Stinky and Uninvited Winter Visitors

Jan 24, 2016

Brown marmorated stink bug (BMSB), Halyomorpha halys, is an invasive pest native to East Asia (China, Japan, Korea, Taiwan) which was first sighted in the United States in 1996 in Allentown, PA, and reached California in 2006 (Pasadena and San Marino). It is currently established in several regions in California including Los Angeles, Santa Clara, Stanislaus, San Joaquin, Sacramento, Yolo, Sutter, Butte, and Siskiyou counties.

Since its introduction, BMSB has spread to 38 states on the East and West Coasts, where it has caused damage to fruits, vegetables, and ornamental plants. BMSB is also a significant nuisance pest for residents and businesses, since it may invade structures in large numbers for overwintering during the fall and winter. When disturbed or crushed, this bug produces a pungent odor (hence the name stink bug), unpleasant to many people.

In autumn, when temperatures begin to drop, BMSB adults seek shelter for overwintering and aggregate under dead tree bark, rocks, or in structures such as office buildings, houses, garages, and barns by entering through openings surrounding door frames and windows, vents, and other openings and cracks.

When individual bugs find a suitable place for overwintering, they release an aggregation pheromone that attracts other individuals; this is the reason behind their large numbers within structures and on plants.

Once inside, they enter narrow spaces within buildings and stay inactive most of the time. However, on warm winter days, they may become active again and might be seen on floors, walls, or flying around lights at night. Although BMSB does not damage structures or harm people, it is a nuisance, causing residents to seek control methods.

If BMSB adults find their way into a structure, the best ways to remove them are by sweeping, vacuuming, and hand-picking. However, these activities usually disturb the adults and trigger the release of their defensive odor, which can contaminate brooms and vacuum cleaner canisters or bags, as well as the floors and walls of the structure, making it difficult to remove them, especially when present in high numbers.

Brooms can be washed after use and vacuums can be customized by attaching a paint strainer (or nylon stocking) at the tip of the tube to prevent bugs from entering the vacuum cleaner bag or canister while vacuuming. Adult BMSB are attracted to light sources, especially to white light (also black or blue light) and fly toward them at night. An excellent way to trap and kill BMSB is to fill a large pan with soapy water and illuminate it with a desk lamp in a dark room at night. The bugs will be attracted to the light, fall into the water, and drown.

The long-term control solution to BMSB management is to prevent them from entering structures in the first place. BMSB has a high dispersal capability and consequently, properties can easily become invaded by BMSB from adjacent areas. Structures close to landscaped areas and especially weedy, neglected, or abandoned land­scapes are more prone to BMSB infestations. For example, in one 2006 case in San Marino, CA, a garage adjacent to a neglected yard was invaded by so many BMSB adults that the homeowner could no longer park his car in the garage. Any time he did, the bugs would hide under the hood and when the car engine was started, adult bugs would produce their defensive odor, which entered the cabin through the vents.

To prevent BMSB from entering structures, exterior cracks need to be sealed using appropriate sealant materials such as caulk and sealant foams. Doors can be sealed using door sweeps and fitted thresholds. Gaps around window frames, pipes entering structures, and any opening on exterior walls and roofs should also be filled with an appropriate sealant material. Read more about ways to exclude seasonal nuisance pests from structures in this article from the November 2014 issue of UC IPM's Green Bulletin.

Good weed and pest management practices in gardens and landscapes surrounding structures can reduce BMSB populations from building up and invading nearby structures.

Applications of repellent insecticides may prevent BMSB from entering structures in some cases, but their effect may last only for a short time. Therefore, efficacy of such applications depends on the timing of application. Improperly sealed structures may get re-invaded in subsequent seasons by BMSB, so the best long-term solution practice is to invest resources into structural exclusion.

For more information see the UC IPM Pest Notes: Brown Marmorated Stink Bug at