New Pests of the Understory

In a time of world trade and global movement of people and products, hitchhiking insects are becoming more and more common. In the past 20 years, almost 60 exotic insect species have established in Washington state. Some of these hitchhikers can become serious agricultural and forestry pests. The risk continues to grow as global markets continue to expand.

A 2010 study led by Julieann Aukema, a forest ecologist with the National Center for Ecological Analysis and Synthesis in Santa Barbara, California, estimated that there is 32 percent risk that a wood boring insect more damaging than the emerald ash borer will be introduced into the United States in the next ten years. In addition to exotic insects that can cause significant economic impacts to agriculture and natural resources, there are a number of species affecting the natural and cultural ecosystems. The following are a few examples of newly introduced insects that are, or likely will, impact the forest understory and those that rely on it.

Viburnum leaf beetle

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

The viburnum leaf beetle (VLB), Pyrrhalta viburni, was first discovered in Washington state in Whatcom County in 2004. Since then, it has spread down to King County. Recent collections of VLB have been made in Spokane. VLB overwinters in its egg state in the stems of last year’s new viburnum growth. Larvae hatch when the first leaves unfold in spring. Damage caused by feeding larvae is very distinctive and won’t be confused with any other feeding damage on viburnums. After feeding, larvae migrate to the soil to pupate for a few weeks. Adults emerge and continue to feed on foliage causing additional damage. Adult beetles feed, mate and lay eggs until first frost. Viburnum plants are not able to tolerate multiple defoliation events over consecutive years. The native Viburnum edule, high bush cranberry, is susceptible to attack. Many wildlife species rely on high bush cranberry for a reliable food source. To learn more about the viburnum leaf beetle in Washington state.

Lily leaf beetle

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

The lily leaf beetle (LLB), Lilioceris lilii, was discovered in Washington state just outside of Seattle in Bellevue during the spring of 2012. Thus far, LLB has only been found in Bellevue, Seattle and Issaquah. Adult beetles are very conspicuous as scarlet red beetles. Adults overwinter in protected areas and move to feed, mate and lay eggs on emerging true lilies (Lilium spp.) and fritillaries (Fritallaria spp.) in the spring. Eggs are laid in irregular rows on the underside of the lily leaves. Once eggs hatch, beetle larvae feed on the lily foliate and developing flower buds. Larvae cover themselves in excrement and other debris as a defensive tactic and superficially resemble slugs. Two key native species in the Pacific Northwest that are likely susceptible are the tiger lily, Lilium columbianum, and the chocolate lily, Fritillaria lanceolate. Learn more about the lily leaf beetle in Washington state.

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 Seattle, King County, in 2008. The following year, it was identified in Oregon. Lace bug nymphs emerge from eggs in the spring. Having a piercing-sucking mouthpart, the nymphs feed by removing the liquids from plant leaves creating a stippled or bronzed burn on the leaf surface. Distinctive tar spots appear on the undersides of leaves as evidence of their presence. Adult lace bugs are quite attractive with a clear, lacy appearance. In the Pacific Northwest there will be multiple generations per year. Azalea lace bugs are causing significant damage and mortality to landscaped azaleas and rhododendrons in both the Seattle and Portland areas. What is most concerning about this newly introduced insect is the degree of damage it can cause and the expanded host ranges documented in the Pacific Northwest. Jim LaBonte from Oregon Department of Agriculture has found damage on huckleberry and salal in addition to other native plant species. Learn more about the azalea lace bug in the Pacific Northwest.

Spotted winged drosophila

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

The spotted winged drosophila (SWD), Drosophila suzukii, is a significant new pest to many small fruits and has had a major impact on blueberry, raspberry and cherry production in regions of the Pacific Northwest. SWD was first discovered in 2009 in Seattle, just shortly after its detection in California the previous year. Since then, SWD has spread across the continent. SWD adults overwinter in protected areas. When berries and other food resources become available in spring, SWD adults lay eggs into ripening fruit using an ovipositor—an appendage—with a saw-like edge. The ability to egg-lay in under-ripe fruits has made this fruit fly a serious pest. Being a fruit fly, SWD has a high reproductive capacity and fast generation time. Populations can build rapidly. Larvae feed on the flesh of fruit and quickly cause the fruit to rot. Larvae pupate outside the fruit and emerge as adults to repeat the process.

In 2013, SWD was found infested huckleberries at high elevations in the Indian Heaven Wilderness Area of the Gifford Pinchot National Forest. Almost 50 percent of the huckleberries picked turned to be infested by SWD. Since 2013, SWD has consistently been collected from infested huckleberries in high elevations (5100 feet) in remote areas. SWD was able to disperse successfully in nooks and crannies of the Mount Adams and Mount Hood forests very rapidly. SWD has likely done so in other forests where huckleberries are common.

The economic impact to agriculture and natural resources of new pests is the focus for research and investments; there are few resources available to understand the impact on natural and cultural systems. The significance of these new pest introductions into natural areas has yet to be fully realized. To put it in perspective however, humans have harvested huckleberries from the Indian Heaven Wilderness Area for almost 10,000 years without experiencing wormy, rotten berries until now.

By Todd A. Murray, Director, WSU Agricultural and Natural Resources Extension Program Unit
tmurray@wsu.edu