OLYMPIA — With the press the Asian giant hornet has gotten this year, it’s easy to forget it’s only one of a number of invasive pests the Washington State Department of Agriculture battles every day.

According to WSDA spokesperson Karla Salp, entomologists have been busy battling the gypsy moth — both the Asian and European variants — very successfully for the last 40 years.

In fact, next spring sometime, the WSDA is going to spray around 639 acres near Silver Lake in Cowlitz County with a bacteria, Bacillus thuringiensis var. kurstaki, or Btk, as part of its ongoing efforts to ensure the Asian gypsy moth does not establish a foothold in Washington state.

The bacterium itself produces a protein that’s lethal to gypsy moth caterpillars as they munch on bacteria-coated leaves. Btk is such a successful natural pesticide that genes from the bacteria have been inserted into some types of corn, cotton, potatoes and tobacco, giving the plants limited ability to resist insect pests on their own.

“Btk is used in a lot of type of applications,” Salp said. “It’s one of the most commonly used pesticides in organic agriculture.”

Btk is safe for bees and pets, Salp said, but cars parked outside in the application area can get sticky.

Gypsy moth caterpillars feed on hundreds of trees and shrubs, often killing these plants in neighborhoods, parks, and forests. The pest also destroys wildlife habitat and some people are allergic to the caterpillars. An infestation can also trigger costly quarantines for timber, Christmas trees, and other forest and nursery products.

Salp said the European gypsy moth was brought to the United States more than a century ago in an attempt to kick-start a domestic silk production industry. Some of the moths escaped, as pests are wont to at times, and have so far spread to 20 states in the Eastern United States.

Controlling the European gypsy moth is fairly easy, Salp explained, given that the females can’t fly and males don’t stray far from the females.

However, Asian gypsy moth females can fly, and combined with their far broader diet — they eat roughly 500 different species of plants, as opposed to the 300 preferred by their European cousins — including evergreen trees, which don’t have the same ability to survive moth attacks that deciduous trees do because they are able to shed their leaves in autumn.

“When an evergreen tree is defoliated, it will not put out new needles,” she said.

Salp said the WSDA sets about 20,000 traps annually, and so far, neither species of gypsy moth has established itself in Washington.

The treatment will be timed to hit the caterpillars as they are small — one-quarter inch to one-half inch long — but very hungry, so they can ingest as many bacteria as possible.

“It’s based on degree days and when the oak leaves are 40% emerged or so,” she said. “I’ve been doing this for five years, and it’s happened anywhere from the beginning of April to the middle of June. It just depends on the local climate.”

Prior to next spring’s spraying, however, WSDA will conduct two environmental reviews, consult with local, state and federal agencies and engage in a public outreach that includes a virtual informational open house. Residents in or near the proposed treatment area will also receive postcards notifying them of the proposal.

While Salp said the WSDA tends to focus its anti-gypsy moth efforts west of the Cascades, the moth could find a nice home in parts of Eastern Washington, especially Spokane and the northeast corner of the state.

“Cold is not an issue, but there may be heat issues (in the Columbia Basin),” she said. “The warmer it gets, it tends not to fare quite as well.”

Charles H. Featherstone can be reached at [email protected].