Insecticide susceptibility and selection for resistance in a population of Aedes aegypti from Ratchaburi province, Thailand.

The insecticide susceptibility of Aedes aegypti larvae and adults from four areas of Ratchaburi Province, Thailand was investigated using World Health Organization standard procedures. The larvae of Ae. aegypti in all areas were found to be susceptible to temephos. The strain with the highest level of temephos resistance was subjected to temephos selection. The resistance ratios increased to 2.74-fold from their parental non selected strain after 5 generations of selection. For the adult of Ae. aegypti, the study was conducted to determine the effects of 0.75 % permethrin and 0.05 % deltamethrin impregnated paper selection on the strain having the highest with the highest LT50 level. The results showed the increase in the LT50 to 7.46 and 1.18-fold after the third se lected generation with 0.75 % permethrin and 0.05 % deltamethrin respectively. Mortality rates after exposing adults to discriminating concentrations showed that field populations in Ratchaburi Province were resistant to permethrin and deltamethrin. Alternative non-chemical measures need to be used in new of the emergence of resistance in the mosquito population. INTRODUCTION Dengue is the most important arthropod-borne viral disease in Southeast Asia (WHO, 2000). The principal vector of dengue virus in Thailand is the mosquito Aedes (Stegomia) aegypti (L .). Until an effective, safe and affordable vaccine become available, no adequate prevention or control measures other than control of vector, Ae. aegypti, are available to deal with epidemics of disease(Gratz,1993). A vaccine against dengue is currently not available and the control of is likely to remain vector control(Pan-American Health Organization, 1998). Although reduction of sources in which the mosquitoes develop can keep vector populations low, the use of insecticides is often necessary. The primary insecticides used against dengue vector in