Invasive Species: Brown Marmorated Stink Bug

Brown marmorated stink bugs (Halyomorpha halys) are an invasive pest found throughout most of the continental United States. Named for the scent glands located on its abdomen and thorax, the marmorated stink bug releases a foul odor when it is threatened or injured. Native to Asia, experts believe that the species was first introduced to the United States by way of shipping containers around the mid-1990s. They are most concentrated in the mid-Atlantic region but have been identified in the majority of U.S. states and the District of Columbia.

Their presence is of special concern to farmers, as they can damage a wide range of high-value fruit, vegetable, and field crops, as well as ornamental plants. In the winter months, adult stink bugs seek shelter in homes and other structures, also causing infestations well outside of agricultural settings. While brown marmorated stink bugs aren’t dangerous to pets or humans since they do not bite or cause damage to buildings, their unpleasant scent can make large populations of bugs inside the home a nuisance.

How Were Brown Marmorated Stink Bugs Introduced in the United States?

While the species is native to China, Japan, Korea, and Taiwan, it has now also been detected in at least 38 U.S. states. It was first recorded in 2001 in Allentown, Pennsylvania. By 2003, Cornell University researchers had officially identified the Pennsylvania specimens as brown marmorated stink bugs, hypothesizing that the pests had been accidentally introduced via bulk freight containers from either Japan, Korea, or China. Free from their native predators, the brown marmorated stink bugs began to thrive in the U.S. Their quick-breeding tendencies and diverse diet helped populations spread rapidly across the country.

Regionally, there have been more brown marmorated stink bugs recorded in the Southeast and the mid-Atlantic, while the smallest numbers have been spotted in the West. Nymphs, which also cause extensive damage to crops, are observed more often during the months of July and August, while adults are more abundant from September to October.

The potential distribution of the brown marmorated stink bug isn’t limited to the United States. These pests feed on over 300 different types of plants, so they could make themselves at home pretty much anywhere. The bugs have already spread to every continent in the Northern Hemisphere, most recently to Europe, and there have been reports of interceptions in the trade and postal goods industries into Southern Hemisphere countries as well. Distribution models show the potential for even further spread throughout North America in the central and Southern states, as well as substantial risk in warm tropical, subtropical, and Mediterranean climates.

Problems Caused by the Brown Marmorated Stink Bugs

The year 2010 saw some of the worst damage caused by the invasive brown marmorated stink bug in history. That year, there were $37 million in losses to apple crops in the mid-Atlantic alone, and some growers reported losing over 90% of their yield. 2011 wasn’t as severe, largely due to an increase of broad-spectrum insecticide application throughout the region, some companies using as much as four times their normal amount of pesticides. This widespread use of insecticides was credited for disrupting integrated pest management programs, causing outbreaks of several other pests that are normally controlled by natural predator insects.

Brown marmorated stink bug feeds on both the leaves and the fruit of crops, causing them to be unmarketable as fresh products and unusable for processed foods. A stink bug will typically feed through an individual crop from the inside; for example, with corn, they pierce kernels and suck out the juices from the inside of the husk. This makes the stink bug particularly dangerous, as damage isn’t usually obvious upon initial visual inspection. Stink bug infestations tend to congregate on the edges of fields in the warmer months before seeking shelter in early fall.

As the weather cools, adult brown marmorated stink bugs shift their attention to protective wintering sites, searching for cracks in doors or windows to access different structures. In fall, they are found on the outsides of buildings or gathered by the hundreds or thousands in piles of leaves or other vegetation close by. Unlike termites, they don’t cause any visible damage to buildings, nor do they threaten people or animals through disease, stings, or bites. Still, a massive stink bug infestation inside the home can turn into a smelly situation if they aren't routinely eliminated.

Efforts to Curb Environmental Damage

The EPA and the U.S. Department of Agriculture (USDA) have approved several insecticides to help manage populations of the brown marmorated stink bug, including bifenthrin and dinotefuran. In 2011, they also approved products containing azadirachtin and pyrethrins, which are both derived from botanical ingredients. The USDA’s Specialty Crop Research Initiative also helps fund a team of over 50 researchers specifically dedicated to finding management solutions to the brown marmorated stink bug.

The widespread use of pesticides, however, is notorious for harming other important species (like pollinators) and for causing ecological unbalance in natural environments. For this reason, experts have explored alternative methods to control stink bug populations. One of these includes introducing predator bugs, specifically Trissolcus japonicus (otherwise known as samurai wasps), in regions where stink bugs are abundant. Samurai wasps are egg parasitoids, meaning they’ll replace a stink bug’s egg with its own egg, essentially controlling the population at its source.

These wasps are native to the same host region as brown marmorated stink bugs and are their main predator back in Asia, but introducing a non-native species into new territory is always risky business. Studies have shown that samurai wasps are capable of killing marmorated stink bug egg masses at a rate of nearly 80% in its native range, but finding the best places to release them has proven to be a challenge. The same study found that current lures known to attract stink bugs aren’t helpful when it comes to egg-laying, but trees with active fruit structures are more likely to have larger quantities of egg masses.

Another con to the samurai wasp plan is that there’s no way to control just what pests the predator insects decide to target. Another study showed that the stingless wasps can affect non-target species at similar (or even worse) rates, killing anywhere from 5.4% to 43.2% of bugs that aren’t invasive.

Researchers have also explored the idea of using traps instead of pesticides to control brown marmorated stink bugs. Sticky panel traps laced with an aggregation pheromone are low-cost yet inefficient, but traps with pheromone-baited cylinders with removable entry-only mesh cones have been shown to catch up to 15 times more than the sticky ones. Since the traps have removable elements, experts believe that they can also be used to sterilize insects rather than killing them.

Insecticide nets, long-lasting nets with insecticide incorporated within its fibers typically used to control malaria, have also been studied as an option for stink bug control. The idea behind this is to keep the insecticide condensed within the net so it doesn’t spread. Certain nets have resulted in a 90% mortality rate among nymphs and a 40% mortality rate among adults within just 10 seconds of exposure.