Insecticide resistance in adult aedes mosquitoes

In a response to mosquito-borne disease such as dengue outbreak from time to time, the susceptibility of Aedes mosquitoes was assessed to identify the 50% knockdown time (KT50) of adult /Aedes mosquitoes to malathion insecticide. The KT50 value was applied to determine the insecticide resistance ratio by comparing field strain with laboratory susceptible strain. World Health Organization (WHO) standard procedure was used namely adult bioassay using WHO Diagnostic Test Kit to determine the resistance ratio based on the knockdown time (KT) of wild strain to laboratory susceptible strain. The /Aedes mosquitoes were bred from larval collected from two localities which are Shah Alam and Bangsar. About 300 samples were exposed to malathion insecticide impregnated paper for one hour. Knockdown mosquitoes were recorded each five minutes in one hour exposure. Mortality number was count after 24 hours. The laboratory susceptible strain from Vector Control Research Unit (VCRU), USM was used as a susceptible strain for comparison purpose in determination of resistance ratio. The adult bioassay test was carried out by using diagnostic dosages of 5.0% malathion. All bioassay results were subjected to probit analysis. The results exhibited the wild strain mosquitoes from Shah Alam shown a possibility of potency to insecticide resistance where the resistance ratio is 2.2 with 95% mortality. In contrast, wild strains from Bangsar were believed to develop insecticide resistance based on resistance ratio value 2.4 with 78% mortality. Thus, the present used of malathion with concentration 0.03 were not effective in killing the adult Aedes mosquitoes.