State to treat outbreak of gypsy moth in Tukwila this spring, summer

  - Washington state Department of Agriculture
— image credit: Washington state Department of Agriculture

The Washington State Department of Agriculture  has announced  a proposal to treat about 180 acres in Tukwila and Renton this spring and summer to eliminate an introduction of the destructive European gypsy moth.

Many of the moths were trapped near Interurban Avenue South and South 149th Street, an area that includes light industry, a few apartment complexes, some houses and an extensive greenbelt.

During last summer’s annual statewide trapping program, WSDA trappers caught 27 gypsy moths, including 25 in Tukwila. Entomologists also discovered 11 gypsy moth egg masses in Tukwila, indicating that a reproducing population is present. Between 500 and 1,000 gypsy moth caterpillars can emerge from a single egg mass.

“The large number of catches in Tukwila is one of the largest we have seen in recent years,” Jim Marra, managing entomologist for WSDA said. “Gypsy moth has defoliated millions of acres of forest in recent years across the Northeast and Midwest. If left unchecked, gypsy moths would devastate Washington’s forests.”

WSDA is proposing a two-step response to the detected gypsy moth population: eliminate gypsy moth caterpillars with ground-based treatments using a biological insecticide on trees and shrubs in the area around the

egg mass locations. This would be followed later by an aerial application of an agent that disrupts mating behavior in any remaining adult gypsy moths.

WSDA entomologists would treat about 10 acres at the center of the gypsy moth population from the ground beginning in late April or early May using Bacillus thuringiensis kurstaki (Btk). Between three to five applications would be performed seven to 10 days apart. Btk is a naturally occurring soil bacterium registered by the U.S. Environmental Protection Agency (EPA). It affects only caterpillars and has been used for decades to control gypsy moth.

To affect any adult gypsy moths present, WSDA would treat the entire 180-acre area in July by aircraft, releasing tiny, confetti-sized, pheromone-impregnated flakes. The synthetic flakes confuse male gypsy moths so

they cannot locate female moths to mate with—effectively stopping an infestation—in a process entomologists call “mating disruption.”

WSDA proposes to use disparlure (also known by the trade name Disrupt II), a synthesized version of the pheromone or sex attractant emitted by the female gypsy moth to attract the male. Mating disruption is a strategy

that has been used successfully in other states, though it is the first time it is being tried in Washington for gypsy moth.

Mating disruption with disparlure offers several benefits, including:

• Less expensive than other treatment options

• Targets a specific species, in this case, gypsy moth

• Treatment can be accomplished in a single, 30-minute aerial flight.

Residents in the proposed treatment area will receive information and can attend a community open house in Tukwila. The time and location of the open house will be announced later.

Gypsy moth has been detected in Washington every year since 1977, but permanent populations have not been established because of the state’s aggressive trapping and eradication programs. Statewide, trappers

placed 19,000 small cardboard traps last summer to make sure the non-native gypsy moth hasn’t been introduced in other locations.

Gypsy moth feeds on more than 500 species of trees and plants and reproduces very rapidly. Visit for more information on WSDA’s gypsy moth program  or call

the WSDA gypsy moth toll-free hotline at 1-800-443-6684.

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