Brown Marmorated Stink Bugs

Brown marmorated stink bugs have invaded the world!

Okay, so maybe that was a bit melodramatic, but the fact remains: brown marmorated stink bugs have exponentially increased their range and they can be serious garden pests.

Brown marmorated stink bug (OSU) CC BY-SA 2.0

The problem with stink bugs

Most stink bug species eat popular fruit and vegetable crops, such as apples, peas, peppers, as corn, raspberries, grapes, tomatoes, pecans, pears, peaches, nectarines, lima beans and other bean plants, blueberries,  hazelnuts, and cucumbers. When they feed, stink bugs inject your garden plants with enzymes that break down plant tissue into juices they can suck up. This makes the fruit under the skin tough, and pretty unappealing to us. It also sets the stage for several bacterial, viral, and fungal diseases. 

​Stink bugs also feed on buds, flowers, leaves, stems, and new bark. Since stink bug populations can grow very quickly, they can cause significant damage. [They also like to overwinter in your home.] To make matters worse, insecticides do not generally work to control stink bug populations. So, what makes the brown marmorated stink bug an even bigger problem than other stink bugs?

The traveling brown marmorated stink bug

Brown marmorated stink bugs are originally from Eastern Asia. They are believed to have first appeared in the U.S., in Pennsylvania, some time between 1996 and 2001. These pests reached the West Coast in 2004, and are now found in over 40 states. While native stink bug populations tend to be controlled naturally by beneficial predators, such as parasitic wasps, this invasive pest has few natural enemies and, as stated earlier, it tends to be unfazed by chemical insecticides. This is why it is so important to be able to tell the difference between native stink bugs and brown marmorated stink bugs.

Brown marmorated stink bug identification

Adult brown marmorated stink bugs are 5/8 inch long and a mottled brown. Like other stink bugs, they have the telltale shield-shaped body. Some characteristics unique to these particular stink bugs include two white bands on the antennae, a blunt face, faint white bands on the legs, and a banded edge around the abdomen. If you are looking really closely (and why wouldn’t you?), you will also see that the thorax (shoulder area) is smooth, and there are dark bands on the tip of the membranous forewings. The folks at UC Davis made an informative video about the differences between brown marmorated stink bugs and more common, native consperse stink bugs.

​Brown marmorated stink bug eggs are white to pale green, and barrel shaped. Eggs are normally laid in clusters on the underside of leaves, though I have also seen them laid in lines on bird netting. After hatching, nymphs go through fives developmental stages, or instars, in which they shed their skin, much the way a snake does, as it grows. Nymphs start out only 2.4 mm (less than 1/10 inch), and grow to reach 12 mm (just under 1/2 inch). Early nymphs are brown, with an orange abdomen. Second instars are nearly black, while later instars develop the characteristic mottled brown color. Initially, markings are red, then black, and finally white.

Brown marmorated stink bug eggs and hatchlings (Chuck Spidell) CC BY 3.0

Stink bug eggs on netting

​​Brown marmorated stink bug lifecycle

Each autumn, these pests gather along fences, tree trunks, and buildings. From there, they move to a protected area where they overwinter in a resting stage called facultative diapause. In the spring, these adults become active again and start feeding. Within two weeks, they mate. Soon after, females begin laying the 200 to 500 eggs she will deposit in her lifetime. In the mid-Atlantic states, there are two generations each year. Here, in California, we do not yet know the extent of the brown marmorated stink bug’s reproductive capabilities. It is safe to assume that there will be even more generations here, where winters tend to be mild.

​Managing brown marmorated stink bugs

Since insecticides don’t work, and there are few natural predators, what is a gardener to do about brown marmorated stink bugs? First, start by excluding them from your home and other buildings. Caulk openings, seal cracks, and use weatherstripping around air conditioners, doors, and windows. [This can reduce your electric bill, as well!] Next, since stink bugs are attracted to light, turn off unnecessary lights at night. [Another bonus for your utility bill.] In the case of heavy infestations, you can always use a shop vac or a handheld car vacuum to collect the little beasties. The most effective stink bug control is simply handpicking. You can drop stink bugs in a container of water with a couple of drops of dish soap, or feed the pests to your chickens.

Assassin bugs, green lacewing larvae, some parasitic wasps, and earwigs are also known to feed on stink bugs, so avoid using broad spectrum insecticides. Row covers can also be used to protect specific plants and crops against stink bug damage.