Finding Aedes aegypti Mosquitoes

For more details on invasive Aedes aegypti surveillance in San Mateo County, please visit our Aedes aegypti surveillance data section.

How does the District find something as small as an Aedes aegypti mosquito in an entire county?

District uses three kinds of traps to detect invasive mosquitoes in San Mateo County. Two of these traps attract female mosquitoes looking for a place to lay their eggs, while the third attracts female mosquitoes seeking a blood meal.


 Ovicups consist of a small plastic cup filled with tap water and a regular wooden tongue depressor wrapped in a coffee filter. This unlikely-sounding combination of ordinary materials is irresistible to container-breeding mosquitoes like Aedes aegypti, who are lured to the ovicup to lay their eggs on the wet coffee filter. Laboratory staff inspect the ovicups weekly for mosquito eggs and larvae, and identify them by species. Any eggs or larvae are then destroyed to prevent the emergence of adult mosquitoes.


 AGO traps consist of a bucket of water with a special lid containing a sticky surface. Female mosquitoes enter the trap to lay their eggs, then become stuck to the inside of the trap. Laboratory staff collect mosquitoes from AGO traps every other week and identify them by species. Since mosquitoes are unable to access the water in the trap, they cannot lay their eggs.


 The third kind of trap used to monitor for Aedes aegypti is called a BG Sentinel trap. Unlike ovicups and AGO traps, they attract female mosquitoes who are hoping to find a meal. BG Sentinel traps use dry ice to produce carbon dioxide vapor, which mimics human exhalation. They also contain a special chemical that smells like a human to the mosquito. When female mosquitoes approach to bite, they are sucked into a collection bag by a tiny fan. These traps are deployed overnight, and laboratory staff retrieve mosquitoes from the trap the next day and identify them by species.

In addition to trapping mosquitoes, the District laboratory identifies mosquito larvae and eggs collected by technicians during property inspections. Many of the Aedes aegypti larvae detected during 2014 and 2015 were found during property inspections, highlighting the need for residents to eliminate even small sources of standing water on their property.