[Fall Pests] Brown Marmorated Stink Bugs

Early instar nymph feeding on the leaf of a butterfly bush in the landscape. (Photo: Paula Shrewsbury, University of Maryland)

The brown marmorated stink bug (BMSB), Halyomorpha halys (Hemiptera: Pentatomidae), is an insect known to many but loved by few. BMSB is an invasive, exotic bug from Asia that likely entered the U.S. via cargo shipments. It was first detected in the United States in Pennsylvania in the late 1990s and has since become a pest of unprecedented status. BMSB was known for years only as a nuisance pest to homeowners, but since 2010 BMSB has emerged as one of the most important agricultural pests of many crops.
 

Where are BMSB? The native range of the brown marmorated stink bug includes China, Korea, Japan and Taiwan. Since its first U.S. detection in Pennsylvania, BMSB has been detected in 33 states. BMSB has been found as far west as California and Oregon and south to Florida.

As you can see from the distribution map above, the mid-Atlantic region is the epicenter of BMSB activity in the United States. These states include Pennsylvania, New Jersey, Maryland, Delaware, West Virginia and Virginia. In several states BMSB is known only as a nuisance pest, while in others it has been detected but has not reached pest status. It is likely that BMSB populations will increase in most states to levels currently found in the mid-Atlantic region. Even if your region does not yet have problems with BMSB, you should be getting ready for it now.

        
Current U.S. distribution of the brown marmorated stink bug indicating the level of impact in various states. (map composed by Tracy Leskey, USDA-ARS AFRS)

Biology and Behaviour. Since BMSB is relatively new to the United States, there is little known on its biology and behavior in this country, thereby making monitoring and management of BMSB a challenge. What we do know is that early studies found BMSB to have one generation per year in New Jersey. In 2010, studies conducted at the USDA-ARS Appalachian Fruit Research Station determined that BMSB had two generations in West Virginia. In southern regions of China, BMSB is known to have up to six generations per year, suggesting the United States may see more generations in southern states.

BMSB adults overwinter in protected locations such as human-built structures, rocky outcroppings and under fallen trees and woody debris. In the mid-Atlantic region, BMSB adults emerge from their overwintering sites in the spring over an extended period of time (April through June), and move to plants to feed, mate and reproduce — a simple life.

Note the diagnostic white banding on the brown marmorated stink bug’s antennae. (Photo: Michael Raupp, University of Maryland)

During spring, a female lays an average of 250 eggs, which are deposited in several batches of 28 eggs on average. Immature BMSB have five nymphal stages before they reach adulthood. Eggs laid in spring by adults that survived winter complete nymphal development and become adults during late July in Maryland. These adults repeat the cycle of feeding, mating and reproducing. It is the adults of this second generation that then seek protected places to overwinter in autumn. This usually starts in early September in the mid-Atlantic. The unusual movement and dispersal behaviors of BMSB between crops and to and from overwintering sites complicate management of this pest. It moves from structures over a prolonged period of time. It feeds on more than 500 species of plants and often relocates during the growing season. It enters overwintering sites like homes over an extended period of time. This extended period of movement greatly complicates attempts to control this pest by applications of insecticides to one commodity or structure.
 

Pest Status and Damage. BMSB creates two general categories of harm to people: they are a nuisance pest in structures and they are an economic pest of a wide variety of crops. When BMSB enter homes in the fall and remain for the winter, their presence and sometimes high densities can be disconcerting to those who are not "comfortable" with insects. Tens of thousands of stink bugs have been documented inside homes in Maryland.

In addition, not all BMSB individuals settle down for the winter in homes. Homeowners are often disturbed by their constant presence, activity around lights, and "buzzing" around. When handled or disturbed, they often release a pungent defensive secretion and live up to their name of "stink bug." Given this, that is all they are — a nuisance. BMSB are harmless to humans, do not damage homes/structures and pose no risk to the health of occupants. They do not feed or reproduce indoors, although there are occasional reports of BMSB feeding on house plants.
 

On the other end of the pest spectrum, BMSB have become an extremely damaging and economic pest due to their feeding on a wide range of plant species. Numerous homeowners and vegetable and fruit producers have suffered crop losses. Apple growers in the mid-Atlantic states reported a loss of $37 million in 2010 just from BMSB. BMSB has been spotted feeding on grapes in vineyards and other small fruit. Organic farmers lost entire crops of tomatoes and peppers, and farmers suffered serious damage to corn and soybeans. Home gardeners lost vegetables from garden plots. In addition, BMSB feeds on ornamental plants from more than 56 families that include woody, perennial and annual species.
 

What Do BMSBs Look Like? Several species of stink bugs in the United States feed on plants but others are predators of pest insects. For example, the Kudzu bug is another exotic stink bug that is emerging as a significant pest in the southern United States, and also seems to be invading homes. The spined soldier bug is a beneficial stink bug that eats many kinds of pests. Therefore, it is important to be able to distinguish BMSB from other stink bugs. BMSB have a brown, marble-colored exoskeleton and a triangular shape. Most characteristic for adult and immature BMSB are dark antennae with distinct white bands.
 

Management. Pest management professionals need to know when and where to monitor, and tactics and strategies for management. BMSB will keep IPM technicians busiest in the early fall, just as stink bugs begin to move into structures to overwinter. BMSB will typically amass on the south and west sides of structures. This activity may last several weeks as bugs complete development and move from feeding sites to winter refuges. Low levels of activity may persist as stragglers move about within the house. Inside homes, BMSB activity picks up again in spring (April through June) as BMSB try to escape to the outdoors where food resources are plentiful.

There are two general strategies for managing BMSB: 1. Prevent BMSB from entering homes and structures; and 2. Reduce populations once they get into homes. Within each of these strategies several tactics should be integrated. As with all IPM programs, success will be measured by how well professionals and clients communicate and cooperate.

Before BMSB enter structures. Physical or mechanical tactics such as exclusion should be the first line of defense. BMSB enter through small gaps around windows, doors, vents, chimneys or the eves of structures. Before autumn, efforts should be made to seal cracks and crevices, and any gaps or openings to exclude BMSB. Caulk around windows, doors, utility pipes, chimneys, siding, vents and eaves; install door sweeps; screen louvered attic or soffit vents; replace or repair damaged screens; and seal or remove window-mounted air conditioning units.

We are evaluating types of landscape plants that attract and support populations of BMSB and identifying others that do not. Although our knowledge is incomplete, we believe that BMSB have a preference for vegetables and ornamental plants with seed and fruit. In the future we plan to recommend plants for landscapes that will not encourage or support populations of BMSB. Another approach that may reduce the numbers of BMSB entering homes is to vacuum them as they accumulate on the outside of structures in the fall.

Newly hatched brown marmorated stink bug nymphs aggregated around their egg mass. (Photo: Michael Raupp, University of Maryland)

Various traps are also commercially available. Some are traps marketed for use outdoors and others are used indoors. Traps may have BMSB attractants such as lights or pheromones, and also sticky substances or specific designs to catch and kill BMSB. While many of these traps catch large numbers of BMSB, there is little data on the true effectiveness of these various types of traps in reducing BMSB densities in homes or structures. Studies are underway to examine the use of traps for monitoring and controlling BMSB.

Pesticide treatment of outdoor areas, including home exteriors and/or landscape plants infested with BMSB is another approach that should reduce outdoor populations before they can move indoors. Spot treatments using microencapsulated or wettable powder insecticides can be applied in the early fall around windows, doors, ridge valleys, attic vents and other locations where stink bugs aggregate or enter homes. Note that timing of insecticide applications is critical. Applying too early will allow the insecticide to degrade before the BMSB begin to enter. Applying too late will allow stink bugs to enter the buildings.

A number of studies have been conducted in laboratories and field studies are underway to evaluate the efficacy of various insecticides. The following products performed well in preliminary studies: bifenthrin, beta-cyfluthrin, lamba-cyhalothrin, permethrin, acephate, acetamiprid, dinotefuron, chlorpyrifos, dimethoate and endosulfan. Note that this list is not exclusive, and success under laboratory conditions does not guarantee field efficacy. Also many pesticides do not have long residual activity and may not kill the insects much beyond several days. As always, read the label and follow instructions and precautions.

After BMSB enter structures. Again, physical and mechanical controls should be implemented and will be the most effective. Caulk around exhaust fans, light fixtures and other potential entry points to prevent BMSB from accessing interior rooms from basements, drop ceilings and attics. Vacuuming is the best control to remove live and dead insects that do get inside. Homeowners can also hand-collect BMSB and kill them. Drowning BMSB in a container of water seems to be effective and particularly satisfying to some. While many homeowners desire to flush stink bugs down toilets, this approach wastes large amounts of water.

The use of insecticides for BMSB in voids such as attics should only be done by professionals, and efficacy data on this approach is still lacking. In addition, treating stink bugs that are in locations where they cannot be reached and removed, such as those in wall voids or attic spaces, with insecticide may possibly result in infestations of carpet beetles or other pests that feed on the stink bug carcasses and then move onto clothing and other household items. The use of insecticides in living spaces is questionable as dead bugs still need to be vacuumed up. It may be best for PMPs to skip the insecticide and go straight to the vacuum.
 

Client Education. It is important to inform your clients that they too will have to take part in the fight against BMSB invasions. See the text box on this page and the web links below for additional information including fact sheets that you might use to inform your clients.

The author is an associate professor in the Department of Entomology, University of Maryland, College Park. E-mail her at pshrewsbury@giemedia.com.

Additional Information
For additional information on the brown marmorated stink bug, visit the following:

University of Maryland Extension information:
http://www.hgic.umd.edu/content/brownstinkbug.cfm
http://www.hgic.umd.edu/content/documents/BMSBBulletin1_10-2010_000.pdf
http://www.hgic.umd.edu/content/documents/BMSBFactSheet_10-2010_000.pdf

Pennsylvania State University BMSB Fact Sheet: http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug

Rutgers University frequently asked questions and general information: http://njaes.rutgers.edu/stinkbug/faq.asp