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The hypothesis tested was that most pupae of Aedes aegypti are produced in a few types of containers so that vector control efforts could concentrate on eliminating the most productive ones and thus prevent dengue outbreaks. Pupal surveys were conducted twice in 2004 in an urban area in southern Puerto Rico. A total 35,030 immature mosquitoes (III and IV instars, pupae) was counted in 1,367 containers found with water in 624 premises during the first survey. Only pupae were counted in the second survey in 829 premises, 257 of which had containers with water, and 124 contained Ae. aegypti pupae (15%, 22% in the first survey). We found fewer (583) containers with water than in the first survey, but 202 had pupae (35%; 18.5% in first survey). Containers yielded 3,189 Ae. aegypti pupae, which was slightly fewer than those found in the first survey (3,388 pupae). The hypothesis was supported by the data, showing that 7 of 18 types of containers contained 80% of all female pupae. The most productive containers generally were also common. We used several criteria (i.e., container use, two-step cluster analysis based on environmental variables of containers and premises) to classify the containers and premises and to evaluate pupal distribution at various spatial scales (container, premise, and residences versus public areas). Most pupae were in 4 of 10 types of container usage categories. The cluster technique showed that most pupae were in unattended, rain-filled containers in the yards, particularly in receptacles in the shade of trees that received rainfall through foliage and had lower water temperatures. Pupal counts were adjusted to a negative binomial distribution, confirming their highly aggregated dispersal pattern. Cluster analysis showed that 61.3% of female pupae were in 40 (6.4%) of 624 premises that had in common their larger yards, number of trees, and container water volume. Using number of Ae. aegypti larvae, Breteau Index, or the presence of immature forms as indicators of pupal productivity is not as efficient in identifying the most productive types of containers as direct pupal counts.
Received August 1, 2005. Accepted for publication September 4, 2005.
Acknowledgments: We thank Gilberto Felix, Ariana Muñoz, José Aponte, Khristian Pizarro, Abraham Rivera, Alejandro Rodríguez, and José Torres for their laboratory and field assistance, and Marcos Rodríguez for his help with the identification of the tree species. We also thank the Municipality of Salinas and Centro de Recaudación de Impuestos Municipales for providing maps of the study area.
Financial support: This study was partly supported by the Tropical Disease Research Council (Tropical Disease Research/World Health Organization) (OD/TS-03-00523) and the Centers for Disease Control and Prevention.
* Address correspondence to Roberto Barrera, Dengue Branch, Centers for Disease Control and Prevention, 1324 Calle Cañada, San Juan, PR 00920. E-mail: rbarrera{at}cdc.gov
Authors’ address: Roberto Barrera, Manuel Amador, and Gary G. Clark, Dengue Branch, Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention, 1324 Calle Cañada, San Juan, PR 00920, Telephone: 787-706-2399, Fax: 787-706-2496, E-mails: rbarrera{at}cdc.gov, mamador{at}cdc.gov, and gclark{at}cdc.gov.
Reprint requests: Roberto Barrera, Dengue Branch, Centers for Disease Control and Prevention, 1324 Calle Cañada, San Juan, PR 00920, E-mail: rbarrera{at}cdc.gov.
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