Invasive Species: Brown Marmorated Stink Bugs
The brown marmorated stink bug (BMSB) is an invasive insect relatively new to California, and the whole United States. The BMSB has caused major problems in other areas and is a threat to California.
Over 50 stink bug species occur in California—some native, some invasive. Most feed on plants and can cause significant damage, particularly to fruits and nuts. At least one stink bug species (the rough stink bug) is instead a predator of caterpillars and other insect larvae, and is considered a beneficial insect. All stink bugs, true to their names, emit an unpleasant odor when disturbed or crushed.
The BMSB species shares the “shield” shape of many stink bugs, with a rounded rear end. BMSB is about ⅝-inch long and is a marbled brown.
How did it get here, and where is it now?
The brown marmorated stink bug is native to eastern Asia—China, Korea, Japan and Taiwan. The first established population of BMSB in the United States was recorded in Pennsylvania in 2001. Brown marmorated stink bug was accidentally introduced, likely in a shipment from overseas in the late 1990s.
The brown marmorated stink bug has spread very quickly, partly due to its habit of riding long distances in vehicles or as stowaways when furniture or other articles are moved. Most new infestations are found in urban areas. As of 2021, BMSB had reached 47 states and 4 Canadian provinces. In 2022, Oregon experienced a significant increase in BSMB, with serious damage to agriculture, in particular hazelnut orchards.
In California, reproducing populations have become established in more than 15 counties; isolated BMSBs have been detected in Alameda County, and many other counties.
What harm does the brown marmorated stink bug do?
Brown marmorated stink bugs cause harm both outside and inside.
In the garden
The brown marmorated stink bug feeds on the surface of fruits and vegetables, causing small damaged spots on fruit and leaf surfaces and “cat-facing” (an unsightly dimpling, deformity, and scarring) on fruit. The damaged surfaces may also lead to secondary infections. In the mid-Atlantic, some backyard gardeners lost all of their susceptible crops to BMSB. The extent of possible damage to California gardens and home orchards remains to be seen, as the damage may differ depending on climate and host plants. Tomato, pepper, grape, apple, pear and citrus are thought to be at risk to BMSB in California. The potential BMSB host range is even wider.
In the home
BSMB, unlike other stink bugs, loves to overwinter inside homes, where it is warm and dry. It’s very disconcerting when large numbers of BMSB decide to winter in your home. They enter through cracks around doors, windows, screens and window air conditioners. They then hide in cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. They prefer high and cool locations. Here’s a story from the New Yorker (PDF) about when thousands of brown marmorated stink bugs invaded one home.
What Can I Do?
Keep an Eye Out and Report
Agriculture officials welcome reports from the public about sightings of BMSB in Alameda County. But how do you know if the stink bug you’ve found is the Brown Marmorated Stink Bug rather than another species? Among the stink bugs, the BMSB closely resembles the Rough Stink Bug and the Converse Stink Bug.
Features that help distinguish among different types of stink bugs
| Brown Marmorated | Rough | Consperse | |
|---|---|---|---|
| Antennae | White bands on antennae | No bands on antennae | No bands on antennae |
| Forward edge of head | Blunt | Has two points | Bluntish |
| Shoulders (thorax) | Smooth | Rough with protrusions | Smooth |
| Abdomen | Banded edges - light and dark | Banded edges - tan and dark | No prominent banding |
| Legs | Marbled with single light band | Two white bands on back legs | Small black spots on legs |
If you see a BMSB in Alameda County, you can report it to the state Department of Food and Agriculture:
- Through the web at https://reportapest.cdfa.ca.gov/
- By completing and submitting the Report a Pest Sighting form
- By calling the Pest Hotline at 1-800-491-1899
Tips for submitting:
- Before calling, check the Report a Pest Sighting form to see what information is needed.
- Take photos and record detailed information on where you saw the pest.
BMSB in Your Garden
Garden management for BMSB is like that for other plant-eating stink bugs:
- Row covers can be useful. A row cover is a light material that rests on top of the crop, permitting light and moisture to permeate but preventing insects from feeding on the vegetables underneath it. If the crop requires pollination, however, the row cover will need to be removed to permit the pollinators to reach the crop, and that may also allow stink bugs to feed or to lay eggs on the crop. Also, large fruit trees are very difficult to cover because winds can tear the material and in hot climates heat can build up inside.
- Because stink bugs are large, handpicking can remove them. Note that if you disturb or crush a stink bug, it will release a noxious odor that indicates how it got its name. After handpicking, you can drop them into soapy water. Check inside dense foliage and fruit clusters.
- Regularly using a hand-held vacuum dedicated to catching stink bugs can reduce their numbers. (The bugs will cause the vacuum to stink too badly to use for other purposes.)
- Check the underside of leaves for egg masses and destroy them.
- Insecticides have not been found effective, so are not recommended.
BMSB in Your Home
- The critical initial action is to seal off any access points that the BMSB may use to gain entry into your home. Seek out places insects could enter. Repair screens, and install weather stripping around sides of doors and tight-fitting sweeps or thresholds at the bottom of doors. Caulk up spaces around windows, pipes entering from outside, window air conditioners, and other entry points. Consider screening the inside of attic vents.
- Stink bugs are attracted to lights, so take advantage of this:
- Avoid lights near doors (both external and internal) when you are going to open the door.
- Trap BMSB inside by filling a basin (maybe a foil roasting pan) with water and a small amount of dish soap. Mix it to make a few suds. Point a light into the pan, and darken the room. The BMSB will be attracted to the light, fall into the water and drown. Here’s a short video demonstrating this trap. You may need to repeat this to get all of them.
- A hand-held vacuum works well to collect up BMSB inside as well as outside. Because the disturbed BMSB will cause the canister to stink, consider dedicating a separate vacuum to them or using a nylon stocking inside the tube (secured to the outside with a rubber band) so that you collect them inside the stocking instead of the vacuum cleaner canister.
- Using insecticides outside the home at entry points may work temporarily, but the sprays break down rapidly and lose their effectiveness. Sealing up is much more effective. Indoor insecticides are not recommended.
Our native parasitic wasps have not provided enough control of this new host, but parasitic wasps from Asia are being studied to see if they can provide effective biological control here. In the meantime, we can all help by keeping alert, reporting any BMSB sightings, and managing any brown marmorated stink bugs in our homes and gardens appropriately.
Resources
Watch out for the Brown Marmorated Stink Bug! (From the UC Master Gardeners of Butte County blog)
Stop BMSB research collaboration website
Have a gardening question? We'll help.
Visit our Help Desk page to submit your question and see additional ways you can reach us.