Transmission thresholds and pupal/demographic surveys in Yogyakarta, Indonesia for developing a dengue control strategy based on targeting epidemiologically significant types of water-holding containers

All water-holding containers (ca. 3000) associated with approximately 320 residences in Yogyakarta, Indonesia, were examined for the presence of Aedes aegypti (L.), Aedes albopictus Skuse, and Culex quinquefasciatus Say pupae in four replicate surveys conducted during two dry seasons (1996 and 1998) and two wet seasons (1997 and 1999). Less than 6% of these receptacles had pupae. Ae. aegypti pupae collected were ten times more than Ae. albopictus (ca. 1600 vs. 160 respectively); Cx. quinquefasciatus was rarely encountered. From a dengue perspective, the epidemiological significance of a particular type of container is a function of the number of Ae. aegypti pupae per person – calculated simply as the ratio of total number of Ae. aegypti pupae recovered in that type and the number of residents, ca. 2800. Overall, there was an average of 0.57 Ae. aegypti pupae per person. Assuming an overall herd immunity of 33% and an average temperature of 29 °C, we estimate the transmission threshold in Yogyakarta to be approximately 0.43 Ae. aegypti pupae per person. By eliminating mosquito production in two common household containers – wells and used tyres the number of Ae. aegypti pupae would be reduced from 0.57 to 0.29 per person, below our estimate of the transmission threshold. An assessment of the effectiveness of this strategy is currently being conducted in a multi-year study in Yogyakarta using an insect growth regulator (IGR) for mosquito control.