In Thailand, controlling mosquitoes at their immature stages has been central to their dengue control programme (Chunsuttiwat and Wasakarawa, 1994). Productive larval sites in Thailand are stored water containers in and around houses. Aedes aegypti, the most important vector, exploits domestic artificial water-holding containers as its breeding sites. In northeast Thailand, built-in cement containers holding water for bathing or flushing toilets are the most productive breeding sites (Chau et al., 2001). The dengue control program has focused on promoting householder responsibility for reducing the number of breeding sites, or treating essential water-holding containers with larvicide, or placing fish in water containers or covering them with lids to prevent mosquito oviposition or cleaning water containers weekly; as newly hatched larvae require approximately 9 days to develop to the adult stage, weekly emptying of containers will prevent emergence of adult mosquitoes. The larvicide temephos is distributed free to households for mosquito control.