Examination of a miniaturized funnel trap for Aedes aegypti (Diptera: Culicidae) larval sampling.

Funnel traps are often used to sample for the presence of Aedes aegypti (L.) (Diptera: Culicidae) larvae in subterranean aquatic habitats. These traps are generally > or = 15 cm in diameter, making them impractical for use in subterranean sites that have narrow (10-cm) access ports, such as those in standard-sized septic tanks. Recent research indicates septic tanks may be important habitats for Ae. aegypti in Puerto Rico and the Caribbean. To sample mosquito larval populations in these sites, a miniaturized funnel trap was necessary. This project describes the use of a smaller funnel trap for sampling larval populations. The effects of larval instar (third and fourth) and population density on trap efficacy also are examined. The trap detected larval presence 83% of the time at a larval density of 0.011 larvae per cm(2) and 100% of the time at densities > or = 0.022 larvae per cm(2). There was a significant trend of increasing percentage of recaptured larvae with higher larval population densities. Although the miniaturized funnel trap is less sensitive at detecting larval presence in low population densities, it may be useful for sampling aquatic environments with restricted access or shallow water, particularly in domestic septic tanks.

Septic tanks as larval habitats for the mosquitoes Aedes aegypti and Culex quinquefasciatus in Playa-Playita, Puerto Rico.

Adult Aedes aegypti (Linnaeus) (Diptera: Culicidae) were previously recovered from emergence traps on septic tanks in southeastern Puerto Rico. In this study we quantified immature mosquito abundance and its relationship with structural variables of the septic tanks and chemical properties of the water containing raw sewage. A miniaturized floating funnel trap was used to sample 89 septic tanks for larvae in the Puerto Rican community of Playa-Playita. Aedes aegypti larvae were recovered from 18% of the sampled tanks (10.3 larvae per septic tank per day). Larval presence was positively associated with cracking of the septic tank walls and uncovered access ports. Larval abundance was positively associated with cracking of the septic tank walls and larger tank surface areas, and inversely associated with the total dissolved solids (TDS). Culex quinquefasciatus (Say) larvae were also recovered from 74% of the septic tanks (129.6 larvae per septic tank per day). Larval presence was negatively associated with TDS in the water and larval abundance was positively associated with cracking of the septic tank walls. A screened, plastic emergence trap was used to sample 93 septic tanks within the community for Ae. aegypti and Cx. quinquefasciatus adults. Aedes aegypti adults were recovered from 49% of the sampled tanks (8.7 adults per septic tank per day) and Cx. quinquefasciatus adults were recovered from 97% of the sampled tanks (155.5 adults per septic tank per day). Aedes aegypti adult presence was positively associated with cracking, uncapped openings and septic water pH. The Ae. aegypti adult counts were positively associated with cracking and inversely associated with TDS and conductivity. This study marks the first published record of the recovery of Ae. aegypti larvae from holding tanks containing raw sewage in the Caribbean region. Our study indicates that Ae. aegypti larvae are present in sewage water and that septic tanks have at least the potential to maintain dengue transmission during the dry season.