Response of malaria vectors to conventional insecticides in the southern districts of Odisha State, India.

BACKGROUND & OBJECTIVES: Updating information on response (susceptible / resistant status) of vectors to the insecticides in use is essential to formulate and introduce appropriate resistance management strategy. Therefore, a study was undertaken in the 10 southern districts of Odisha State, which are endemic for Plasmodium falciparum malaria, to determine the insecticide susceptibility/ resistance status of Anopheles fluviatilis and An. culicifacies, the vectors of malaria. METHODS: Mosquitoes were collected during September 2010 - February 2012 from 60 randomly selected villages in the 10 districts and blood-fed females were exposed to the diagnostic dosage of DDT (4.0%), malathion (5.0%) and deltamethrin (0.05%) for one hour. Mortality was recorded at 24 h after the exposure. The test mortality was corrected to the control mortality. RESULTS: An. fluviatilis was susceptible to the three insecticides tested while, An. culicifacies was resistant to DDT and malathion in all the 10 districts except in two, where its response against malathion was under 'verification required' category. Against deltamethrin, An. culicifacies was susceptible in two districts; while in the other eight districts its response was under 'verification required' category. INTERPRETATION & CONCLUSIONS: Since An. fluviatilis the vector species primarily associated with transmission of malaria, was still susceptible to DDT, indoor residual spraying with DDT could be continued in the 10 districts. Also, in view of the large scale implementation of long lasting insecticidal nets and the signs of development of resistance in An. culicifacies to deltamethrin, response of the vectors to synthetic pyrethroids needs to be periodically monitored.