Seasonality and insecticide susceptibility of dengue vectors: an ovitrap based survey in a residential area of northern Sri Lanka.

With the backdrop of a high incidence of dengue in Jaffna District, Sri Lanka, an ovitrap based survey was carried out from May 2005 to April 2006 in a residential area to study the seasonality and insecticide susceptibility of Aedes aegypti and Ae. albopictus. Conventional ovitraps were placed inside and outside of 10 randomly selected houses to collect indoor breeding and outdoor breeding Aedes mosquitoes; collections took place fortnightly. A total of 3075 Ae. aegypti and 2665 Ae. albopictus were collected in outdoor ovitraps, whereas in indoor ovitraps a total of 2528 Ae. aegypti and 2002 Ae. albopictus were collected. The highest values for Aedes density and positive ovitrap percentage were recorded in January 2006. A seasonal shift was observed in the density of Ae. aegypti and Ae. albopictus. Ae aegypti density was high during and after the Northeast monsoon whilst Ae. albopictus was the dominant species during the onset of the Northeast monsoon. A significant association (p < 0.05) between Aedes density and rainfall was observed. The association of these two species to site, either indoors or outdoors, was not statistically significant (p > 0.05). Both the species were found to be highly resistant to 4% DDT and completely susceptible to 5% malathion. The high prevalence and the ability of both species to breed indoors and outdoors should be taken into account when formulating a dengue vector control program with community participation in the Jaffna District, Sri Lanka.