Oregon’s forests, gardens, and agricultural lands face mounting threats from invasive insects that arrived from distant continents. These non-native pests reproduce rapidly, often without natural predators to keep their populations in check. You play a crucial role in protecting your community by learning to identify these destructive species and reporting sightings early, before populations become impossible to control.
The emerald ash borer has already spread to five Oregon counties, triggering permanent quarantines in the Portland metro area. Brown marmorated stink bugs damage agricultural crops worth millions annually. Spotted wing drosophila destroys berry harvests across the state.
Early detection by vigilant residents like you remains the most effective defense against these invaders. By the time an outbreak becomes obvious, control efforts often prove too expensive and challenging to succeed.
1. Emerald ash borer
The emerald ash borer (Agrilus planipennis) represents one of Oregon’s most urgent invasive threats, with established populations now confirmed in Multnomah, Washington, Clackamas, Yamhill, and Marion counties. This metallic green beetle measures just one-third to one-half inch long but causes devastating damage to ash trees throughout its range.
Adult beetles display a brilliant metallic green color with a coppery red or purple abdomen visible when their wings spread. They emerge from trees in late May through July, leaving distinctive D-shaped exit holes approximately one-eighth inch in diameter in the bark. The larvae, which are creamy white with bell-shaped body segments, tunnel beneath the bark and feed on the tree’s vascular tissue, cutting off nutrient and water flow.
Key Insight: Oregon ash (Fraxinus latifolia) is an ecologically important riparian species native to the state. The emerald ash borer threatens these trees along streams and rivers, where they provide critical habitat for fish and wildlife.
You can identify infested trees by looking for canopy dieback starting at the top, increased woodpecker activity creating large patches of missing bark, and epicormic sprouting where new shoots emerge from the trunk. The Oregon Department of Agriculture maintains a permanent quarantine prohibiting the movement of ash or fringe tree wood from affected counties. Never transport firewood more than 10 miles from where it was cut, as this remains the primary way people accidentally spread the beetle to new areas.
If you spot signs of emerald ash borer damage, report it immediately to the Oregon Invasive Species Hotline at 1-866-INVADER (1-866-468-2337). Native wood-boring beetles like the golden buprestid look similar but are larger with copper-colored edges, so proper identification matters.
2. Brown marmorated stink bug
The brown marmorated stink bug (Halyomorpha halys) has become a familiar nuisance pest in Oregon homes and a serious threat to agricultural production. This shield-shaped insect measures about five-eighths inch long and displays mottled brown coloring with distinctive white bands on its antennae and alternating light and dark bands along the edges of its abdomen.
These invasive pests aggregate on the sunny sides of buildings during fall, seeking protected spaces to overwinter. You’ll find hundreds clustering on home exteriors, often working their way indoors through tiny cracks and gaps. Their populations vary dramatically from year to year depending on climatic factors, with some seasons bringing massive invasions that overwhelm homeowners.
The agricultural damage extends far beyond the household nuisance. Brown marmorated stink bugs feed on more than 100 plant species, using their piercing-sucking mouthparts to extract plant juices from fruits, vegetables, and ornamental plants. They cause particular damage to apples, pears, cherries, peaches, tomatoes, peppers, and soybeans. Their feeding creates dimpled, scarred areas on fruits that make them unmarketable, resulting in significant economic losses for Oregon growers.
Pro Tip: Never crush brown marmorated stink bugs indoors. They release a pungent odor when threatened or crushed. Instead, vacuum them up or sweep them into a container of soapy water.
Oregon State University Extension researchers continue developing integrated pest management strategies for this invasive species. The USDA has approved the release of Ganaspis brasiliensis, a parasitic wasp that attacks the bugs in their native Asian range, as a biological control agent. You can help scientists track population patterns by reporting sightings through the OSU Extension stink bug collection.
3. Asian longhorned beetle
The Asian longhorned beetle (Anoplophora glabripennis) poses a catastrophic threat to hardwood trees in North America, though it hasn’t been detected in the Pacific Northwest yet. This large, distinctive insect measures 0.75 to 1.5 inches long with a shiny jet-black body marked by bright white spots. Its extremely long antennae, banded in black and white, extend 1.5 to 2.5 times the beetle’s body length.
Important Note: While not currently established in Oregon, suitable habitat exists throughout the state. Remaining vigilant for this pest helps prevent establishment before populations explode.
Adult beetles chew round depressions in tree bark where females lay eggs. The larvae bore deep into the wood, creating tunnels throughout the tree’s heartwood that weaken structural integrity and eventually kill the tree. Unlike many wood-boring insects that only attack stressed or dying trees, Asian longhorned beetles readily infest healthy, vigorous trees.
| Characteristic | Asian Longhorned Beetle | Native Beetles |
|---|---|---|
| Size | 0.75-1.5 inches | Usually smaller (under 0.5 inches) |
| Antennae | 1.5-2.5x body length, banded | Shorter, often solid colored |
| Exit Holes | Perfectly round, 0.375 inches diameter | Oval or D-shaped, smaller |
| Host Trees | Maples, willows, elms, birches | Usually specific to one tree genus |
| Tree Health | Attacks healthy trees | Primarily stressed trees |
This beetle threatens maple, willow, elm, birch, ash, and poplar trees. A single infestation in an urban area could require removing thousands of trees within a half-mile radius to prevent spread. Detected infestations in other states have cost hundreds of millions of dollars in eradication efforts.
Watch for perfectly round exit holes about three-eighths inch in diameter, coarse sawdust (frass) at the tree base or in branch crotches, and oozing sap on the trunk or branches. Report any suspected Asian longhorned beetle sightings immediately to state agricultural officials, as early detection remains the only hope for successful eradication.
4. European paper wasp
The European paper wasp (Polistes dominula) has become Oregon’s most common paper wasp species since its arrival in the 1970s, effectively displacing native Polistes species through competitive advantages. This slender wasp measures about three-quarters of an inch long with distinctive yellow and black markings. Unlike native paper wasps, European paper wasps display bright yellow antennae and legs with minimal black coloring.
You can distinguish European paper wasps from native species by examining their markings closely. They have black anchor-shaped or thick reverse teardrop markings behind the head, whereas native paper wasps typically show more extensive black coloring. Their yellow faces lack the dark markings common on native species.
These invasive wasps build exposed, umbrella-shaped paper nests under eaves, porch ceilings, deck railings, and similar protected locations around structures. Colonies grow throughout summer, with some reaching several dozen workers by late season. They exhibit more aggressive nesting behavior near human structures compared to native species, increasing the likelihood of defensive stinging incidents.
Common Mistake: Many people assume all paper wasps are native beneficial insects. European paper wasps are invasive and more likely to nest in high-traffic areas around your home than native species.
European paper wasps do provide some beneficial pest control by hunting caterpillars, fly larvae, and other small insects to feed their larvae. However, their competitive dominance over native pollinators and tendency to build nests in inconvenient locations make them a net negative for Oregon ecosystems. They’re particularly problematic at outdoor events and recreational areas where their defensive behavior poses stinging risks.
Managing European paper wasp nests requires caution. Nests located away from high-traffic areas can often be left alone, as the colony dies off naturally in fall. For nests in problematic locations, removal should occur during early morning or evening when wasps are less active. Consider consulting pest management professionals for large or difficult-to-reach nests.
5. Box tree moth
The box tree moth (Cydalima perspectalis) threatens boxwood plants throughout Oregon, though establishment remains limited compared to its devastating impacts in Europe. This distinctive moth displays white wings with a purple-brown border, though some individuals show almost entirely brown wings. Adults have a wingspan of about 1.5 inches and hold their wings in a distinctive triangular shape when at rest.
The larvae cause the primary damage to boxwood plants. Young caterpillars are yellowish-green with black heads, while mature larvae develop distinctive black and white stripes along their bodies and grow up to one inch long. They feed voraciously on boxwood foliage, starting inside the plant where damage remains hidden initially. Heavy infestations can completely defoliate boxwood shrubs, leaving only bare stems and webbing.
You’ll notice several warning signs of box tree moth infestation:
- Webbing visible in the plant interior
- Green or brown frass (caterpillar droppings) on leaves and branches
- Yellowing or browning foliage starting from the plant’s center
- Stripped leaves with only the midrib remaining
- Caterpillars visible on foliage during inspection
The moth produces multiple generations per year in suitable climates, allowing populations to build rapidly when established. Adult moths fly during summer months, and females lay egg masses on the undersides of boxwood leaves. The species overwinters as larvae hidden within webbing in the plant interior, making winter a good time to inspect boxwoods carefully.
Pro Tip: Inspect new boxwood plants thoroughly before purchasing or planting. Box tree moth commonly spreads through the plant trade when infested nursery stock moves to new areas.
European gardens have struggled to control box tree moth since its arrival from Asia. Some historic boxwood gardens lost centuries-old specimens to this pest. Oregon’s cooler climate may limit the moth’s reproductive success compared to warmer regions, but vigilance remains essential. Report any suspected box tree moth sightings to help prevent establishment in new areas of the state.
6. Spotted wing drosophila
The spotted wing drosophila (Drosophila suzukii) has become Oregon’s most economically damaging invasive fruit pest since its detection in 2009, causing millions of dollars in losses to berry and cherry growers annually. This tiny fruit fly measures just one-eighth inch long but possesses a unique ability among drosophila species: females have a serrated ovipositor that allows them to lay eggs in healthy, ripening fruit rather than only damaged or rotting fruit.
Male spotted wing drosophila display a distinctive dark spot on the leading edge of each wing, making identification straightforward. Females lack this spot but show the characteristic serrated egg-laying organ visible under magnification. Both sexes have bright red eyes and tan-colored bodies with dark bands across the abdomen.
| Fruit Type | Damage Pattern | Economic Impact | Critical Period |
|---|---|---|---|
| Cherries | Soft, sunken areas near stem | High – entire crop can be lost | Late June-July harvest |
| Strawberries | Larvae inside fruit, collapsed areas | Moderate to high | May-September |
| Blueberries | Soft, leaky berries with larvae | Very high – major crop in Oregon | July-September harvest |
| Raspberries | Larvae in fruit, premature softening | High | June-October |
| Blackberries | Internal larvae, seeping juice | High | July-September |
The fly’s rapid reproduction rate compounds the damage. Spotted wing drosophila can complete a generation in as little as two weeks during warm weather, with females laying up to 350 eggs during their lifetime. They target strawberries, raspberries, blackberries, blueberries, cherries, and other thin-skinned fruits. Larvae develop inside the ripening fruit, making the damage invisible until harvest.
Commercial growers face difficult management decisions. Integrated pest management strategies include intensive monitoring with traps, timed insecticide applications, prompt harvest of ripe fruit, and sanitation to remove overripe or damaged fruit that serves as breeding sites. Home gardeners should harvest berries frequently, refrigerate fruit immediately, and destroy infested fruit to reduce population buildup.
Oregon State University researchers have contributed significantly to understanding spotted wing drosophila biology and management. The USDA approved release of a parasitic wasp (Ganaspis brasiliensis) that attacks the fly’s larvae, offering hope for biological control that reduces reliance on insecticides.
7. Light brown apple moth
The light brown apple moth (Epiphyas postvittana) arrived in California in 2007 and poses a potential threat to Oregon agriculture, though established populations remain limited in the Pacific Northwest. This small moth displays light brown coloring with darker brown markings on the forewings, though individual appearance varies considerably. Adults measure about one-half inch long with a wingspan of three-quarters inch.
This invasive pest earned its name from attacking apple orchards, but it actually feeds on more than 500 plant species including ornamentals, fruit trees, vegetables, and native plants. The moth’s extreme polyphagy makes it a severe threat to diverse agricultural systems and natural ecosystems. Larvae web leaves together and feed within the protected space, causing irregular holes and damaged growing tips.
You can identify light brown apple moth damage by looking for leaves webbed or rolled together with silk, often at branch tips. The larvae are cream-colored to light green with a brown head capsule and grow to about three-quarters inch long. They’re active year-round in mild climates, with overlapping generations that make population monitoring challenging.
Important Note: Light brown apple moth closely resembles several native tortricid moths. Professional identification is essential before implementing control measures to avoid harming beneficial native species.
The moth’s establishment in Oregon could force significant changes to pest management programs across multiple agricultural sectors. Quarantines and increased monitoring requirements might disrupt plant trade, while control costs would burden growers already managing numerous pest pressures. Wine grape production faces particular vulnerability, as the larvae damage grape clusters and create entry points for disease-causing fungi.
California’s attempted eradication program, which included controversial aerial pesticide applications over urban areas, ultimately failed to eliminate the moth. This experience suggests that preventing establishment through early detection offers the best management strategy. Report unusual moth or caterpillar activity on multiple plant species to help track potential light brown apple moth expansion.
8. Gypsy moth / spongy moth
The gypsy moth (Lymantria dispar), recently renamed spongy moth to avoid using an ethnic slur, ranks among North America’s most destructive forest pests but hasn’t established breeding populations in Oregon yet. This large moth displays dramatic sexual dimorphism: males have brown wings with wavy black bands and fly readily, while larger females have white to cream-colored wings with similar black patterns and cannot fly despite their wingspan of up to 2.5 inches.
Key Insight: The moth’s recent name change to “spongy moth” references the spongy texture of the egg masses, which remain the species’ most distinctive and identifiable feature. This name also removes a term that had become a slur against Romani people.
Spongy moth caterpillars cause the primary damage through voracious defoliation of trees and shrubs. The larvae display distinctive markings: five pairs of blue dots followed by six pairs of red dots along their backs, with long hairs covering their bodies. Mature larvae reach up to 2.5 inches long. They feed primarily on oaks but consume more than 300 plant species when populations peak, occasionally defoliating entire forests.
The species spreads primarily through human activities. Egg masses attached to vehicles, firewood, outdoor equipment, and nursery stock move the moth to new areas. Each tan or buff-colored egg mass contains 100 to 1,000 eggs covered with a spongy texture of fine hairs from the female’s abdomen. These masses appear on tree trunks, buildings, firewood piles, outdoor furniture, and vehicles from July through the following spring.
Oregon’s strategic location between established West Coast populations and the massive Eastern infestation makes prevention crucial. Residents moving from areas with established spongy moth populations should carefully inspect their belongings for egg masses before relocating. The Oregon Department of Agriculture offers free inspections of outdoor household goods and recreational vehicles for people moving from northeastern states where the moth is common.
Watch for heavy defoliation of oak trees during late spring and early summer, distinctive egg masses on outdoor surfaces, large hairy caterpillars with blue and red dots on their backs, and light brown moths around outdoor lights in summer. Report any suspected spongy moth findings immediately, as successful eradication requires rapid response while populations remain small. Visit the Oregon Department of Agriculture website for inspection requests and reporting procedures.
9. Cabbage seedpod weevil
The cabbage seedpod weevil (Ceutorhynchus obstrictus) threatens Oregon’s valuable canola and mustard seed production, attacking plants in the Brassicaceae family. This tiny gray-brown weevil measures just one-eighth to one-quarter inch long with a distinctive long snout (rostrum) typical of weevil species. Its body shows mottled gray coloring with fine hairs giving a dusty appearance.
Adult weevils emerge in early spring and feed on cruciferous crops, but the larvae cause more severe economic damage. Females use their long snout to drill holes in developing seedpods, laying eggs inside. The white, legless larvae develop within the pods, feeding on developing seeds. A single larva can destroy up to 10 seeds in one pod, and heavy infestations significantly reduce seed yield and oil content in harvested crops.
Canola growers face particular challenges from this pest:
- Yield losses of 15-30% occur in heavily infested fields
- Pod damage allows entry of diseases that further reduce quality
- Small weevil size makes detection difficult during critical treatment timing
- Multiple generations in some areas compound damage
- Limited effective control options exist
You’ll spot signs of cabbage seedpod weevil infestation by examining developing seedpods for small entry holes about one-thirty-second inch in diameter. Splitting open pods may reveal white larvae or their frass inside. Adult weevils are most active during warm, sunny days in spring when they can be seen on flowering shoots. They drop from plants when disturbed, making sweep net sampling the most effective monitoring method.
Common Mistake: Many growers confuse cabbage seedpod weevil with flea beetles or other small insects on cruciferous crops. The weevil’s characteristic long snout distinguishes it from other pests.
Management strategies focus on monitoring adult populations and timing insecticide applications to prevent egg-laying. Oregon State University Extension provides regional recommendations based on growing degree day models that predict peak adult activity. Crop rotation, destruction of volunteer canola plants, and field sanitation help reduce overwintering populations.
10. Vine weevil
The vine weevil (Otiorhynchus sulcatus) causes serious damage to nursery plants, ornamentals, and berries throughout Oregon’s horticultural industry. Adult weevils are dull black beetles about three-eighths inch long with a short snout, fused wing covers preventing flight, and small patches of yellow scales or hairs on their bodies giving a slightly mottled appearance.
This pest inflicts damage at both life stages through different feeding patterns. Adult weevils create characteristic notching along leaf margins, producing a scalloped appearance that’s distinctive though rarely severe enough to kill plants. The real threat comes from the larvae, which are white, C-shaped grubs with brown heads that feed on plant roots below the soil surface. Root feeding weakens plants, stunts growth, and can kill valuable nursery stock or mature landscape plants.
All vine weevils are female, reproducing through parthenogenesis without males. This reproductive strategy allows rapid population expansion when the weevil establishes in new areas. Each female lays 500-1,000 eggs during her lifetime, depositing them on the soil surface or in growing medium near host plants. The eggs hatch in about two weeks, and the larvae immediately begin feeding on roots.
Pro Tip: Vine weevil adults cannot fly, so they must crawl between plants. Physical barriers, sticky bands around pot bases, and strategic spacing can help prevent spread in nursery or greenhouse settings.
Host plants include rhododendrons, azaleas, yews, hemlocks, strawberries, cranberries, grapes, and over 100 other ornamental and crop species. Container-grown nursery plants face particularly high risk since the confined growing medium concentrates larval damage on limited root systems. Infested container plants often show symptoms of drought stress despite adequate watering because damaged roots cannot absorb sufficient moisture.
| Life Stage | Damage Type | Timing | Visibility | Severity |
|---|---|---|---|---|
| Adults | Leaf notching | Spring-Fall | Highly visible | Low to moderate |
| Larvae | Root feeding | Year-round (peak Fall-Spring) | Hidden underground | High to severe |
| Pupae | None | Summer in soil | Not visible | No damage |
Detection requires vigilance since adult weevils are nocturnal and hide during daylight hours. Check for adults at night with a flashlight, or place burlap around plant bases to create daytime hiding spots you can inspect. Knocking plants over white paper or cloth can dislodge hiding adults. Root inspection remains the only reliable way to detect larval infestations before severe damage occurs.
Management options include biological control with beneficial nematodes (Steinernema and Heterorhabditis species) that parasitize larvae in the soil, barrier methods to prevent adult movement, and targeted insecticides. The Pacific Northwest Insect Management Handbook provides detailed control recommendations for commercial growers and nurseries dealing with vine weevil infestations.
Frequently Asked Questions
Contact the Oregon Invasive Species Hotline at 1-866-INVADER (1-866-468-2337) or submit a report through their online form. Include clear photos, exact location information, and a description of what you observed. The hotline connects you directly with experts who can provide identification assistance and coordinate rapid response if needed.
Firewood serves as the primary pathway for spreading invasive forest insects like emerald ash borer and Asian longhorned beetle. Insects hide in bark crevices and bore inside wood, remaining undetectable during transport. Oregon Department of Agriculture recommends keeping firewood within 10 miles of where it was cut. Always “buy it where you burn it” to protect forests statewide.
Invasive insects are non-native species that arrive from other continents or regions and cause ecological or economic harm in their new environment. They often lack natural predators, parasites, and diseases that controlled their populations in native ranges. Native insects evolved alongside local plants and animals, filling ecological roles without causing widespread damage. Some native insects can become pests under certain conditions, but they don’t spread uncontrollably like invasive species.
Management strategies vary significantly between species. Some invasive insects like European paper wasps and brown marmorated stink bugs can be managed with homeowner-level interventions. Others like emerald ash borer and spotted wing drosophila require professional assessment and potentially professional treatment. Always identify the pest correctly before attempting control, consult OSU Extension resources for current recommendations, and report detections to support tracking efforts.
While most invasive insects on monitoring lists cause significant damage, some introduced species become naturalized without major negative impacts. However, the 10 species covered in this guide all threaten Oregon’s forests, agricultural production, or native ecosystems. These species warrant attention, reporting, and management efforts to minimize their spread and impact.
Conclusion
Your awareness and prompt reporting create the foundation for Oregon’s invasive species defense. Early detection by observant residents allows agricultural officials and natural resource managers to respond before populations explode beyond control. The emerald ash borer spread demonstrates how quickly an invasive insect can expand once established, moving from a single county to five counties and triggering widespread quarantines.
Learn to recognize these 10 invasive insects and their distinctive signs. Check trees and plants regularly for unusual damage patterns, unfamiliar insects, or suspicious exit holes. Photograph anything concerning and report through proper channels rather than dismissing observations as probably harmless. Scientists and pest management professionals depend on citizen reports to track invasive species distribution across Oregon’s vast landscape.
Prevent unintentional spread by following firewood movement restrictions, inspecting plants before purchasing from nurseries, and cleaning outdoor equipment when moving between regions. Support local eradication and monitoring programs by allowing survey staff to place traps on your property when requested. Your cooperation protects Oregon’s forests, agricultural economy, and native ecosystems from these destructive invaders threatening everything from backyard gardens to commercial orchards.
