Spatial distribution and insecticide susceptibility status of Aedes aegypti and Aedes albopictus in dengue affected urban areas of Rawalpindi, Pakistan.

BACKGROUND & OBJECTIVES: Dengue is one of the most common arthropod-borne viral diseases which is transmitted mainly by two vector species, Aedes aegypti (Linnaeus 1762) and Ae. albopictus (Skuse, 1894) worldwide. As there is no effective medicine and vaccine available, vector control remains the most effective measure to prevent its transmission and outbreak. The aim of the study was to confirm the co-occurrence of Aedes aegypti and Ae. albopictus populations in the different localities of Rawalpindi, Pakistan and examine their susceptibility status against different groups of insecticides.

METHODS: Ovitraps were randomly placed in the study localities. The number of eggs from all the ovitraps were counted and incubated for hatching in Medical Entomology and Disease Vector Control (MEDVC) insectarium for rearing up to adult stage. The adults were then identified by using the pictorial keys. Spatial distribution and aggregation of both Ae. aegypti and Ae. albopictus populations was determined by using Index of dispersion or variance to mean ratio and k values of the negative binomial distribution. The susceptibility status of both the species against different insecticides was assessed by using the World Health Organization (WHO) standard bioassay tests.

RESULTS: The results showed that there was coexistence among Ae. aegypti and Ae. albopictus populations and the aggregation of their eggs was also observed in all the localities studied in Rawalpindi. Larval bioassays of both the populations exhibited incipient resistance against temephos while adult susceptibility testing results showed that both the species were resistant to DDT, malathion, bendiocarb and permethrin.

INTERPRETATION & CONCLUSION: The results suggested that all the field populations of Ae. aegypti and Ae. albopictus existed together and showed qualitative changes in their susceptibility status. Resistance against deltamethrin and lambdacyhalothrin was not confirmed and further investigation was recommended to confirm the change in their susceptibility status. This study could help public health authorities to apply simultaneous control activities on both species due to their coexistence and also resistance management strategies should be formulated to slow down the process of development of resistance.