Deltamethrin Susceptibility Status of Aedes aegypti and Culex quinquefasciatus in City of Phuket - ความไวของยุงลายบ้านและยุงรำคาญ ต่อสารเดลต้ามิทรินในเขตเทศบาลนครภูเก็ต

Mosquito spray with 0.05% deltamethrin had been carried out continuously within the City of Phuket following the rising of Dengue hemorrhagic fever incidence with the possibility of inducing the risk of mosquito’s tolerance. This study was aimed to assess the susceptibility of Aedes aegypti and Culex quinquefasciatus against 0.05% deltamethrin spray at 5 temples in the City of Phuket and to determine the knock down time for 50 mosquitoes out of 100 mosquitoes (KDT50) according to the WHO standard 1981&1998. Frequency and mean were used for data analyzing.The result revealed that Ae. aegypti either from outside or inside the buildings and Cx. quinquefasciatus within the City of Phuket were susceptible to 0.05% deltamethrin, while the mean KDT50 of Culex spp. were higher than those Ae. aegypti either from outside or inside the buildings as well as Ae. aegypti Bora strain (Aedes spp. that susceptible to the insecticide) at 2.8, 3.0, and 7.2 folds repectively. Even though Ae. aegypti and Cx. quinquefasciatus still susceptible to 0.05% deltamethrin, the study revealed that the Cx. quinquefasciatus began to develop incipient resistance as compare to Bora. Therefore, we should be aware and use the insecticide appropriately. Periodic sensitivity test of 0.05% deltamethrin against the mosquito should be conducted to prevent or slow down the risk of inducing chemical resistance among mosquito vectors. Key words: mosquito resistant, Dengue hemorrhagic fever, Aedes aegypti, Culex quinquefasciatus