How We Control Mosquitoes

Multnomah County uses an approach called integrated mosquito management to control mosquitoes. It's designed to keep mosquito populations at a safe level, not eliminate them.

Mosquito control keeps our community safe and livable.

Did you find one of our mosquito traps?

mosquito trap

These traps use carbon dioxide gas from dry ice to attract adult mosquitoes, which are then trapped in a net with a small fan. They're left in place for less than 24 hours. If you see one, don’t worry—we'll remove it soon.

How We Work

• Monitor mosquito populations to identify changes, such as geographic spread of vector mosquitoes.
• Prevent or control ideal breeding habitat. Different mosquitoes prefer different habitats. We work to identify those habitats, and work with landowners and community members to eliminate mosquito breeding conditions when possible.
• Control mosquitoes as larvae to prevent them from becoming flying and biting adult insects.

Program Areas

Surveillance

• Field monitoring - To identify where and how many mosquitoes are living in our communities. Adult mosquitoes are collected using a variety of methods. We also perform extensive larval sampling in aquatic environments.
• Lab monitoring - To identify what species of mosquitoes live in our community. We also test for the presence of mosquito-borne diseases such as West Nile virus.
• Dead bird collection (Crows, jays and other corvids) between May 15 and September 30 to monitor for West Nile virus. 

Education

We offer a variety of educational opportunities focused on preventing mosquitoes in neighborhoods. Contact us at vector.nuisance@multco.us to learn more.

Control

We prioritize the control of immature mosquitoes before they become flying, biting adults. Usually this means applying BTi into habitats with excess mosquito populations.

BTi is a soil bacteria found throughout our environment. It disables stomach enzymes in mosquito larvae, which keeps them from developing into adults. BTi is not known to affect other aquatic biota.

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