SILVER LAKE — The Washington State Department of Agriculture has begun treatments for the eradication of gypsy moths in the Silver Lake area of Cowlitz County.

WSDA planned to send an airplane to spray about 640 acres using a soil bacteria called Btk. It was the only planned action against the gypsy moth pest this year, the agency stated.

Gypsy moths are established in 20 states in the Midwest and Northeast U.S., where millions of acres of trees have been defoliated in forest and urban areas. The moths feed on over 500 types of plants, trees and shrubs.

So far, the moths have not become permanently established in Washington.

The bacteria the agency employs to eradicate the moths is naturally occurring and commonly found in soil and on plants around the world. It has been used as a biological insecticide for gypsy moths since the 1970s, according to WSDA. It poses a very low risk to humans, impacting caterpillars while not harming insects that are beneficial to the environment, such as lady beetles, parasitic wasps, ants or bees. Birds, fish and other animals are also not affected.

Btk is applied aerially during April and May. Each year, WSDA picks a location for application. Current and past locations can be viewed on the WSDA website.

For the past 40 years, the WSDA has been successfully trapping gypsy moths. If the moths were to get established in the state, forest products and horticulture would be subject to quarantine restrictions. Homeowners would also have to increase their use of pesticides.

For more information, visit agr.wa.gov.