Northwest Office

Northwest Regions

Invasives on the Horizon

Although the names of current invasives are well known, what are invasives that we should be aware of? We asked the experts what invasives worry them, and here’s what they shared.

Hokkaido Gypsy Moth

By Karen Ripley

Many species and subspecies of gypsy moth are visually
indistinguishable, so regulatory agencies use genetic tools to
identify the species, and enable inferences about behaviors to
devise effective response strategies. This moth is a female Asian
gypsy moth (Lymantria dispar asiatica).

Photo courtesy of John Ghent,

The triangular red, green or brown traps you see from June to September, fastened on roadside tree trunks across the United States, are usually gypsy moth detection traps. States outside the currently infested area, especially those with commercial ties to Asia, are continuously attentive to possible introductions of gypsy moth, Lymantria dispar and use pheromone-baited traps to locate new populations. There are several subspecies of L. dispar: a “European” variety that was introduced to Massachusetts in the 1860s and which feeds on an extensive number of broadleaved trees and plants, and has spread widely across the eastern United States and Canada; and “Asian” varieties that are regularly carried in on ships and equipment from China, Japan, South Korea, and Russia and which feeds on foliage of conifer trees in addition to dozens of other trees and plants and not currently established in North America.

The Asian varieties of gypsy moths (subspecies L. dispar asiatica and L. dispar japonica and closely related species L. albescens, L. mathura, L. monacha, L. postalba and L. umbrosa) are considered an extreme threat to the western US because these caterpillars feed on conifer foliage and female flight behavior makes them able to spread quickly and potentially elude control efforts. Fortunately, many of the Lymantria species respond to similar sex attractant pheromones, so every gypsy moth caught in annual detection trapping programs (implemented by state departments of agriculture or forestry) is submitted for genetic analysis to inform response actions.

In 2019, a gypsy moth captured north of Seattle, in Woodway, Snohomish County, Washington, was determined to be Lymantria umbrosa, informally known as the “Hokkaido” gypsy moth. It was the first record of this species being caught in North America. After environmental analysis, and under an emergency order of the Governor, the Washington State Department of Agriculture responded in May 2020 by spraying 672 acres across the moth capture site with three aerial applications of the microbial insecticide Bacillus thuringiensis kurstaki. The area will be monitored with a dense array of pheromone traps for at least three years to confirm whether the treatment was effective and that Hokkaido gypsy moth, for now, won’t be making North America its new home.

Contact: Karen Ripley

Annual Grasses—Ventenata and Medusahead

By Shawna Bautista

Most invasive plants are not thought to be direct threats to forest ecosystems, but recent research indicates that invasive annual grasses may be more of a threat than commonly recognized. Two species, Ventenata (Ventenata dubia) and Medusahead (Taeniatherum caput-medusae), are gaining attention in the western United States as significant threats to arid shrublands, as well as dry forest ecosystems. Both species are native to Mediterranean regions and are spreading rapidly, particularly in the northwest. Recent fires in Oregon have demonstrated that areas adjacent to and within dry forests that are invaded by ventenata can carry fire to and through forested areas. Rapid post-fire colonization may impede reforestation and lead to the same kind of grass-fire cycle we have seen with cheatgrass in the Great Basin. Thinning and juniper removal activities can also unintentionally spread invasion by these species, increasing fire spread, incidence and frequency. Resulting invasion and potential fire spread are counter-productive to the purpose of our projects, so close attention to preventing introduction, pre-project treatments, and post-project treatments is warranted.

Contact: Shawna L. Bautista,

Asian Giant Hornet aka: Murder Hornet

By Karen Ripley

Asian giant hornets are extremely large yellow-jacket-type
insects that are capable of decimating honeybee colonies
and hives. Photo courtesy of Washington State
Department of Agriculture

The Asian giant hornet (AGH) (Vespa mandarinia; known in popular culture as the “murder hornet”) is an extremely large yellow-jacket-type insect that was first observed in British Columbia and Washington in late 2019. This invasive species is a highly evolved predator of honeybees. It can decimate a colony/hive, killing workers and stealing the larvae and pupae within a few hours. Like other hornets, AGH also have potent venom in their sting, the ability to sting many times, and aggressive behavior when they feel threatened, especially when their ground nests or the beehives they are attacking are approached.

Based on reported sightings of large, conspicuous insects (AGH are 11⁄2 to 2 inches long with orange heads), specimens collected, and evidence of bee kills (destroyed hives; with hundreds of decapitated workers), the Washington State Department of Agriculture (WSDA) developed a 2020 response strategy intending to eradicate AGH. The focus area is northern Whatcom County. Since we don’t know how AGH reached North America, their warnings, fact sheets and strategies are being widely publicized.

WSDA’s tactics target the seasonal lifecycle and behaviors of AGH, which are like the familiar annual cycle of other yellow jackets.

In early spring new queens emerge from overwintering sites and are attracted to feed on tree sap. WSDA designed adhesive “sap traps” around deliberately wounded trees to catch queens. As young AGH workers begin to forage in early summer, seeking carbohydrate and protein, “bottle traps” baited with orange juice solutions and observations by alert beekeepers should provide clues to locate and destroy nearby colonies. In late summer, when groups of AGH workers seeking protein aggressively attack beehives, rapid reports from beekeepers will be even more critical to intercepting workers in order to locate and destroy all AGH colonies before the next generation of queens emerges in the fall.

Interacting with AGH is dangerous. Approaching and eradicating active colonies requires trained employees equipped with protective gear and pesticides.

The WSDA website is the best source of immediate, up-to-date AGH information.

Contact: Karen Ripley karen.ripley@


Exotic Wood-boring Insects

By Jim LaBonte

Asian Longhorned beetle
Photo courtesy of Lim LaBonte

Introduction of exotic wood-boring insects is a global phenomenon. Many such species have become established in the Pacific Northwest and new exotic wood-borers are found here every year. Several have already caused major damage in the region, such as walnut twig beetle, Pityophthorus juglandis. There are many other damaging exotic wood-borers not yet known from the Pacific Northwest, such as Asian longhorned beetle, Anoplophora glabripennis, and emerald ash borer, Agrilus planipennis. These pests threaten native and urban forests, ornamental and indigenous shrubs, orchards, and timber production.

The cause of this problem is no mystery—it is the global economy. While exotic wood-borers infest imported commodities, such as wood in the form of art objects and lumber, and woody nursery stock, probably the greatest source of these pests is solid-wood-packing material. Once in North America, exotic wood-borers are further spread by domestic products, such as firewood and nursery plants.

Although many exotic wood-borers, such as emerald ash borer and walnut twig beetle, attack only a few hosts, some species, such as the Asian longhorned beetle, attack many broad-leaved trees. Still other species, like some ambrosia beetles, can attack hundreds of both broad-leaved and coniferous hosts. While stressed hosts suffering from drought and disease are often most vulnerable to insect attacks, pests like Asian longhorned beetle, emerald ash borer, and walnut twig beetle can attack healthy trees.

Effective response to these pests is challenging. The best approach is to prevent introduction through strong international regulations, but enforcement resources are too few and importers often flout regulations. Early detection, the second-best tactic, is hampered by this country’s limited insect identification resources and detection technologies are inadequate. Funding for the constant surveys needed is not sufficient. Eradication and control are very difficult because of poor detection technologies and few effective pesticides. Unless there are dramatic improvements in regulations and enforcement, detection, and eradication and control options, exotic wood-boring insects will continue to enter the Pacific Northwest and pose major risks to our environment and economy.

Contact: Jim LaBonte jlabonte@


Spotted Lantern Fly

By Karen ripley

Spotted lantern fly is a significant pest in a number of East
Coast states, and its preferred host tree is Tree of Heaven,
a widely planted street and ornamental tree original from China.
Photo courtesy of Richard Gardner,

The spotted lantern fly (SLF) (Lycorma delicatula) is a large plant-hopper insect that is native to eastern Asia (China, India, and Vietnam). Most life stages have conspicuous white, black, and red coloration and piercing mouthparts used for sucking juice and sap from fruit and plant tissues. Adults are about one inch long and have conspicuous red hindwings.

SLF were first observed in the eastern United States in 2014 and have become significant pests in Pennsylvania, New Jersey, Delaware, Virginia, and Maryland. High numbers of SLF are a repulsive annoyance to homeowners. Feeding wounds reduce the quality and shelf life of fruit and threaten associated industries with quarantines intended to prevent additional spread. Crops that are favored by SLF include apples, grapes, hops, and cherries. In forests, SLF can be found on maple and birch trees. SLF lay eggs on hard surfaces like rocks, trees, outdoor equipment and houses.

The most highly favored aggregation and egg laying site for SLF is the “Tree of Heaven” (ToH) Ailanthus altissima, a large deciduous tree originally from China that has been widely planted as an ornamental and street tree throughout the United States. ToH is also invasive and can be spread short distances by underground root suckers, medium distances by winged seeds (like maple samaras), and long distances when people move and cultivate it.

SLF is not known to be present on the West Coast. It could easily be transported here if adults or eggs hitchhike on infested crops, equipment, firewood, or objects from the East Coast or Asia. In addition to inspecting crops and goods that could harbor SLF, monitoring ToH will be a key part of early detection. Efforts are getting started to inventory ToH, encourage removal of ToH, and maintain/monitor a few individual male ToH in high risk areas. Such trees could serve as sentinels by being inspected regularly to facilitate promptly detecting SLF when/if it arrives.

If you see a SLF, capture and report it through an Invasive Species Reporting site such as Improve your awareness of ToH identification (https://extension. and local occurrences; look for SLF nearby.  u

Contact: Karen Ripley

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