How We Control Mosquitoes

Multnomah County keeps our community safe and livable by using an approach called integrated mosquito management to control mosquitoes. This approach is designed to keep mosquito populations at a safe level, not eliminate them. It focuses on preventing mosquitoes through these activities:

• Monitoring mosquito populations helps us to identify changes in our community such as geographic spread of vector mosquitoes.
• Preventing or controlling ideal breeding habitat. Different mosquitoes prefer different habitats. We work to identify what those habitats are and work with landowners and community members to eliminate mosquito breeding conditions when possible.
• Controlling mosquitoes as larvae prevents mosquitoes from becoming flying and biting adult insects.

We have three program areas:

Surveillance

Surveillance, or monitoring mosquitoes happens in the lab and in the field.

• Field monitoring helps us to identify where and how many mosquitoes are living in our communities. Adult mosquitoes are collected using a variety of methods. Staff also perform extensive larval sampling in aquatic environments.
• Lab monitoring helps us to determine exactly what type of mosquitoes are living in our community. Adult and immature mosquitoes are collected, counted and identified to determine the levels of and species diversity of local populations. Some species of adult mosquitoes are tested for the presence of mosquito-borne diseases such as West Nile virus.
• Dead bird collection (specifically corvids such as crows, jays and their kin) for West Nile virus monitoring between May 15 and September 30.

Education

Understanding mosquitoes is the first step in preventing them. We offer a variety of educational opportunities focused on neighborhood-level prevention of mosquitoes. Please contact us to learn more.

Control

We prioritize immature mosquito control before they become flying, biting adults. Usually this means applying BTi (a soil bacteria found throughout our environment) into habitats with excess mosquito populations.

BTi works by disabling the stomach enzymes in mosquito larvae, which prevents them from developing into adult mosquitoes. BTi is not known to affect other aquatic biota.

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