Dengue Bulletin – Volume 31, 2007 141 Development sites of Aedes aegypti and Ae. albopictus in Nakhon Si Thammarat, Thailand S. Wongkoon, M. Jaroensutasinee   , K. Jaroensutasinee and W. Preechaporn Computational Science Graduate Programme, School of Science, Walailak University, Thasala, Nakhon Si Thammarat 80161, Thailand Abstract This study investigated how the seasons affect the development sites of Aedes larvae in three topographical areas: mangrove, rice paddy fields and mountainous areas. We examined how the number of Aedes larvae varied in different types of water containers. Water containers were categorized into the following groups: indoor/outdoor containers, artificial/natural containers, earthen/plastic containers, containers with/without lids and dark/light-coloured containers. Samples were collected from 300 households in both the wet and dry seasons from three topographical areas in Nakhon Si Thammarat province with 100 households per topographical area. The results showed that in the wet season, there were higher numbers of Ae. aegypti and Ae. albopictus larvae than in the dry season. Moreover, the number of Ae. albopictus larvae was higher in mountainous areas than in mangrove and rice paddy areas, in both the wet and dry seasons. The number of positive containers was higher in outdoor containers than in indoor containers, higher in artificial containers than natural containers, higher in earthen containers than plastic containers, higher in containers without lids than containers with lids, and higher in the dark-coloured containers than light-coloured containers in the three topographical areas in both wet and dry seasons. The number of positive earthen containers was higher in mangrove areas than in rice paddy and mountainous areas. The number of positive plastic containers was higher in rice paddy areas than mountainous and mangrove areas. Keywords: Aedes larvae; Season; Topography; Larval development site.  E-mail: jmullica@wu.ac.th Introduction Dengue fever is caused by dengue viruses of the family Flaviviridae, transmitted principally by Aedes aegypti, and, possibly Ae. albopictus, in the tropical and subtropical regions of the world. [1,2] Two clinical features, namely, dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) may lead to death. [3,4] No effective vaccine or chemotherapy is currently available for the prevention or treatment of dengue fever; therefore, prevention and control of the disease depend on vector surveillance and control measures. [5] Transmission cycles of the dengue virus depend on the interrelationship between the virus and its mosquito vector, which is influenced by environmental conditions. [6] Adult female Aedes mosquitoes acquire the dengue virus by biting infected humans during the viremic phase, which usually lasts for 4–5 days, although it may last up to 12 days. The virus is transmitted