Insecticide resistance of Aedes aegypti and Culex quinquefasciatus in Thailand

Abstract

Several countries continue to experience endemic and reemerging dengue fever (DF) and dengue hemorrhagic fever (DHF). 1) Annually, millions of people are estimated to be infected with dengue virus worldwide. 2,3) In Thailand, outbreaks of DHF were first recognized in 1958 and subsequently the disease has expanded throughout the country. 4) Approximately 40,000 cases of dengue with a mortality rate of 0.09 (per 100,000 people) were reported in 2007. 5) In spite of continued vigilance in control methods, dengue cases remain a major health threat in Thailand. The reason is unclear but is possibly related to the increase of human and economic activities in urban and semi-urban zones. Moreover, traditional water storage practices increase the breeding sites for Aedes aegypti, a primary vector of DF and DHF in Thailand. 6,7) Aedes aegypti, a daytime biting mosquito, is highly anthropophilic, often resides in and near human dwellings and preferentially feeds on humans. 1,8,9) This species has been found to be highly adapted to all man-made and natural environments and is a potential vector of dengue. [10][11][12] The key to preventing dengue transmission is to reduce human-vector contact using synthetic chemicals. [13][14][15][16][17] Several synthetic insecticides, including organochlorines, organophosphates, carbamates and synthetic pyrethroids, have been used in dengue control programs. 18) DDT (organochlorine) was widely used to control Ae. aegypti after the first dengue epidemic in 1958. 19,20) Deltamethrin (synthetic pyrethroids) is currently one of the most commonly used insecticides in public health programs and has been the mainstay for the emergency control of Ae. aegypti adults in Thailand since 1994. 18,21) Temephos (organophosphate) is commonly used in water containers for the control of Ae. aegypti larvae. Ultra-low-volume (ULV) applications of fenitrothion and malathion are used during the peak period of adult Aedes populations, especially during the rainy season. 16 (Received April 24, 2008; Accepted June 26, 2008) In this study, nine strains of Aedes aegypti mosquitoes from different localities in Thailand were subjected to susceptibility tests against commonly used insecticides for vector control in Thailand. Aedes aegypti from different localities were strongly resistant to DDT and permethrin, except for one strain from Chiang Mai (Chiang Mai-P) that was found to be susceptible to permethrin. In contrast, most Ae. aegypti strains are susceptible to deltamethrin and alphacypermethrin, except that Bangkok and Nonthaburi strains showed incipient resistance to deltamethrin and alphacypermethrin, respectively. Various levels of malathion and propoxur susceptibility were also detected in Ae. aegypti strains; however, two strains of Ae. aegypti (Satun and Nonthaburi) were found to be completely susceptible to malathion. The insecticide susceptibility level in three strains of Culex quinquefasciatus was also investigated. The results indicated strong resistance to DDT and moderate resistance to permethri...

Identifying the effective concentration for spatial repellency of the dengue vector Aedes aegypti

“…Given the THAI Ae. aegypti strain used in the current study have been characterized as DDT resistant [11], the lack of KD and mortality was not unexpected but instead strengthens the conclusion that a sublethal repellent mechanism was responsible for the reduction in mosquito entry rather than toxicity. Results also showed a difference in the median concentration of airborne DDT measured between the two treatment huts despite the fact that both received the same treatment.…”

A High Throughput Screening System for Determining the Three Actions of Insecticides Against <I>Aedes aegypti</I> (Diptera: Culicidae) Populations in Thailand

“…aegypti across Thailand have been found resistant to permethrin (Ponlawat et al 2005, Jirakanjanakit et al 2007). This apparent widespread resistance pattern could be related to the common use of commercial aerosol pest control products in many Thai households that contain permethrin or closely related synthetic pyrethroids and the wide distribution of pyrethroidimpregnated bed nets for mosquito control (Chareonviriyaphap et al 1999, Ponlawat et al 2005, Sathatriphop et al 2006, Thanispong et al 2008. Most strains were susceptible to ␣-cypermethrin with evidence of incipient resistance in the Nonthaburi strain and Songkhla in southern Thailand.…”

Host feeding responses of Aedes aegypti (L.) exposed to deltamethrin

“…Other methods to prevent dengue transmission are to reduce human‐vector contact using insecticides that attack the adult mosquito. Synthetic insecticides, particularly pyrethroids, have been used extensively (especially during high transmission periods or outbreaks) to control dengue vector mosquitoes in Thailand (Chareonviriyaphap et al 1999, Somboon et al 2003, Jirakanjanakit et al 2007, Thanispong et al 2008). In general, pyrethroids have been the insecticides of choice for many decades because of their high insecticidal activity, relatively low mammalian toxicity, rapid degradation in the environment, and relative lower cost compared to alternative class compounds.…”