Alien Invasion!

If you have a pulse and work in pest control, you’ve probably heard of the other new “bug on the block” — the brown marmorated stink bug (BMSB). These odd-looking, odiferous autumn invaders are causing panic and prayers for a solution. If you have not yet received calls about these pests, you probably will in the future. Use this article to educate yourself and your customers, and to develop a plan of action.

WHERE ARE THEY FROM? The brown marmorated stink bug, Halyomorpha halys, is native to China, Taiwan, Japan and Korea. The pest entered the United States accidentally, possibly in shipping containers. Infestations were first noticed entering homes in Pennsylvania in the mid-1990s. Specimens were initially mistaken for a native stink bug variety, but later were confirmed as an invasive species from Asia.

By 2005, the bugs had been detected in most mid-Atlantic states (Pennsylvania, New Jersey, Maryland, Delaware, Virginia, West Virginia) as well as Washington and Oregon. Today, BMSB is present in at least 43 states (Figure 1), four Canadian provinces, and some countries in Western Europe. Brown marmorated stink bug adults are strong fliers, capable of dispersing more than a mile. The bugs also are adept hitchhikers and are being transported place to place on vehicles and through commerce.

Initial reports of BMSB establishment in an area are usually when they invade buildings to overwinter. Problems associated with them being an agricultural pest occur later. Unlike the Asian lady beetle, which is considered a “cute” friend of gardeners, the brown marmorated stink bug is a devastating pest of agriculture. Crops impacted include soybean, corn, wheat, tomato, peppers, beans, squash, pecan, peach, pear, apple, citrus, cherries, berries and grapes. The bugs also feed and develop on hundreds of species of woody trees and shrubs. The list of favored hosts includes some of the most common plants in the landscape — maple, oak, ash, redbud, serviceberry, pear, crabapple, cherry, honey locust, hawthorn, lilac, etc. These ornamental hosts are capable of supporting large numbers of stink bugs in late-summer that subsequently invade buildings to overwinter.

R. Bessin and M.F. Potter.

DESCRIPTION & HABITS. Stink bugs (insect order: Hemiptera) are related to bed bugs and kissing bugs, but do not bite humans; their elongated, piercing mouthparts are used only to suck nutrients from plants. Their name comes from the pungent, cilantro-like odor produced by scent glands located on the mid-section of the body.

Hundreds of different species of stink bugs occur in North America, but only a few invade and overwinter in buildings. Most varieties are green, gray or brown and the adults, the stage entering buildings, have a shield-shaped body. BMSB adults are comparatively large — about 5/8-inch in length — and distinguishable from other stink bugs by white and black banding on their legs, antennae, and around the edge of the abdomen (Figure 2). The term “marmorated” means having a marbled or streaked appearance. As a practical matter, if clients are calling about stink bugs, chances are that BMSB is the culprit. Confirmation is important, however, since it’s easy to confuse them for other pests (Figure 3).

R. Bessin and M.F. Potter.

As noted earlier, BMSB attacks a wide variety of plants. They often feed by inserting their piercing mouthparts into fruits and seeds, damaging the marketability of many crops (Figure 4). Consequently, the pests are fast becoming a serious threat to agriculture. BMSB is also harming trees and shrubs in commercial nurseries and residential landscapes. Besides injuring berries, seeds, stems and foliage, the bugs may feed directly through the trunk, releasing sap which attracts nuisance ants and wasps.

Stink bugs lay their eggs outdoors on the underside of host plant leaves. The newly emerged nymphs are reddish and black in color, becoming brown as they mature (Figure 8). The telltale white and dark banding on legs and antennae of adults is also apparent on the nymphs. Average development time from egg to adult is about 30-45 days. One to two generations per year occur in northern and Midwestern states, while additional generations are possible further south. BMSB adults are quite mobile. They readily fly from one landscape to another and between agricultural, urban and forested areas in search of preferred host plants. These environments also afford overwintering habitat which is crucial for their survival.

R. Bessin and M.F. Potter.

OVERWINTERING IN BUILDINGS. Brown marmorated stink bugs prefer to hibernate in cool, dry, protected places. Cracks and voids within buildings fulfill these needs perfectly. Favored overwintering sites in nature include rocky outcroppings and standing dead trees with loose, thick bark such as oak and locust. The bugs do not overwinter in shrubs, mulch or leaf litter, which are generally too moist for their survival. Substantial mortality of BMSB occurs when winter temperatures routinely fall below 10oF. Conversely, mild winters (such as many areas experienced this past year) foretell of large population increases as the seasons progress.

The “urge” to overwinter is triggered by decreasing day length and temperature. Late in the summer, adults congregate in large numbers on favored host plants. When the aggregations occur close to buildings, subsequent movement indoors is likely. Dwellings in wooded and agricultural areas are especially prone to stink bug invasions, as they are to invasion by lady beetles. Similar to lady beetles, adult stink bugs move to buildings on warm sunny days in September and October.

Flight activity tends to be greatest in the afternoon and may vary in intensity from one day to the next. After the bugs alight, they seek out protected places to spend the winter. Common entry points include cracks and gaps around windows, doors, roof flashing, vents, window air conditioners, fascia and siding. They tend to prefer upper areas of buildings, often entering via attics and chimneys. A similar preference for higher locations occurs in nature, where the bugs choose upright trees over fallen ones and ground litter.

Buildings in poor repair with many cracks and openings are most vulnerable to infestation. In such cases, stink bugs may enter by the thousands (Figure 5). Overwintering locations include crevices, walls, ceilings, and attics affording cool, dry refuge. Unheated attics are often the most crucial overwintering location inside buildings; crawlspaces and basements are much less preferred. Stink bugs also overwinter in garages, outbuildings, vehicles, HVAC units, gas grills, etc.

R. Bessin and M.F. Potter.

During winter and early spring, stink bugs again become active, accessing living areas through cracks, vents, fireplaces and other openings. While the overwintering habits of BMSB and Asian lady beetles are similar, there are some differences. Stink bugs begin entering buildings earlier in the fall — early-mid September, vs. October/November for lady beetles. Stink bugs also tend to be more active indoors throughout the winter, especially on warmer days. Occasionally they may be found on houseplants, possibly feeding, in late winter. The bugs emerge from hibernation from March to May and resume living outdoors. They typically require a few weeks of feeding on host plants before mating and egg laying.

IMPACT ON HUMANS. Stink bugs are solely plant feeders and do not bite humans or pets. The adults overwinter in an unmated condition and do not breed or reproduce indoors. Consequently, those spotted during the winter are the same individuals that entered the previous fall — be sure to communicate these facts to customers. Nonetheless, clients tend to be much less tolerant of stink bugs than they might be of lady beetles, which are smaller, “prettier,” and more recognizable/better understood. BMSB are attracted to light and may buzz around light fixtures in the evening when customers are watching television or reading the newspaper. On evenings in late-summer/fall, the bugs are also attracted to porch lights, late-night convenience stores, service stations, manufacturing plants, etc. Similar to bed bugs, their fecal spotting can stain walls, curtains, and other surfaces.

Besides being a nuisance, stink bugs emit a pungent odor similar to cilantro when picked up or disturbed. When crushed, squeezed or handled they often excrete chemicals irritating to the skin. People disposing of stink bugs should be advised to use paper towels or tissue when handling them, and avoid touching their face or eyes. Recent clinical studies also suggest BMSB may be an important airborne allergen to people. Customers plagued by stink bugs may suffer irritation and inflammation of the eyes and nose, similar to the reaction some people have from exposure to the Asian lady beetle.^2,3 People experiencing such symptoms in dwellings with many stink bugs should consult their physician.

MANAGEMENT. Management options are similar to those for other fall invaders, but there also are other important considerations, outlined below.

R. Bessin and M.F. Potter.

Indoor Removal. The best way to remove stink bugs indoors is by hand (with gloves or tissue, per the point above about irritating secretions), or with a broom or vacuum. Disturbed bugs are likely to release an odor, so brooms and vacuums may smell like stink bugs for a while before the odor dissipates. A cut-off nylon stocking can be used in the suction tube of the vacuum to limit odor and conserve bags. Large collections may warrant disposal of the entire vacuum bag and aeration of the hose. Stink bugs immediately drop from vertical and overhead surfaces when disturbed. Small numbers of bugs residing on walls, ceilings, drapes, lampshades, etc. can be dispatched efficiently by placing a container underneath and gently prodding them to drop off.

Sealing Entry Points. Sealing cracks and openings is the most permanent way to prevent stink bugs and other fall invaders from entering buildings. Summer is the best time to do this, before they begin entering buildings to overwinter. Despite their relatively large size, adult BMSB are thin-bodied and able to fit into surprising tight spaces. Cracks should be sealed around windows, doors, soffits, fascia boards, pipes, wires, etc., with caulk or other suitable sealant. Don’t buy a cheap caulking gun. Features to look for include a back-off trigger to halt the flow of caulk when desired. Silicone or silicone latex caulks that dry clear are easier to use than pigmented ones because they hide mistakes.

R. Bessin and M.F. Potter.

Repair damaged window screens and install screening behind attic vents, which are common entry points for stink bugs. Trials by our lab indicate that conventional-sized, galvanized mesh hardware cloth is ineffective for excluding brown marmorated stink bugs. When adults were challenged with ½ and ¼-inch diameter mesh screening, 100 percent and 50 percent of bugs, respectively, were able to pass through the openings. Mesh sizes of 1/6 or smaller were required to keep the adult stink bugs out (Figure 6a and 6b). Also remind clients to seal or remove window-mounted air conditioners in the fall, as these are another common entry point for stink bugs.

Traps. Pheromone-laced aggregation traps are being developed and deployed for detection of BMSB and monitoring their levels in agriculture. Unfortunately, the same traps were recently found to be ineffective at attracting stink bugs during their fall through spring overwintering period within buildings. The reason for this is that the bugs do not respond to their aggregation pheromone until later in the spring after the days have lengthened. Whether future modifications of such traps will have utility in and around homes and buildings is still to be determined. Similar to lady beetles, stink bugs are strongly attracted to ultraviolet light. Consequently, glue board-based light traps can be useful for harvesting these pests in areas such as attics. Householders can fashion their own stink bug trap by positioning a light above a large pan of soapy water.

Insecticides. Insecticides are not warranted for controlling stink bugs indoors, except perhaps as an ultra-low volume (ULV) treatment of a heavily infested area such as an attic. Efforts to kill overwintering stink bugs in wall voids is unlikely to be successful, and could exacerbate problems with carpet beetles and other dermestids feeding on accumulations of dead insects.

A better approach with insecticides is as an exterior barrier treatment. For structures prone to autumn invasions of stink bugs, exclusion can be supplemented by outdoor application. Studies to date have mainly evaluated insecticides on stink bugs in agriculture. Findings suggest that pyrethroid, neonicotinoid, and pyrethroid-neonicotinoid combinations are effective, but only last about a week when applied to plant surfaces.

R. Bessin and M.F. Potter.

Preliminary tests by our lab evaluated professional products applied to bricks. Adult BMSB collected in late summer were confined on one-day old deposits of Demand, Talstar, or Suspend Polyzone. (Figure 7). Two different exposure times were evaluated, five minutes and 24-hours — based on the tendency for stink bugs to land on exterior surfaces and crawl about for a while before finding and entering a crevice or other opening. After each exposure interval, the bugs were transferred to untreated containers and observed for mortality. Five minute and 24-hour exposures, respectively, resulted in 60 percent and 100 percent mortality, suggesting it is possible to kill BMSB residing on exterior treated surfaces before they enter buildings. Labeling/usage of pyrethroid barrier sprays has gotten more restrictive, but treatment of crevices and as a targeted band around windows, doors, eaves, soffits, attic vents, chimneys, and other likely points of entry is generally permissible (read and follow label directions carefully). As with other fall invaders, the key is to initiate treatment before the bugs begin gathering on buildings to overwinter — early-mid September in the Midwest but somewhat variable by locale. Such application would probably need to be repeated at least monthly during the extended flight period of bugs to buildings.

While BMSB can feed on hundreds of different host plants, certain varieties in the landscape are preferred. Examples include redbud, maple, honey locust, serviceberry, crabapple and cherry. Pest managers can play a useful role by monitoring such favored hosts in late summer, before the bugs begin moving to nearby buildings. Companies licensed to treat trees and shrubs in the landscape can also preemptively spray aggregations of stink bugs staging in these areas near structures.

Tom Myers

FUTURE PROSPECTS. Like many invasive species entering the U.S. from abroad, the brown marmorated stink bug is expected to worsen over time. Fewer natural enemies (predators, parasites, pathogens) occur in this country to keep BMSB populations in check. In Asia, more natural enemies of the pest have been identified and efforts are underway to evaluate their suitability for release in this country. A tiny wasp which attacks BMSB eggs in China has recently been discovered in several locations in the U.S., and may provide some relief in the future.

Researchers are continuing to evaluate pheromone-based traps to aid in detection of infestations in agriculture. There’s a chance that similar traps could be developed for use around homes or buildings if one day proven effective (which remains to be seen). In the meantime, there is no simple way to prevent stink bug invasion of buildings. Vacuuming, pest proofing and properly timed exterior applications can provide relief, but require effort. Pest managers should take the lead as educators and be prepared to offer options based on the needs of the client.

2 The brown marmorated stinkbug as a new aeroallergen. 2012. J. Allergy Clin Immun. 130(4):999-1001

3 Ladybugs are a new source of allergy. 2006. Pest Control. 74(3): 57-63.

Michael F. Potter and Ric Bessin are extension entomology professors at the University of Kentucky.