Emerging Pests in Pacific Northwest Ornamentals

Michael R. Bush, Sharon Collman and Sven Spichiger
Latest revision: 
March 2020

Introduced or exotic species are those species (including insects) that have been moved from their native range to a new habitat. Some introduced insects slip quietly into new habitats or geographic areas without drawing attention, and apparently cause no significant harm. Those that do cause damage to plants, structures, or human or environmental health are recognized as “emerging pests” and discussed in this section.

While the damage caused by these introduced pests has obvious impacts, costs associated with exotic species may be much broader. The economic impact of introduced pests may include any of the following: cost of monitoring the pest; loss of overseas markets; cost and management of quarantines; new rules and regulations; increased use of pesticides and their non-target impacts; containment or eradication costs; property damage and lost property taxes. Each of these impacts can have further ramifications to taxpayers, our communities and our environment. Science News (2011) reported that “non-native, wood-boring insects such as the emerald ash borer and the Asian long horned beetle exact an estimated $1.7 billion in local government expenditures, and approximately $830 million in lost residential property values each year.”

In the Pacific Northwest, most of our worst pests have been introduced from other areas of the world, or in some cases, other areas of the United States. Examples include black vine weevil, European crane fly, apple maggot, and San Jose scale. The Washington State Department of Agriculture maintains a list of introduced pests at:

https://agr.wa.gov/departments/insects-pests-and-weeds .

This section includes information on several new pests to the Pacific Northwest. World trade has increased the number of new invasive species in our gardens, crops and environment. If you find unusual insects, or pests that seem to be new or causing excessive damage, please contact Washington State Department of Agriculture (WSDA), the Washington Invasive Species Council or your local Extension office. For a more immediate response, capture a series of digital images and send the best photos to PestProgram@agr.wa.gov for identification.

For further information:

Rosetta, R. L. 2017. An Update on New and Emerging Pests in the Pacific Northwest. https://www.publicgardens.org/resources/update-new-and-emerging-pests-pa...

Washington Invasive Species Council. 2019. Priority Species. https://invasivespecies.wa.gov/priorities.shtml

Reoccurring Exotic Pest Species

Gypsy moth

Lymantria dispar

The European gypsy moth was first detected in Washington in 1974. Another strain of gypsy moth, the Asian gypsy moth, has been intercepted 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 continue and have been successful in preventing permanent populations of gypsy moth in the PNW.

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 most hardwood trees, conifer trees and over 500 shrubs and plants in the Pacific Northwest. In parts of northeastern US, this species can defoliate entire forests. Homeowners should be on the search 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 often laid on the bark of the host trees, but may be laid on shipping containers, automobiles, RVs, firewood, door frames, window sills, 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 moth, 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 with you to eradicate this pest as soon as possible. WSDA uses an IPM approach that may employ the use of biological, mechanical, cultural, or 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

Japanese beetle

Popillia japonica

The Departments of Agriculture in Oregon and Washington State have been trapping for adult Japanese beetles for over 30 years. Isolated infestations of this beetle have been successfully eradicated in the past. In 2016, hundreds of adults were trapped near Portland, triggering another eradication effort. Quarantine areas are in place and this eradication program is expected to continue until at least 2021.

Pest description and damage The adult beetle is a colorful flower beetle with iridescent copper-colored wings and a metallic green thorax with a series of tufts of white hair along the perimeter of the abdomen. The adult measures about 0.375 of an inch long. In the summer months, these adults congregate and skeletonize the leaves on a wide range of ornamental plants including roses, phlox, mallow, asters, maples, oaks, willows, lindens and rhododendrons, as well as crops including peaches, cane berries, grapes, hops, potatoes and tomatoes. In late summer these adults mate and lay eggs in the soil beneath host plants. The mature larvae are C-shaped white grubs that tunnel under the ground surface, feed on the roots of grasses and are most likely to be found in lawns during the spring. Japanese beetle larvae are considered serious turf pests in eastern North America. The Japanese beetle overwinters as larvae in the soil and pupates in soil chambers in the spring. There is one generation each season. Nevertheless, this insect is capable of building up a large population in a short period of time.

Pest monitoring Traps that rely on an aggregation pheromone to attract and monitor both male and female beetles are commercially available. WSDA traps for Japanese beetle every year. Most Japanese beetle detections are associated with air cargo.

Management This is a quarantined pest species. If you suspect you have found plant damage, turf damage, the C-shaped larvae or the adult beetle, do not hesitate to report the finding to the State Department of Agriculture or local university Extension office. When confirmed as a Japanese beetle, these state agencies will respond and work with you to eradicate this pest as soon as possible. Several pesticide products, both organic and conventional, that target the adult and the larval stages of the Japanese beetle are available.

For further information:

Suits, R., H. Stoven, G. Langellotto-Rhodaback & C. Burfitt. 2017. Japanese Beetles in Oregon. https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pd... Washington

New In 2019

Asian giant hornet

Vespa mandarinia

Invasive hornets, including the Asian giant hornet, have been intercepted and eradicated in ports throughout the Pacific Northwest. In 2019, this species was confirmed in British Columbia and believed to be eradicated. In December, this hornet was found near the border of Washington State and British Columbia. WSDA will actively pursue and eradicate any reports of the Asian giant hornet.

Description and damage This hornet resembles our native yellowjacket wasps, but adults can be nearly 2 inches long. Adults have a distinctly yellow-orange head with prominent black eyes, black thorax and black/yellow striped abdomen. This hornet preys on large insects and will invade honey bee nests to decapitate workers and feed on the colony brood and provisions. These hornets will sting humans and animals but only when their underground nests are disturbed. As with any yellowjacket, hornet or bee sting, seek medical attention immediately if stung multiple times, or if you experience symptoms of an allergic reaction.

Biology and life cycle This hornet nests and forms colonies in underground chambers early in the spring. During the summer the nest expands in size and number. Between July to October homeowners are most likely to encounter foraging adults.

Pest monitoring If you suspect you have found a honeybee colony damaged by this species, or suspect you have encountered this large hornet, please report the finding to the State Department of Agriculture or local university Extension office. When confirmed as an invasive hornet of concern, these state agencies will respond and work with you to eradicate this pest as soon as possible.

For further information:

McGann, C. 2019. Pest Alert: Asian giant hornet. WA State Department of Agriculture Ag Briefs. https://wastatedeptag.blogspot.com/2019/12/pest-alert-asian-giant-hornet...

Previously listed emerging pests

(Dates in parentheses are the years pests were first found in the Pacific Northwest.)

Cabbage whitefly (2016)

Aleyrodes proletella

While cabbage whitefly is primarily a new pest of brassica crops. It also attacks other brassicas that are bedding plants and ornamentals.

Pest description and damage Cabbage whitefly is most likely to infest outer or exposed leaves of brassicas. Damage is often limited to curling, yellowing and the presence of sooty mold growing on the honeydew. Many plants are reported to be tolerant of infestations by this pest. Cabbage whitefly damage is limited to outer leaves and to ornamental brassicas, especially ornamental leafy kale. When the problem is persistent, check related weeds for whiteflies which can then fly to more valuable plants. Adults are small, white, moth-like, have white wings and a waxy, white thorax. When abundant, they fly up in great clouds from host plants. The nymphs are whitish-green, flattened and oval with dense waxy exudate covering them. The different species of whitefly look very similar, but by comparing photos they can be differentiated. Cabbage whitefly might be mistaken for the greenhouse whitefly, but GHW have long wings and a yellow thorax and a much wider host range. Adults and nymphs are vectors of a great number of viruses.

Biology and life cycle Adults overwinter on the host plants, including nearby related weeds. Cabbage whitefly spend the entire year on the host plants.

Pest monitoring The presence of paper wasps and yellowjackets cruising through ornamental beds should cause the gardener to check plants more closely. These wasps are great predators and if they are abundant it is likely that they are finding some prey. Monitor for whitefly with yellow sticky traps next to suspect plants.

Management—cultural control

Isolate all incoming plants in a separate area until you can inspect them for the presence of eggs, nymphs or pupae. The more visible adults may not be present at the time your shipment arrives.

Management—biological control

There are several effective biological control organisms such as the parasitic wasp, Encarsia formosa and the predatory beetle Delphastis. A good biocontrol consultant can match host whitefly to an effective predator or parasitoid and can guide you on timing releases.

For biology, life history, monitoring and management

See “Whitefly” in:


See “Whitefly” in Table 1:

For further information:

Oregon Department of Agriculture. 2016. Pest Alert: Cabbage Whitefly, Aleyrodes proletella. https://www.oregon.gov/ODA/shared/Documents/Publications/IPPM/CabbageWhi...

Southern green stink bug (2015)

Nezara viridula

The southern green stink bug was first reported south of Seattle near Seattle University and Seward Park. They were damaging cherries and raspberries and were already abundant, suggesting that they may have been in the area for several years before being reported in 2015.



Pest description and damage Southern green stink bug adults are green, usually with three light dots along the front edge of the triangular pronotum. There are several color variations of this species and sometimes the overwintering adult will change to brown, then back to green in spring. This can confound the identification process. So far, most of the stink bugs submitted in Washington have been the standard light green color. Usually among the adult SGSB will be distinctive young nymphs with black and white or green and white spots. (The spotted pattern is easy to see though it changes with each of the 5 molts). SGSB can be confused with green stink bug (GSB) with similar light green adults, but GSB nymphs do not have the distinctive spots. Eggs are laid in patches of about 20-30 eggs each; with a total of 30 to 130 each year per female. If you are not sure of the ID, samples can be photographed and submitted to the mapping website [see insert] or taken to county Master Gardener clinics or to local Extension offices. Damage depends on the plant part attacked and can include wilting buds, tar spots on fruit or leaves, honeydew or sooty mold, fruit with cat-facing, sunken areas, or dark corky areas within. These stink bugs can become a nuisance when they overwinter in homes, but they do not reproduce in households nor do they bite people. All stages emit a repugnant odor, which smells a bit like bleach.

Biology and life cycle The southern green stink bug adults overwinter under bark, in leaf litter, or more notably in house walls, attics and other protected areas. As soon as the spring weather warms, they emerge and start laying eggs. Eggs hatch in 5 days to 3 weeks depending on temperature. The first nymphs look like small dark dots and cluster on the eggs for protection. They do not feed until they molt to the second instar a few days later. There are a total of five instars, each taking about 5-7 days to develop. Each instar is strikingly colored with black and white spots. The fifth and final instar will have visible wing buds, a warning that the next stage will be green egg-laying adults. In warmer climates, there may be up to four generations a year.

Pest monitoring Several traps are available on the market for commercial growers and homeowners. For small scale trapping, an aluminum turkey pan with a half-gallon of water and a bit of detergent soap placed under an incandescent light at night has proven effective. A variety of pheromone traps can be used to monitor this stink bug species. Sweeping with a net may be useful in shrubbery and low hanging tree branches. Beating vegetation (including perimeter weeds), bushes, branches over a large tray or pizza box will dislodge both adults and nymphs. As fall arrives check the south and west side of the home for aggregating adults. They will work their way inside as it gets colder. In Washington, all the specimens taken are valuable to our stink bug survey.

Management—cultural control

During late autumn, remove landscape weeds and plant debris where stink bugs will overwinter. Trap crops, such as beans, can attract stink bugs. Consider planting perimeter rows of a trap crop in early spring. When stink bugs are found later in the spring, destroy or spray the trap crop. Use floating row cover, well-sealed, to prevent stink bugs from settling on your shorter crops.

Management—physical control

Remove home-invading stink bugs by hand or with a shop vac. In late autumn or early spring, vacuum aggregating masses from the house siding. Captured bugs should be killed (freezing is recommended), otherwise they may find their way back to host plants. Keep stink bugs out of the home by caulking and sealing all cracks and crevices around doors, windows, faucets and wires. Screen attic, soffit and crawl space vents and windows. Remove, or screen window air conditioners where they get in most easily.

Management—biological control

Seventy-one parasitoids are known worldwide and there are many stink bug predators. As with any invasive pest, it is likely that outbreak conditions will exist for a few years, before natural enemies will begin to take their toll and pest numbers will drop to more manageable levels. Until then, look for light-colored, flat, parasite eggs on the exoskeletons of stink bug adults and nymphs. Set these aside so the parasitoids can hatch.

For Management—chemical control

See “True bug” in Table 1:

For further information:

See “Stink bug” in:

CABI (Centre for Agriculture and Biosciences). 2016. Nezara viridula (green stink bug). http://www.cabi.org/isc/datasheet/36282

Looney C., M. Tilbury, B. Carman, T. Murray and M. R. Bush. 2019. An Established Population of the Southern Green Stink Bug, Nezara viridula (Linnaeus), in Washington State. Proceedings of the Entomological Society of Washington 16. December 2019.

Ash whitefly (2015)

Siphoninus phillyreae  

Ash whitefly was first detected in California in 1988 and has since spread to seven states in the south. In 2014, it was detected in Oregon. Clouds of whiteflies have been seen in the late summer and fall in the Willamette Valley. The wide range of ornamental, native and fruit tree hosts make this a pest to watch for. For now, it is limited in its distribution. Early detection in new locations presents an opportunity to introduce natural enemies so that they increase along with the pest.

Pest description and damage Ash whitefly adults have translucent white wings through which the yellow body may be visible. The pale-yellow eggs are surrounded by waxy deposits. Translucent nymphs become more opaque and covered with tufts of white wax as they develop. The puparia are also covered with white wax and surrounded by tubercles exuding sticky honeydew. Infested leaves have a sticky mess of eggs, waxy nymphs, puparia and honeydew. Both adults and nymphs feed. Excessive whitefly feeding can defoliate trees, cause premature fruit drop and may lead to the death of the host plant in severe whitefly infestations.

Biology and life cycle Female whiteflies lay eggs on the undersides of the leaves on host plants. Nymphs emerge from the eggs and settle onto the leaves where they remain and feed on the plant sap. They then pupate and later emerge as winged adults. Adults live 30-60 days with several generations in a year. Adults leave preferred summer hosts such as ash, pear and hawthorn to overwinter and breed on evergreen hosts. It is not uncommon for whiteflies to linger on evergreens without developing other life stages. However, for the nursery industry they may be a contaminant the customer does not want introduced into their landscape.

Pest monitoring Watch for clouds of tiny whiteflies, or sticky honeydew and sooty mold under infested leaves.

Management—cultural control

There are no lists of resistant cultivars of plants at this time. Strong streams of water directed to the undersides of plants may dislodge or injure the various life stages. Sticky traps and screening provide some protection.

Management—biological control

Several biological control agents have been released in other states to manage populations of ash whitefly including a parasitic wasp Encarsia inaron and a lady beetle, Clitostethus arcuatus. E. inaron was the most successful agent limiting the populations of ash whitefly in California. The wasp had emergence rates from ash whitefly nymphs at 80 to 98%. In Florida, E. inaron was also found to be effective as a parasite of ash whitefly. Because the whitefly parasite, Encarsia inaron, is so effective, pesticides should be used with caution to allow the natural enemies to build up to effective numbers.

For biology, life history, monitoring and management

See “Whitefly” in:

Management—chemical control

See “Whitefly” in Table 1:

For further information:

Paine, T., Bellows, T. and M. Hoddle. 2016. Ash whitefly. Center for Invasive Species Research https://cisr.ucr.edu/ash_whitefly.html

Rosetta, R. 2016. Ash whitefly. Oregon State University Extension (http://oregonstate.edu/dept/nurspest/Ash_whitefly.html).

Banded-winged whitefly (2015)

Trialeurodes abutiloneus

The banded-winged whitefly (BWW) is still very new to the PNW. It has been detected near the gorge in eastern Oregon, and a “cloud of whiteflies with bands on their wings” was also reported near the same area of the gorge on the Washington side.

Pest description and damage The banded-winged whitefly is a native of North, Central and South America. The nymphs are similar in appearance to the greenhouse whitefly (GHW) but the adults and eggs are strikingly different: adults of BWW have two jagged bands across their wings. The cream-colored-to-yellow eggs of BWW are laid singly or in small groups with the peduncle inserted into the leaf so they lay parallel to the leaf surface; while the gray to black GHW eggs are laid in partial to full circles standing on end. The pupal case of BWW has a dark marking that is absent in greenhouse whitefly nymph. BWW feed on many herbaceous garden plants and weeds as do the greenhouse whitefly. Known host plants include 33 families of herbaceous ornamentals, weeds and the occasional shrub, with a preference for Malvaceae and Solanaceae. There are three kinds of BWW damage: 1) wilting, chlorotic spotting, leaf drop and dieback of heavily infested twigs; 2) copious honeydew and accompanying sooty mold that builds up and blocks photosynthesis; and 3) the transmission of viruses: abutilon yellows virus, diodia vein chlorosis virus, sweet potato chlorotic stunt virus and tomato chlorosis virus. Plants may look sickly due to removal of sap.

Biology and life cycle BWW reproduces about as quickly as GHW. Eggs will hatch in about 12 days in greenhouse temperatures in April. The time to complete a generation is less at higher temperatures, so populations can increase quickly. Many BWW overwinter as adults, but often all stages will be present through the winter.

Pest scouting Watch for honeydew, cast skins or adults caught in yellow sticky traps to develop an aesthetic or tolerance or economic threshold and management. Use pre- and post-treatment numbers to evaluate the effectiveness of management actions. Check traps for signs of parasitoids and withhold all but drastic sprays to give natural enemies a chance to build up.

Management—cultural control

Hose off adult whiteflies and use yellow sticky cards to reduce numbers.

Management—biological control

The following predators and parasitoids are known to attack this pest in its native states: Eretmocerus staufferi, the entomopathogenic fungus; Orthomyces aleyrodes, the predatory bug; Orius insidiosus and a variety of coccinellid beetles. Other Eretmocerus and Orius spp. are available, but their efficacy against T. abutiloneus is unclear.

For biology, life history, monitoring and management

See “Whitefly” in:

Management—chemical control

See “Whitefly” in Table 1:

For further information:

UC IPM Statewide Integrated Pest Management Program. 2016. Identifying Whiteflies (http://www.ipm.ucdavis.edu/PMG/C783/m783bpwhitefly.html)

Rose stem girdler (2014)

Agrilus cuprescens

This buprestid beetle is a pest of Rosa and Rubus spp. (domestic and wild rose, Himalayan blackberry, and raspberry). Though it is newly reported in the PNW, it seems that it has been on this continent since late 1800. This pest has been found in Idaho since 1970s and was first found in Oregon in 1994 and in Washington in June of 2014.

Pest description and damage The adult beetles are small (< 0.25 inch) metallic black to coppery buprestids beetles. The wings lie flat over the body, meeting in a straight line for half the distance before the wings part slightly towards the tail end. The round, flattened eggs are laid on the bark and covered with a protective yellow substance. The white, segmented larvae have a flattened and expanded head with black mouthparts and two spines at the tail end of its cream-colored body. There is a constriction between each of the larval segments. Pupae are 0.25 inch, shiny and white with external body features visible. Adults feed on edges of the foliage, creating a ratty appearance which could be mistaken for root weevil damage, though adult damage is not significant. Larvae hatch and tunnel from the bottom of the egg into the area just below the bark, resulting in raised spirals. They then tunnel into the pith, eventually turning and burrowing upward which causes wilting of the canes beyond that point. The hollow stem weakens the cane, causing the stem to break. This damage over several years can weaken and kill plants. Damage to the floricanes often results in stem galls and reduced fruit production.

Biology and life cycle Good biological information for this insect in the PNW is not available, but we can adapt from research elsewhere. The rose girdler has a single generation in a year. Adults mate and lay eggs in June and July, with larvae feeding through the summer and overwintering in the cane as a mature larva. When temperatures reach 55°F the insect pupates, and adults emerge in May and June (in Utah).

Pest Monitoring When moving through the fields or garden, watch for canes on roses and blackberries that have galls or spiral swellings of the bark, or wilted and/or broken stems. Watch for adults feeding on leaves in June or beat foliage using a beating sheet to capture adults.

Management—cultural control

Through winter and spring, before adults emerge in May or June, remove and destroy galled, swollen, wilted or broken canes well below the damaged area to remove larvae and pupae. Larvae can continue to develop even in broken stems on the ground.

Management—chemical control

See “Wood or Trunk Borers” in Table 4:

For further information:

Alston, D. 2015. Rose stem girdler. Utah State University Extension. Utah Pests fact sheet ENT-178-15. (http://extension.usu.edu/files/publications/publication/ENT-178-15.pdf)

Westcott, R.L., C. Looney, M. Asche. 2015. Agrilus cuprescens (Ménétries) (Coleoptera: Buprestidae), the rose stem girdler, discovered in the State of Washington, with comments on host plant associations. The Coleopterists Bulletin 69(2): 275-279. (http://www.bioone.org/doi/full/10.1649/0010-065X-69.2.75)

European chafer (2012)

Rhizotrogus majalis

This new pest is destructive to lawns in the larval stage and feeds on leaves and flowers in the adult stage. This insect has been simmering in British Columbia since its first arrival in 2001. It naturally disperses at a rate of about 10 miles per year. It has been detected near the Portland airport in Japanese beetle traps, and was detected in 2015 by a homeowner, infesting a lawn near Sea-Tac Airport.

Description and damage The adult beetle is a rather plain brown beetle in the scarab family. They are about 0.5 inch long. Males have an array of antenna that fan out like plates, but females have tiny antennae. Adults feed on a variety of leaves though the damage is not significant. It is the white grub developing in the soil under turf and sod that is of importance. Unlike the more familiar European crane fly larvae, the European chafer feed on the roots, severing the blades from the roots, while the European crane fly feeds on the grass blades. The beetle grub is white with three distinct and gangly true legs and a bulbous bag at the hind end. It has a good set of mandibles for feeding on roots. A secondary problem is roving bands of raccoons and skunks that have a family feast while destroying homeowner lawns.

Biology and life cycle European chafer has a single generation in a year. Adults mate and begin laying 20-30 eggs at dusk. The eggs hatch and larvae begin feeding on small roots and work their way up to larger roots. The larvae feed underground all winter. In May, they create a little crater to pupate in and after 2 to 3 weeks the adults emerge.

Pest Scouting Adults begin buzzing about in May-June, sounding like a swarm of bees as they feed and seek mates. Sometimes exhausted beetles are found near porch lights. To monitor for larvae, dig out a patch of sod and look for the C-shaped white grubs in the root zone of the grass. Five to 10 larvae per square foot is the trigger to take action.


Keeping turf healthy with a good root system is likely to slow the damage to the turf. With more roots to feed on, there are also more roots to keep growing while they feed. Compact, drought-struggling lawns will have a tougher time surviving.


Parasitic nematodes hold some promise for management.

Management—chemical control

See “Beetles” in Table 5:

For more information

Murray, T., G. Stahnke, and E. LaGasa. 2012. Pest Watch: European Chafer. WSU Extension. FS071E. (http://cru.cahe.wsu.edu/CEPublications/FS078E/FS078E.pdf)

Lily leaf beetle (2012)

Lilioceris lilii

The red lily leaf beetle is a European and Mediterranean beetle that is particularly fond of plants in the lily family. Known hosts are true lilies (excludes daylilies) and particularly the Asiatic lilies and fritillaries. It is also known to feed on other plants in the Liliaceae family such as Polygonatum spp. (Solomon’s seal), Smilax spp.; and on Nicotiana spp. as well as Solanum spp., such as bittersweet nightshade and potatoes. They feed on all the above ground plant parts: leaves, stems, buds and flowers; trash them with black frass; and can cause rapid death of plants.

This beetle entered North America via Montreal in 1945. In 1992, it was found in Cambridge, Massachusetts and since then has spread (and been limited) to seven east coast states. In 2012, it was found in Bellevue, Washington. This pest is most likely to have a substantial impact on the economics, markets, and pesticide use for lily bulb producers, cut flower growers, lily enthusiasts and the native host plants.

Pest description and damage The red lily leaf beetle is bright red and shiny—like red lacquer jewelry. It is 0.25 to 0.375 inch in length with black head, legs, underside and antennae. Adult beetles can stridulate (squeak) when disturbed. The eggs are also reddish when laid, then turn to a reddish-brown. Larvae are initially reddish, but later turn to a slimy black with their excrement, which they place over their back. The damage inflicted by the adults consists of chewing the leaf edges and holes in the center of the leaf. Larvae first scrape the tissue from the leaf surface turning the leaf to a slimy mush, then chew larger holes in what is left.

Biology and life cycle The red lily leaf beetle in Bellevue overwintered as an adult in ground litter and emerged with warm weather in late March. Female beetles are capable of laying more than 400 eggs in small groups. In Bellevue, they began laying their red eggs as soon as they began emerging. Eggs were laid in small clusters on the leaf surface. These hatched and the larvae began feeding. When mature (3-4 weeks), larvae drop to the soil and form a cell in which they pupate. The next generation of adults emerges in about 2-3 weeks after that. There may be more than one generation in a year.

Pest monitoring Begin watching for holes or specks of black frass on the leaves, or the red beetle adults as soon as the weather warms from mid-March, or when lilies begin to emerge from the soil. In Bellevue in 2013, beetles were found on March 25th and lilies were barely two inches out of the ground. Hand pick and squish any beetles, eggs or larvae that are found. The beetles may also hide underneath the leaves. If there are a lot of lilies of high value and early damage is severe, pesticides may be necessary. The most vulnerable stage for control is when larvae are small. Be sure to check less favored, but acceptable, hosts such other lily relatives, nightshade, nicotiana or potato. If homeowners suspect they have a lily leaf beetle, please capture an image and report your fi hic-pestshttps://agr.wa.gov/departments/insects-pests-and-weeds/insects/exotic-pests

Management—cultural control

Minimize planting lilies in contiguous plantings. Mixed plantings make it more difficult for beetles to find new host plants. Asiatic hybrid varieties of lilies are most susceptible. Oriental varieties as well as Lilium henryi ‘Madame Butterfly,’ L. speciosum ‘Uchida,’ L. ‘Black Beauty,’ L. regale and L. ‘Golden Joy’ are reported to be resistant varieties to this pest.”

Management—biological control

There are no parasitoids for this insect that are native to North America. However, parasitoids in the families Ichneuonidae and Eulophidae are known from the beetle’s native lands. Several parasitoids of the red lily leaf beetle from Europe have been imported and released in the east coast states with some success.

Management—chemical control

See “Leaf feeding beetles” in Table 2:


Murray, T.A., E. LaGasa and J. Glass. 2012. Pest Alert: Red Lily Leaf Beetle. WSU Extension.

Mountain ash sawfly (2009)

Pristiphora geniculata

Mountain ash sawfly is a recent addition to pests of American and European mountain ash, (Sorbus americana and S. aucuparia respectively), which are commonly planted ornamental landscape trees and naturalized in parks and woodlands. The insect arrived in the U.S. from Europe in the 1920s. It was first found north of Seattle in 2009 and has spread to several counties since.

Description and damage The mountain ash sawfly is a gregarious caterpillar-like larvae that feeds on the leaves of its hosts. They characteristically consume all but the rachis and midveins of leaflets leaving only a skeleton. The young larvae are yellowish and somewhat translucent. As they grow they become orange-yellow with distinct black spots. The larvae feed gregariously, lining up along the edge of the leaflets nearly head to head, and swing their tail end away from the leaf. In this position, they eat their way to the midrib, then move to new leaves. The larvae spin a brownish-tan capsule and remain as a prepupa, during the winter. When conditions are right they become pupae and then transform to the adult stage. Adults look like small dark flies (but with four wings, they are actually in the order Hymenoptera: bees, ants and wasps).

Biology and life cycle Winter is spent in the pupal stage in the soil. In late spring the adults emerge, mate, and insert eggs into slits in the leaf. These hatch and the tiny first instar larvae line up along the leaf edge and feed. They molt several times until they are fully mature, then pupate in mid-summer. There are two and possibly three generations. Pupae are reported to be able to delay emergence for two and sometimes three years.

Pest monitoring Scouting should include a periodic visual scan for larvae on leaves. Sticky traps hung from branches can be deployed to provide evidence of adult emergence. Assess the severity of the infestation. A few bunches of larvae might be ignored, but then it is important to watch for that second generation so the numbers and potential for damage can be evaluated. After observing trees that were heavily infested in one year, it is puzzling that the sawflies do not always return in the next generation or the next year. This makes it extremely important to monitor and make sure larvae are present before applying pesticides.

Management—cultural control

Prune off the clusters of sawflies when they are first noticed to reduce to minimize damage to the tree. Early removal reduces the potential for defoliation in mid-summer by the second generation. If the tree is defoliated, provide water and light fertilizer to stimulate new growth.

Management—chemical control

See “Sawfly” in Table 2:

For further information:

Granger, B. 2016. Mountain Ash Sawfly Persists in the Pacific Northwest. Pacific Northwest ISA. https://pnwisa.org/2016/08/mountain-ash-sawfly-persists-in-the-pacific-o...

Elm seed bug (2009)

Arocatus melanocephalus

The elm seed bug has limited distribution in Oregon,Washington and Idaho. It is also found in Utah. The elm seed bug is native to south central Europe. While it is not known how it arrived, there have been past interceptions at eastern seaports on imported tile from Italy. Like most introduced insects, numbers are initially low and the pest is rarely seen until numbers build over several years and it becomes epidemic.

Pest description and damage The elm seed bug is a small (0.33 inch) true bug with rusty red markings on the thorax, wings and legs, an orange underbelly, and alternating dark and white marks along the edge of the abdomen. The nymphs are brighter and reddish with a black head, similar to the related boxelder bug. Eggs are rarely noticed unless the seeds fall to the ground. Adults and nymphs thrive on the abundant seeds of elms and other trees such as oak or linden. Because they feed on seeds in the trees, they are not a major landscape pest. However, they cause concern when adults and nymphs drop onto decks, congregate on the building siding, then enter homes in prodigious numbers. This occurs in July and August as they seek relief from the heat, in fall when they are seeking winter shelter, and again in spring when they leave. Both adults and nymphs emit an unpleasant odor.

Pest biology and life cycle The adults emerge from overwintering sites in spring, mate, and lay eggs. While there is only one generation per year, the adults have an extended egg laying period and both young and adults are present throughout the summer and fall. Eggs hatch and young nymphs go through a series of molts. At each molt their wing buds become more visible until the final molt when they have fully developed adult wings.

Pest monitoring Watch for adults on house siding, or on seeds in the trees or on the ground, or on the siding of buildings during hot periods and in fall.

Management—cultural control

  • Pest proof your home including caulking of all cracks and crevices around siding, windows, doorways, faucets, or electrical fixtures, etc.
  • Remove adults and nymphs with a shop vacuum (to avoid odor contamination of your indoor vacuum) when they are congregating.
  • When the problem persists, consider removing elms adjacent to the home. Be sure that trees don’t belong to the city or a neighbor.
  • Rake or vacuum elm seeds in the fall from siding, walkways and areas where seed bugs congregate, such as firewood.
  • Inspect boxes, pots and firewood logs before bringing them inside.

Management—chemical control

See “True bug” in Table 1:

For further information:

Ellis, J. 2013. Elm seed bug, Arocatus melanocephalus: an exotic invasive pest new to the U.S. Idaho Department of Agriculture (http://extension.oregonstate.edu/malheur/sites/default/files/spring_2013...)

Stokes, B. S., E. Bechinski, & P. Castrovillo. 2016. Managing Elm Seed Bugs around Your Home. University of Idaho Extension CIS 1223. (https://www.extension.uidaho.edu/publishing/pdf/CIS/CIS1223.pdf).

Exotic Seed Bugs (2001- 2005)

Mediterranean seed bug (Xanthochilus saturnius)

Rhyparochromus vulgaris

Tuxedo bug (Raglius alboacuminatus)

There are several native seed bugs in the Pacific Northwest (PNW). Examples include the boxelder bug (Heteroptera: Rhopolidae; Boisia trivittata), the western conifer seed bug (Heteroptera: Coreidae; Leptoglosus occidentalis), some stinkbugs (Heteroptera: Pentatomidae) and many others. Between 2001 to 2005, three new seed bugs in the family Rhyparochromidae, or the dirt-colored seed bugs, have been found for the first time in the PNW. The three new bugs are the Tuxedo bug (Raglius alboacuminatus), Rhyparochromus vulgaris and the Mediterranean seed bug (Xanthochilus saturnius). There is very little known about these bugs, possibly because they are not major economic pests. They do cause anxiety among homeowners, and costly eradication expenses. Henry stated that seed bugs are frequently intercepted at port, primarily on pallets of tile and other ceramic products. Italy represents the origin of many of these interceptions.

Pest description and damage To a gardener, these three seed bugs would look rather similar. They are very small and flat, and are rapid runners. They all have a gray head with bulging compound eyes. And they occur in large numbers.

The tuxedo bug (Raglius alboacuminatus), was first reported from Utah in 1999. It is larger than Rhyparochromus and has two to three white spots, two light bands around the thorax that are visible when viewed from the side or below, banded legs and a dark abdomen.

Rhyparochromus vulgaris was first found in California and Oregon. It is similar bug has no white rings around the thorax. The legs are uniform in color and the abdomen is light-colored.

The Mediterranean seed bug, Xanthochilus saturnius, is very small with even more distinctive markings of black-on-tan. Behind the head is the thorax with a jet black band followed by a band of stippled brown. The large triangle between the wings (scutellum) is also jet black. A light stripe outlines the scutellum, and the posterior edge of the leathery portion of the wing, forming a distinct X. There are also three other jet-black blotch markings on the wings. Oregon reports “It can be very abundant in grass seed fields in southern Oregon, indicating that it does feed on grass seed.” For that reason, it continues to be “regulated in foreign trade”. Even though they do no damage to house, humans, or pets, these seed bugs become a huge annoyance and costly to exterminate when they migrate into households.

Biology and life cycle All the seed bugs overwinter as adults in gregarious clusters in protected places such as under bark or tucked in firewood, or walls of buildings. The adults emerge in spring (April or May) as weather warms, mate and lay eggs. Small nymphs look like the adults without wings. Adults and larvae feed together on the same plant or on seeds that have fallen to the ground.

The seed bugs are commonly found among tall grasses and weeds, fallow fields, and edges of woodlands, especially those areas with bare ground, where they feed on fallen seeds. Hosts that have been listed include Stachys and other Lamiaceae, and Scrophulariaceae (Verbascum lychnitis). They also feed on seeds of landscape plants such as elm, poplar, (as well as nettle, sage and raspberries.) Eggs are laid in ground liter, on the soil or on leafy or woody litter. These bugs are generally seen running about on the ground, litter or woody debris; there are few direct observations of them feeding on the plants. It is likely they simply feed on grass and weed seeds lying on the ground. The nymphs become mature adults by July and the new adults begin a second generation. These insects become a major nuisance when they move to irrigated grasses from dry pastures. They are even greater nuisance when they migrate into houses in prodigious numbers. They impact on seed production, and survival for plants and grasses is unknown. As regulated insects, they can have economic impacts to trade. They create a nuisance, anxiety and expense for homeowners. Their impact to fragile ecosystems is unknown.

Pest monitoring Their abundance in landscapes generate calls to nurseries and extension when they are encountered by gardeners or the landscape maintaining crews, or when they are become more visible on the foundation and siding of houses as they move into homes for the winter.

Management—cultural control

Management strategies are usually not needed. If the bugs become objectionable, reduce the amount of bare ground (adding groundcovers) among plantings and pull weeds before they set seed. In houses, seal up all cracks and crevices where they might enter and place screens over windows and doors. A vacuum or shop vac is very effective in removing bugs.

Management—biological control

There is no mention of natural enemies in their country of origin or here in the PNW. Likely small insectivores like salamanders, frogs, lizards and some birds are potential predators. However, these generalist predators are lacking in urban environments; and given the reports of large numbers of seed bugs entering buildings, predators that are present do not consume enough prey.

Management—chemical control

See “True Bugs” in Table 1:

For further information:

LaGasa, Eric. 2006. New Pest Alert and Update; Introduced Exotic Seed-Bugs are New and Increasing Nuisance Problems in Areas of Western Washington - Rhyparochromis vulgaris and Raglius alboacuminatus http://agr.wa.gov/plantsinsects/insectpests/exotics/surveys/seedbugs_06.pdf

Mediterranean seed bug. (http://nathistoc.bio.uci.edu/hemipt/Xanthochilus.htm)

Viburnum leaf beetle (2001)

Pyrrhalta viburni

The first record of the viburnum leaf beetle in North America was from Ontario in 1947, although it is thought to have arrived in the early 1900s on nursery stock from Europe. It wasn’t found in the U.S. until 1996 when beetles were found in New York State. The beetle rapidly spread to neighboring states of Maine, New Hampshire, Vermont, and some of Pennsylvania and Ohio. In 2001, it reached British Columbia. WSU Master Gardeners found the first Washington specimens in Whatcom County a few years later. In 2015, reports of gardeners removing viburnums killed by this beetle were not uncommon. With good scouting and timing of pesticides, or winter shearing to remove eggs deposited at the tips of branches, it should be possible to retain viburnums in our landscapes.

Pest description and damage The eggs of the viburnum leaf beetle are tucked into depressions chewed in the stem at the tips of the new growth. Eggs are then covered with a mix of chewed plant tissue and excrement, leaving visible scars on the twigs. The tiny larvae are greenish-yellow, becoming more yellow with rows of tiny black “pimples” as they mature. The pupa is small and white with some light brown on the top of the head, brown mouthparts and black eyes. The adults are drab brown and quite small (5-6 mm) but numerous on leaves. Damage to leaves is extensive and varies from brown skeletonized areas, areas of small holes between veins chewed by the older larvae, and oblong holes chewed by the adult. Trees and shrubs can be entirely defoliated. The greatest impact will be for nurseries, growers, arboreta collections, and mature landscapes.

Biology and life cycle VLB overwinters as eggs in the stems of the current season’s growth. In spring, they hatch and begin to scrape tissue from the underside of the leaf surface between the veins. As they grow, they are able to chew through the smaller veins leaving a network of holes. The mature larvae chew larger holes, then crawl down the stem to pupate in the soil. The adults emerge and chew oblong holes in the remaining leaf tissue, leaving only the midrib and secondary veins. From egg to adult may take only two months. Adults mate and the females can lay up to 500 eggs. Adults continue feeding until the first hard frost.

Pest monitoring Look for, and remove, the distinctive egg scars on the most current stems during the winter when stems are bare. When infestations are heavy, it may take shearing to remove the branch tips. As the weather warms, check leaves near the tips of twigs for the first small larvae on the undersides of leaves. Next, small holes will appear in leaves. If you wait too long, the leaves will become ratty.

Management – cultural and physical

The VLB feeds on many Viburnum species: most susceptible include Viburnum dentatum (arrowood viburnums), V. opulus (European cranberry bush), V. opulus var. americana (American cranberry bush), V. rainesquianum (Rafinesque viburnum) and V. sargentii (Sargent viburnum). However, there are a number of viburnum cultivars that are resistant to VLB. These include resistant species such as V. plicatum var. tomentosum (doublefile viburnum), V. carlesii (Koreanspice viburnum), V. burkwoodii (Burkwood viburnum), V. x juddii (Judd viburnum), V. x rhytidiophylloides (lantanaphyllum viburnum) and V. rhytidiophylum (leatherleaf viburnum). For a complete list of resistant, moderately resistant, moderately susceptible to very susceptible viburnums see http://www.hort.cornell.edu/vlb/suscept.html.

Since larvae crawl down the stem (rather than drop) to pupate, a sticky barrier or up-facing v-shape collar around the trunk may provide some control. Hand-removal should be done in the morning hours before the larvae and adults warm up and become more active. Striking bushes with a stick over a paper box lid may dislodge beetles and larvae more quickly than handpicking if they are abundant or drop them through the hole in the lid of a plastic drink container and freeze them, then dispose. Populations may be reduced in warm winters if the eggs don’t get their required prolonged chilling period.

Management – biological

While natural enemies specific to VLB are unknown in the U.S., generalist predators such as some birds, lady beetle adults and larvae, lacewing larvae and spined soldier bugs nymphs are known feed on larvae. The lady beetle adults and spined soldier bug adults also eat the adult viburnum leaf beetles. Ground beetles and insectivores also could feed on pupae in the soil and litter.

Management—chemical control

See “Leaf feeding beetles” in Table 2:

For further information:

Department of Horticulture Cornell University. 2018. Managing Viburnum Leaf Beetles (www.hort.cornell.edu/vlb/manage.html)

Murray, T., E. LaGasa, C. Looney, N. Aflitto. 2016. Pest Watch: Viburnum Leaf Beetle. WSU Extension Publication FS202E. http://pubs.cahnrs.wsu.edu/publications/pubs/fs202e/