MCHD Environmental Health Section Vector Control

Environmental Health Section -
Vector and Nuisance Control
5235 N. Columbia Blvd.
Portland, OR 97203
(503) 988-3464
Email: vector.nuisance@co.multnomah.or.us

West Nile Virus Information

Mosquito Control
Multnomah County Vector and Nuisance Control is responsible for controlling mosquitoes throughout Multnomah County by means of an integrated program. This holistic approach uses multiple complimentary methods such as identification of insect or animal species of concern, prevention, surveillance, treatment and education. For more details see our Mission Statement. We depend upon the public to control “backyard” mosquito problems and alert us to larger problems. If you have any questions or would like to submit a mosquito complaint call our office at (503) 988-3464, or Email us at vector.nuisance@co.multnomah.or.us.
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In a Mosquito's Life:

1. Adult Mosquitoes are a problem because the females require blood to lay their eggs. This affinity for blood gives mosquitoes the potential to transmit disease.
2. Mosquito eggs laid by each female can number in the hundreds. Eggs can be laid in the soil of temporarily flooded areas such as floodplains or on the water's surface.



4. Mosquito Pupae are the last stage before mosquitoes become flying, biting adults. Pupae also require a constant water source and at least a day to mature. 3. Mosquito Larvae require a constant water source to mature. If the weather is warm they can mature from egg to pupae in less than a week.

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Controlling Backyard Mosquitoes:

Keep all buckets and cans of water empty and change the water in wading pools every other day.
Keep swimming pools maintained properly by proper chlorination and working equipment.
Keep rain gutters cleared of debris.
Keep vegetation in and around ornamental ponds thinned and minimize mosquito production by adding mosquito fish.

Did you know... A coffee can with an inch of water can produce over a thousand mosquitoes every 7 days!
Help eliminate the West Nile Virus! Use our web form to report standing water.
Downloadable documents on mosquito control (PDF documents):

Posters on reducing mosquito breeding sources:

In English
In Russian
In Spanish
In Korean
In Chinese
In Vietnamese

Are you raising mosquitoes in your backyard? See downloadable brochure (PDF), below

In English
In Russian
In Spanish
In Korean
In Chinese
In Vietnamese

2004 Mosquito Complaints
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Mosquito Surveillance

In Multnomah County, mosquito surveillance is conducted using carbon dioxide (CO2) baited traps like the one, pictured on the left. CO2 traps are used to collect adult mosquitoes. The mosquitoes are all counted and identified to determine the levels of local populations. Some of the mosquitoes are then tested for the presence of mosquito-borne diseases such as West Nile Virus (WNV).

On the other hand, mosquito larvae are collected using dippers, like the one shown right. We always check a site before it is treated. We look to ensure that the larvae we find are a species that impact people. One mosquito larva in a dipper is equivalent to one million mosquitoes per surface acre of water.

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Mosquitoes Commonly Found In Multnomah County

Aedes
Ae. cinereus
Ae. vexans

Culiseta

Cs. incidens
Cs. inornata
Cs. minnesotae
Cs. particeps

Anopheles
An. freeborni
An. punctipennis
Ochlerotatus (formerly Aedes)
Oc. sierrensis
Oc. sticticus
Oc. increpitus/washinoi complex

Coquillettidia
Cq. perturbans

Culex
Cx. boharti
Cx. pipiens
Cx. stigmatosoma
Cx. tarsalis
Cx. territans

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Alien Invaders! - Exotic Mosquitoes Found in Multnomah County

In Spring 2006, Multnomah County Vector Control first found the non-native Japanese or Rock Pool mosquito, Ochlerotatus japonicus in Multnomah County. This Asian species is generally found in Japan, Korea, Taiwan, and South China. It is unknown how this species arrived in Multnomah County but the movement of waste tires or freight is suspect. This species was first detected in 1998 in New York and New Jersey and since found in Ohio, Maryland, Connecticut, Massachusetts, Pennsylvania, Virginia and Washington. This invasive species is of public health concern for its capacity to transmit West Nile virus and Japanese encephalitis. Multnomah County Health Department, Vector Control has been diligently tracking this mosquito since 2006 and to date, not further mosquitoes have been detected. Multnomah County, State of Oregon and the Washington State Department of Health, Zoonotic Disease Program are working together to track and share information on this alien invader. For more information including a map of where this mosquito has been found in Oregon and Washington see documents below.

Informational documents about Ochlerotatus japonicus:

Activity map May 24, 2007 - May 29, 2007

Japonicus map - Multnomah County 06-01-07

Media release re: Japonicus, May 2006

Japonicus found in Multnomah County - 2006 (narrative)

Larval Mosquito Control
Multnomah County Vector and Nuisance Control focuses its mosquito control program on the larval stages, or immature stages, of mosquitoes. Our goal is to target mosquitoes before they become flying, biting adults. This involves locating where the larvae are and applying larvicides (a larvae killer) for control. We routinely check thousands of sites each year and treat 3,000 to 4,000 acres annually. The most numerous mosquitoes in our area are floodwater mosquitoes that breed in the floodplains of the Willamette and Columbia Rivers.

Map of Known Mosquito Larvae Production Sites (PDF)

Map of Stormwater Sites (PDF)

Floodwater mosquitoes are aggressive biters capable of flying up to 20 miles from their birth site in search of blood. In the spring of 2000, Multnomah County Vector and Nuisance Control began using a helicopter to treat the floodplains.

The success of the program is due to the cooperation between Multnomah County Vector and Nuisance Control and other mosquito control programs in Columbia, Clark and Cowlitz Counties. By using an aerial application of larvicide, we were able to treat more acreage in less time, overall providing a better treatment.

For more information on our larviciding program or to report a potential breeding source call Multnomah County Vector Control at (503) 988 – 3464 or E-mail us at vector.nuisance@co.multnomah.or.us. Or submit a standing water report form online.

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Adult Mosquito Control

Adulticides are an important tool for mosquito control when reduction of adult mosquitoes is necessary in the event of a health emergency crisis. These products are considered for use when no other control methods are optimal. This is done for several reasons:

Adulticides are broad-spectrum materials, which means they may affect other insect populations other than just mosquitoes. By not using them on a regular basis, limits the impact our mosquito control work has on the environment.
It is easier to control mosquitoes when they are found condensed in water as larvae than as adults.

To view the guidelines for adult mosquito control in the absence of West Nile virus, see Mosquito Control Guidelines Absence of WNV.

For more information in a downloadable document,
see "Controlling Adult Mosquitoes" (PDF), below:

In English

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Environmental Health Section | Health Department | Multnomah County

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The address for this site is: http://www.mchealth.org/vector/mosq.htm
Created: February 15, 2001
Revised September 22, 2004
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