations for
lambda-cyhalothrin and
permethrin than those recommended by the World Health Organization (WHO), at 2.5- and 1.7-fold lower dosing, respectively. The susceptibility status of 3 different geographical populations of field-collected Ae. aegypti were tested using the standard WHO procedures. All 3 field strains demonstrated varying levels of physiological resistance to each compound. We conclude that establishing the baseline diagnostic concentration of an
insecticide is of paramount importance in accurately determining the susceptibility status in field-collected mosquitoes. If possible, discriminating doses should be established for all
insecticides and test assays run concurrently with a known susceptible strain for more accurate monitoring of resistance in mosquito populations in Thailand.