New pests making their homes in Pacific Northwest forests

In a time of world trade and global movement of people, hitchhiking insects are becoming more common. In the past 20 years, almost 60 exotic insect species have become established in Washington state. Some of these hitchhikers have, or may soon, become serious pests. While many of these pests do not attack trees, they can seriously degrade the quality of habitat for wildlife in our forests and fields.

Here is a small sampling of the imported insects that are posing the biggest threats in the Pacific Northwest:

Viburnum leaf beetle

Viburnum leaf beetle larvae.
Viburnum leaf beetle larvae. Photo: T. Murray/Washington State University

The viburnum leaf beetle (Pyrrhalta viburni) has been detected in Whatcom King and Snohomish counties. A native viburnum, the high bush cranberry — actually, a close cousin of the elderberry — is especially susceptible to attack. Many types of wildlife rely on high bush cranberry for a reliable food source.

For those growing high bush cranberry the labor intensive process of manually removing larvae can significantly reduce plant damage. Applying a sticky barrier to the base of bush stems will trap migrating mature larvae as they move to the soil in late spring. Learn more about the beetle and find insecticide and other control recommendations on the Washington State University (WSU) Extension website

Lily leaf beetle

Lily leaf beetle adult.
Lily leaf beetle adult. Photo: E. LaGasa/Washington State Dept. of Agriculture

Another recent invasive is the lily leaf beetle (Lilioceris lilii). While observations of this bright red beetle remain confined to the Bellevue, Seattle and Issaquah areas, the lily leaf beetle is a threat to two key native plants of the Pacific Northwest: the tiger lily (Lilium columbianum) and the chocolate lily (Fritillaria lanceolate). Handpicking and discarding of adult beetles, eggs, and developing larvae from leaves is a recommended control; effective insecticides have not been studied in Wash­ington state. Find more information in this document from the WSU Hortsense website.

Azalea lace bug

Azalea lace bug adult
Azalea lace bug adult. Photo: T. Shanan/Oregon Dept. of Agriculture

The azalea lace bug (Stephanitis pyrioides)  was first discovered in King County, in 2008. The following year, it was identified in Oregon. Azalea lace bugs cause significant damage and mortality to azaleas and rhododendrons. Damage also has been observed on huckleberry, salal and other native plant species. A factsheet from the Oregon State University Extension Service describes the various approaches to controlling damage caused by this invasive from Japan.

Spotted winged drosophila

Spotted wing drosophila.
Spotted wing drosophila. Photo: E. LaGasa/ Washington State Dept. of Agriculture

First detected in Seattle in 2009 shortly after it was detected in California, the spotted winged drosophila (Drosophila suzukii) is a significant new pest to many small fruits. With its high reproductive capacity and fast generation time this form of fruit fly has had a major impact on blueberry, raspberry and cherry production in the Pacific Northwest. Find tips for detecting and monitoring spotted wing drosophila in this WSU Extension publication.

New Pests of the Understory,” a longer version of this blog post, originally appeared in the summer 2016 issue of Forest Stewardship Notes, a free e-newsletter published quarterly by Washington DNR and Washington State University Extension.

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