EMERGING PEST: Brown Marmorated Stink Bug-A Threat to Pacific Northwest Agriculture

Nik G. Wiman and David M. Lowenstein
Latest revision: 
March 2017
Image of Brown marmorated stink bug nymphs (Halyomorpha halys) on ‘PrimeArk45’ primocane-fruiting blackberry fruit in September.

Brown marmorated stink bug nymphs (Halyomorpha halys) on ‘PrimeArk45’ primocane-fruiting blackberry fruit in September.

The brown marmorated stink bug (Halyomorpha halys) has been established in the eastern United States since the mid-1990s. This insect is an extremely invasive and damaging crop pest because it feeds on a wide-range of plants, has strong capacity for dispersal, and populations increase rapidly. It is also a nuisance pest when it overwinters inside houses in large numbers. The brown marmorated stink bug (BMSB) was first observed in the United States in Allentown, Pennsylvania, in 1996, and has since spread to more than 40 states. It was discovered in Portland, Oregon in 2004, and in Vancouver, Washington in 2010. From Portland, it has spread south and is now present in all counties in the Willamette Valley, most recently establishing in Linn, Benton, and Lane Counties. There has also been eastward spread of BMSB from Portland along the Columbia River, and populations are now established in Hood River and Wasco Counties. There have been detections in Gilliam County, and populations are now established in Deschutes, Umatilla and Union Counties. In Southern Oregon, BMSB has been detected in Douglas and Josephine Counties, and is established and increasing rapidly in Jackson County. In Washington State, BMSB has become established in Benton, Clark, Cowlitz, Franklin, Lewis, Skamania, Klickitat, Thurston, Walla Walla, and Whatcom Counties. It has also been detected in Yakima, Chelan, Douglas, and Spokane Counties. Populations of BMSB have recently been found in the Puget Sound region in Washington including: Snohomish, King, Pierce, Skagit, and Kitsap, and nuisance problems have been reported from the Seattle area. Agricultural problems from BMSB in the Pacific Northwest region have been most evident in the northern Willamette Valley. The Columbia Gorge, Walla Walla Valley, and Applegate Valley are also considered to have high risk for crop invasion at this time. Nuisance problems can be severe anywhere BMSB is established. Nuisance problems encompass damage to noncommercial crops such as backyard fruit and vegetable gardens, aggregation on homes and other structures in the fall, and infestation of homes during winter. Nuisance problems are particularly severe in the greater Portland and Eugene areas and nearby communities, as well as in Vancouver, Washington.

Pest description and life cycle

Adult BMSB (Hemiptera: Pentatomidae) are approximately 17 mm long, generally brown in color on the back, but coloration on the abdomen is variable, and can be gray, yellow, green, or red when viewed from below. The distinct white bands on the otherwise darkly colored antennae are a key character for identification. They also have alternating dark and light bands on the dorsal (top) part of the abdomen that protrudes out beyond the folded wings and dark bands on the tips of the membranous sections of the wings. Male BMSB are smaller than females and have a small notch in the distal end of their abdomen. BMSB looks similar to two other genera of stink bugs, Euschistus spp. and the rough stink bug Brochymena spp., but can be distinguished by a smooth anterior (forward) margin of the thorax (shoulder) while the other species have rough anterior margins on their thorax. The five immature stages of BMSB get larger and look more like the adult after each molt. The first instar is the smallest immature motile stage at about 2.4 mm in length. The fifth instar is approximately 12 mm in length. Immature BMSB have deep red eye color. Stink bugs have glands that emit a pungent aroma that resembles cilantro when they are disturbed or crushed.

Adult BMSB overwinter in protected areas such as houses, outbuildings and outdoors in sheltered locations. When the weather warms up in the spring, BMSB will leave their overwintering sites and disperse to vegetation to feed and reproduce. Adults and immatures readily attack fruit trees such as apple, pear, peach and cherry, particularly when fruit is present, but will also attack wine grapes, and small fruits such as caneberries and blueberries. They will also feed on nut crops such as hazelnut (Corylus avellana). Many ornamental species are important host plants, such as catalpa (Catalpa speciosa), tree-of-heaven (Ailanthus altissima), female English holly (Ilex aquifolium), various maples (Acer spp.), lilac (Syringa spp.), mountain ash (Sorbus aucuparia) and empress tree (Paulownia tomentosa). BMSB will feed on developing buds, fruit, trunks of thin-barked trees such as maple and peach, through ears of corn, peppers, tomatoes and a wide range of other plants. The eggs are laid in clusters ranging in number from 25-30 eggs per egg mass (28 on average), are typically blue-green and are attached to the underside of leaves. Eggs are most easily detected on broad-leaf hosts (e.g., Catalpa, Paulownia). After the eggs hatch, immature BMSB will molt five times as they grow and turn into an adult. Two generations per season can occur in Oregon.

The BMSB, like other plant-feeding stink bugs, damages plants during feeding. All nymphal stages and adults can cause damage except for the first instar nymphs, which feeds on its egg mass. Stink bugs feed by inserting their stylets into plant tissue, secreting digestive saliva, and then extracting the plant fluids. The extraction of plant fluids following the injection of the saliva results in deformed plant parts, loss of turgor and occasionally aborted plant ovaries. It is frequently observed that BMSB feeding on fruit and vegetables results in pithy, loose cell textured tissue surrounding the feeding site. BMSB feeding on apples close to harvest may not readily show apparent damage. However, damage is manifested during storage so that apparently undamaged fruit comes out of storage full of brown spots. Damage to fruits and nuts will not be apparent without cutting away the skin of the fruit or the nut surface. BMSB damage can be distinguished from plant physiological problems or nutrient deficiencies by the observation that pithy corking damage is always within 1 mm of the fruit surface. See https://catalog.extension.oregonstate.edu/em9054 for a printed BMSB identification guide.

Sampling and Management

During the summer and fall months, BMSB can be sampled several ways. The best ways are to just visually look for adults, nymphs, and egg masses on the crop or use beating trays or sweep nets to collect them from plants. Timed visual observations or other metrics of effort—such as the number of sweeps or beats—can help standardize samples. Pheromone traps are available commercially, but are marginally effective over most of the season. Traps work best in the late summer and fall months in areas where BMSB are present. Interpretation of trap data is limited to presence or absence data at this time as it is unclear how trap catch relates to density or damage potential. See https://catalog.extension.oregonstate.edu/em9138 for more information on sampling.

There are currently no established treatment thresholds for BMSB but given the severity of damage that occurs when populations are noticeable, growers readily spray insecticides. Current insecticide programs in the eastern USA are based upon pyrethroid, carbamate, organophosphate and nicotinoid insecticides. All of these insecticides are disruptive to various natural enemies and have the potential to cause secondary pest outbreaks. Gardeners and growers with small plots may be able to exclude BMSB with fine netting, but this is not feasible for larger farms.

Generalist arthropod predators can feed on BMSB egg masses. Biological control may become more common due to the arrival of samurai wasp (Trissolcus japonicus), a parasitoid wasp that attacks and parasitizes BMSB eggs. Wild populations of the wasp were first recorded in Vancouver WA in 2015 and in Portland OR in 2016. Although only detected in urban areas, it is expected that samurai wasp’s range will expand. Wild populations have also been reported in several northeastern and mid-Atlantic states. The samurai wasp has a parasitism rate of approximately 60-70% in its native range of China. Adults are 1.5 mm, black, prefer shaded areas, and have been spotted on BMSB egg masses laid on ornamental trees including maple, hawthorn (Crataegus spp.), and boxelder. Although the wasp’s small size makes it difficult to detect, several signs indicate the presence of samurai wasp or other parasitoids. Wasps can be recognized by their “guarding behavior” – walking and laying eggs on BMSB egg masses. Parasitized egg masses will turn a dark black color after 3-5 days. After parasitoid emergence, eggs have uneven circular holes.

This pest will also overwinter in homes. During the fall, BMSB congregate on sides of houses and buildings. They then work their way into the buildings through cracks and other openings. They can be in a semi-dormant state during most of the winter, but warm spells cause them to move around and become more noticeable. The best way to prevent them from entering homes is to seal all the openings with caulking or other material to exclude them. Once in the house, vacuuming them is the best way to capture and remove BMSB. Crushing them can cause them to release their defensive aroma, which is disagreeable and lingers for a time.

For further information and to report BMSB:

Brown marmorated stink bug. Oregon State University. http://agsci.oregonstate.edu/bmsb

Brown marmorated stink bug. Washington State University. http://www.tfrec.wsu.edu/pages/bmsb/Home

Management of brown marmorated stink bug in US specialty crops. http://stopBMSB.org