A low-flying airplane that made several rounds over Edmonds and Woodway Friday morning was making  a pesticide application aimed at preventing the spread of invasive gypsy moths. The Washington State Department of Agriculture announced last month it would be spraying a 672-acre site in Woodway and a 639-acre site in Everett’s Boulevard Hills neighborhood.

The Hokkaido gypsy moths — native to Asia — arrived in Snohomish County forests last year. They feed on over 500 species of trees, including many conifers, and the trees that they defoliate often die.

Washington state has had more Asian gypsy moth introductions than any state in the U.S., the agriculture department says. They arrive as egg masses attached to ships carrying cargo from Asian ports.

The treatment consists of aerial applications of a soil bacteria called Bacillus thuringiensis var. kurstaki, or Btk, which is an insecticide approved for use in organic agriculture and in organic gardening. “It has an excellent safety record around people, plants, pets, fish, birds and bees and has been used globally for decades as a safe and effective treatment for combatting gypsy moth,” the agriculture department said on its website.