The European gypsy moth (Lymantria dispar dispar) was detected in Washington in 1974. Since the early 1990s, another variety of gypsy moth, the Asian gypsy moth (L. dispar asiatica), has been intercepted multiple times by WSDA, often as egg masses attached to cargo on ships originating from Asian ports. Over the past 40 years, trapping and rapid response efforts have been successful in preventing permanent populations of either variety of gypsy moth in the PNW. In 2019, a closely related moth species known as the Hokkaido gypsy moth (L. umbrosa) was detected in Washington. In response, WSDA initiated an eradication program for the Hokkaido gypsy moth in spring of 2020.
Pest description and damage The wings of male gypsy moths are tan with a series of dark-brown wavy lines and relatively large, feathery antennae. The wingspan of the male moth is about 1.5 inches long. The female moths are larger, about 2-inch wingspan, but sport wings of a much lighter color—cream to white. The female moths of the European gypsy moth cannot fly, but the female Asian gypsy moth can fly and readily disperse. The moths are most active in summer. The more mature larvae have five pairs of distinctive blue dots followed by red dots along their back and can be found late spring to early summer. The larvae of both European and Asian gypsy moths feed on over 500 trees, shrubs, and plants including most hardwood and conifer trees found in the Pacific Northwest. In parts of northeastern US, this species defoliates entire forests. Homeowners should be on the lookout for the gypsy moth egg masses from late autumn to early spring as these are, by far, the most inadvertently transported stage of this pest. Each egg mass contains hundreds of round eggs covered with a dense mat of light tan hairs. These masses are usually laid on the bark of the host trees, but may be found on automobiles, RVs, firewood, doorframes, windowsills, furniture or just about any sheltered surface.
Pest monitoring Traps that rely on lures which release a sex pheromone to attract and monitor male moths are commercially available. WSDA places around 25,000 green or orange delta traps on host trees throughout the state each summer.
Management This is a quarantined pest species. If you suspect you have found plant damage, or any stage of this insect, please report the finding to the State Department of Agriculture or local university Extension office. When confirmed as a gypsy moth, these state agencies will respond and work to eradicate this pest as soon as possible. WSDA uses an IPM approach that will employ a range of biological, mechanical, cultural and chemical tactics to eradicate populations of gypsy moth.
For further information:
Crabo, L., R. Zach & M. Peterson. 2019. Pacific Northwest Moths. http://pnwmoths.biol.wwu.edu