Assess the prevalence and insecticide resistance of major dengue vectors Aedes SP. in selected locations of Batticaloa District

Dengue has become the major vector borne disease in Sri Lanka. Control of the vectors Ae.aegypti and Ae.albopictus through elimination of breeding habitats and application of insecticides are considered as the most effective ways to suppress the dengue epidemic. The mosquito larval survey was undertaken in three MOH areas such as Oddamavadi, Eravur, and Vantharumoolai, during the period in between January to March and September to October, 2020 in Batticaloa district. Five areas in each MOH area were selected randomly for the survey. Larval indices such as House index (HI), container index (CI) and Breteau index (BI) were calculated by using standard WHO guidelines in order to find the dengue epidemic risk. Resistance status of dengue vectors to four commonly used insecticides such as DDT, malathion, deltamethrin and carbamate were also assessed by using standard World Health Organization (WHO) procedures. Findings of the container survey and larval survey revealed that the three study locations are abundant with wet containers that are potential for the dengue mosquito breeding. There was a significant difference (p=0.001) in the abundance of indoor containers in all three locations whilst there is no significant difference (p=0.697) in the abundance of outdoor containers in all three locations. The results also indicated that both species can breed in urban, suburban, and rural areas. But Ae.albopictus prefers mostly rural and outdoor premises where there is dense vegetation. Ae.aegypti was the dominant species in all three locations. The larval indices have showed that Oddamavadi and Eravur were at high dengue epidemic risk and Vantharumoolai was at moderate risk. Results of insecticide bioassay revealed that both of the species were susceptible to deltamethrin and both were resistance to DDT and carbamate. It has also been found that both of the species were possibly resistance to malathion. From this result we can conclude that deltamethrin can be effectively used for space spraying programmes during the outbreak of Dengue in Sri Lanka.