Temephos resistance of Aedes aegypti larvae in the area covered by the Office of Disease Prevention and Control Region 8, Udon Thani
The purpose of this study was to test temephos resistance of Aedes aegypti larvae in seven provinces covered by the office of Disease Prevention and Control Region 8, Udon Thani and the study was conducted between July-September 2018. Using a simple random sampling method, samples of Aedes aegypti larvae were collected from one representative village per province and the larval samples were looked after until they were in strong and normal conditions. The late third-stage and early fourth-stage larvae were selected for assay at the concentration of 0.0015-0.048 mg/L, which is in line with the recommendations by the World Health Organization (WHO). Data were analyzed using basic statistical methods and probit regression for LC50, as well as calculating for resistance ratio (RR). The results showed that the Bora-Bora strain of Aedes aegypti larvae tested under the concentration of 0.0015-0.048 mg/l had mortality rates of 13-100%, and the mortality rate of 100% at the concentration greater than or equal to 0.012 mg/L and the LC50 value was 0.003 mg/L. The local strains of Aedes aegypti larvae samples tested under the concentration 0.006-0.048 mg/L had mortality rates of 0-100%, the LC50 values were 0.011-0.037 mg/L and the temephos resistance ratios of 3.67-12.33. In conclusion, the Aedes aegypti larvae from Bung Kan province had the highest resistance to temephos, while moderate resistance to this chemical was found in larval samples from Nakhon Phanom, Loei, Sakon Nakhon, Nong Khai and Udon Thani provinces. Contrary to the above findings, larval samples from Nong Bua Lamphu province were found to be sensitive to temephos. The results of this study indicate that Aedes aegypti larvae from different locations had different resistance rates to temephos. The findings are useful for making decision with respect to the use of appropriate concentrations of temephos and time needed for controlling Aedes aegypti larvae populations based on the above mentioned temephos resistance rates. The area with higher temephos resistance ratios should take less time to control the Aedes aegypti larvae populations. In addition, temephos should be used when necessary so as to delay potential resistance of Aedes aegypti larvae to the chemical and temephos resistance should also be periodically monitored.
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