Resistance of Aedes mosquito larvae to Temephos in the 8 provinces of northern Thailand, 2015-2016.

Abstract

Thailand has used Temephos to control Aedes mosquito larvae to prevent dengue fever for more than 50 years, but the insecticide monitoring system for young stages still does not exist. This study aims to assess the susceptibility level of Aedes aegypti to Temephos in   8 provinces of northern Thailand. Aedes mosquito larvae were collected in areas with dengue outbreaks in 2015 and 2016, Muang District Phayao, Lampang, Chiang Rai and Phrae Provinces, Pa Sang District, Lamphun Province, Tha Wang Pha District, Nan Province and Mae Sariang District, Mae Hong Son Province. All young stages of mosquitoes were transferred to the laboratory, then the 4th instar larvae were tested with Temephos at concentration 0.012 mg/L following World Health Organization Guideline. The results found that Ae. aegypti larvae from Nan Province for both years (2015-2016) were resistant to Temephos with a mortality rate 60% and 70%; aegypti larvae from Mae Hong Son, Chiang Mai, and Lampang provinces had 100 percent mortality rate in 2015, but changed to 34%, 40%, 62% respectively in 2016. Aedes from Phrae, Lumphun and Phayao have changed from incipient susceptible to resistance. Only Chiang Rai province showed higher susceptible level, from mortality rate 23% in 2015 and increased to 99% in 2016.

This study indicates that in 2016 Aedes aegypti has increased resistance trend to Temephos              in 6 provinces. The monitoring of Aedes susceptibility to Temephos should be regularly conducted for information of insecticide selection. Meanwhile, the simple way to prevent Dengue fever is breeding source reduction.