Brown Marmorated Stink Bug
Fall means different things to different folks. For some, it’s football and fall foliage season, for others it’s the time when they start anticipating the holidays with its shopping and gatherings. For gardeners, it’s performing those final fall chores: harvesting, adding that protective layer of mulch around flower beds, and annual lawn feeding. But in recent years, fall has become the harbinger of a troublesome event — the annual migration of the brown marmorated stink bug (Halyomorpha halys), from the surrounding trees and plants to the sides of our homes, from which these bugs launch their annual home invasions. This migration begins around September 21st and continues through the middle of October.
The brown marmorated stink bug, (“BMSB”) — generally refered to as simply “The Stink Bug” — is a grayish brown bug about the size of a dime (3/4 inch long) with the typical stink bug “shield” shape; it is almost as wide as it is long. The adults are marbled brown in color, with white bands on the antennae and legs. This white banding distinguishes the adults from the native stink bug species. Young (nymphs) BMSB lack wings, and have reddish and white marking on the upper surface of the abdomen.
The brown marmorated stink bug is an invasive insect not native to North America. It was accidentally introduced near Allentown, PA in 1996 and has spread since that time. It was found in Virginia in 2004 and by 2010, it was found throughout most of the Commonwealth. Today the BMSB is found in 43 states and two Canadian provinces. Unfortunately, Virginia is the epicenter of this invasion.
The BMSB will feed on just about anything. They attack trees, ornamental plants, vegetables, fruits and agricultural crops. There are approximately 120 wide ranging plants that the BMSB has been observed (and documented) feeding upon. Many of these plants are the same ones preferred by humans — especially our favorite vegetables: beans, tomatoes, peppers, cucurbits, and sweet corn. They also feed on various fruits, including apples, peaches, raspberries and brambles. High densities of this pest species have also been found on soybeans and corn crops. However, so far in Virginia, the most severely damaged crops have been the tree fruits (apples and peaches). In addition, the BMSB buffet includes many ornamental trees: crabapple, persimmon, catalpa, walnut, maple, sweet gum, red bud and American holly. One of its favorites is the tree of heaven (Ailanthus) — which is itself an invasive plant from Asia. Ornamental shrub hosts include butterfly bush, serviceberry, pyracantha, rose and honeysuckle. For homeowners, it is mainly a nuisance pest, as it invades houses in the fall looking for a place to over-winter. For businesses such as hotels, restaurants and other commercial settings with public interface, the presence of high numbers of these bugs in the fall can have economic consequences.
The Successful Invasion
There are a number of factors that have contributed to the success of the BMSB’s colonization of America — the lack of specific natural enemies, its ability to reproduce in large numbers, its wide host plant range, resistance to cold weather, effective overwintering strategies, plus the impact of climate warming. In addition to their survival attributes, the BMSB is highly mobile; it can fly up to 70 miles per day. They are also efficient hitchhikers; they’ll hitch a ride on ships, trucks, RVs, and cars, and will hide in cargo containers, packages, and suitcases.
The Life Cycle of the BMSB
Adult stink bugs overwinter in the adult stage, often seeking shelter inside houses and other buildings. Once inside, they congregate in attics, closets, walls, nooks and crannies — almost anywhere — but it’s important to remember that they do NOT reproduce inside, nor do they cause structural damage inside homes. They do not bite people or pets. Although they are not known to transmit disease or cause physical harm, the insect does produce a pungent, malodorous chemical, and when the bug is handled, the odor is transferred readily. In our area they also overwinter in natural settings, including dry crevices in dead, standing trees with thick bark, particularly oak and locust trees.
Adults emerge from their overwintering sites and head outdoors in the spring, usually early May. After they feed for about two weeks, they mate, and the females begin to lay eggs in clusters of about 28 eggs on the undersides of leaves. About 9 to 16 batches, or a total of 234 to 416 eggs, are laid over a period of two to three months. The eggs hatch in about 4 to 7 days. The nymphs feed on fruits and seedpods and pass though five “instar” stages (immature sub-stages of development) with a molt between each instar stage. Each instar stage lasts about one week, before the final molt into the adult stage. New adults start to appear in late summer. Warmer temperatures allow time for the development of more than one generation. There are from one to two generations here in Virginia. We are lucky, as even more generations have been reported in their native Asian range.
Life Cycle of the Brown Marmorated Stink Bug
Stink Bug Damage
The BMSP is highly mobile and can switch hosts, moving from plants with early-ripening fruits to those of late-ripening fruit. Because it has a broad range, almost any crop that has fruit is at risk of attack. The BMSP bug feeds by sucking juices with its straw-like mouth parts (stylets) to feed on internal plant tissues.
Feeding injury to beans may result in scarred, faded, sunken areas and deformed pods; similar pod injury can occur when bugs feed on okra. Injury to fleshy fruit like tomatoes and peppers will produce white spongy areas of the skin and internal tissue damage. In addition to direct damage, the stylets (mouth parts) can transmit pathogenic bacteria and yeast, which can cause fruit to rot. BMSB appear to feed on developing kernels of corn by piercing the husk, and the resulting damage discolors and shrinks individual kernels. Vegetable and fruit trees located nearest overwintering shelters or directly bordering wooded areas are at the highest risk of attacks.
Feeding injury from BMSB to stone fruit, principally peaches and nectarines, causes depressed sunken areas, called “cat facing” in the trade. On apples, feeding results in indented depressions on the surface and corky spots in the flesh of fruit.
Internal and external injury on apples (Photo Source: USDA) and peaches (Photo Source: StopBMSB.org) caused by BMSB feeding.
Since the widespread outbreak in the mid-Atlantic in 2010, chemical control has been the widely-used strategy for managing the BMSB. Active ingredients that have been most effective include several pyrethroids (bifenthrin, permethrin, fenpropathrin and beta-cyfluthrin) and neonicotinoids. Unfortunately, these insecticides are generally broad-spectrum in their activity. In past growing seasons, tree fruit growers increased the number of insecticide applications, in some cases up to fourfold. Since these insecticides are not insect-specific, they also kill beneficial insects as well. Because of the depletion of beneficial insects, secondary outbreaks of aphids and scale insects have increased. Thus, the increased use of insecticides has been disruptive to integrated pest management programs (IPM).
Biological control is the beneficial action of parasites, pathogens, and predators in managing pests. A common biological control most gardeners embrace is the lady bug — more properly, the lady beetle — which wages war on aphids.
However, biological control isn’t always so effective or prompt as we would like. In some cases, decades can pass before any results are noticed. A classic example is Entomophaga maimaiga, a common disease in gypsy moth populations in their native county of Japan. When scientists realized that this fungus might help control gypsy moth outbreaks in the U.S., this natural enemy of the gypsy moth was released near Boston in 1910. Fingers were crossed and breaths were held as the scientists waited for the results to come in. Much to their dismay, the expected results didn’t materialize, and the research program was abandoned. Fast forward to 1989, almost 80 years later, when much to the science community’s amazement, the fungus popped up in several northeastern states and caused a high mortality rate in many gypsy moth populations. Sometimes it just takes time for things to click and a new balance to be achieved.
Now don’t get too excited, but we may not have to wait 80 years to check the population explosion of the BMSB, as there is evidence suggesting that our native predators have developed an appetite for the BMSB and may be having a greater impact on the BMSB population than previously thought. Recent observations of BMSB egg masses revealed that they were being eaten by predators. The katydids and ground beetles are the most aggressive chewers of BMSB eggs, followed by earwigs, jumping spiders, and crickets. In addition to the predators who eat BMSB eggs, spined-soldier bugs, assassin bugs, damsel bugs, minute pirate bug mantis and grasshoppers have all been observed to eat the actual bug, at least in some of its developmental stages! However, it has been estimated that destruction by predation and parasitism averages only 5-10% percent on organic farms and does not provide sufficient control of high populations of BMSB.
As evidence mounted that the local predator population was unable to control the BMSB, a search was conducted in the native habit, eastern Asia, to find a native predator. A small wasp, Trissoicus japonicus, about the size of a comma, was identified as the leading candidate. The Trissoicus japonics wasp is an egg parasitoid, which is just a fancy way of saying the wasp lays its egg in the BMSB egg, and when the wasp egg hatches, the baby wasp eats the contents, destroying the BMSB egg. The mortality rates have been reported to be as high as 80% in China. The USDA imported the wasp to quarantine facilities for evaluation as a potential biological control agent.
Images of the tiny Trissolcus Japonicus wasp
The wasps were placed in quarantine to insure that they were specific predators to the BMSB and would not throw the balance of nature out of whack. Well, sometimes the best laid plans go awry. Before the research was completed, and prior to any release of the wasps from quarantine, “wild” populations of the tiny wasp were discovered in Beltsville, Maryland, in 2014, and in Winchester, Virginia and Vancouver, Washington in 2015. DNA testing was performed, and it was determined that none of the wasps found in the wild originated from the wasps held in quarantine! The origin of the wild wasp population is unknown, but it is speculated that, just like the BMSB, they hitchhiked in cargo from their native lands. As the search for these tiny wasps expands, scientists expect to find them in other locations.
Well, if you are thinking that this tiny wasp could be a problem, you are right on target. It has been shown in the laboratory that Tr. japonicus readily and successfully parasitizes eggs of native beneficial insects, including the spined soldier bug, which is an important predator of both native and invasive pests such as Mexican bean beetle, Colorado potato beetle, cabbage looper, and gypsy moth. So only time will tell if this is the silver bullet, or if the cure is going to be worse than the disease.
The Search is on to find fungi that targets the BMSB and only the BMSB. Fungi that attack insects, called entomopathogenic fungi, can be effective against BMSB. In lab tests, several pure strains (isolates) of a fungi called Beauveria bassiana killed 100% of the BMSB (Gouli et al. 2012). Other effective fungi include Ophiocordyceps nutans and Metarhizium anisopliae (both from Japan), which have been shown to cause nearly 85% mortality of BMSB (Gouli et al. 2012). As promissing as this research is, we are reminded of our past gypsy moth experence. These biological methods require time — time to infect, reproduce, spread, and infect again. Let’s hope that it doesn’t take 80 years this time!
Management For BMSB In Homes
Before Bugs Enter a Building
Mechanical exclusion is the best method to keep stink bugs from entering homes and buildings. Cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the wood fascia and other openings should be sealed with good quality silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced.
Exterior applications of insecticides may offer some minor relief from infestations where the task of completely sealing the exterior is difficult or impossible. A licensed pest control operator should apply applications in the fall just prior to bug congregation. Unfortunately, because insecticides are broken down by sunlight, the residual effect of the material will be greatly decreased and may not kill the insects much beyond several days or a week.
After Stink Bugs Have Entered the Structure
If numerous bugs are entering the living areas of the home, attempt to locate the openings where the insects gain access. Typically, stink bugs will emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. Seal these openings with caulk or other suitable materials to prevent the insects from crawling out. Both live and dead stink bugs can be removed from interior areas with the aid of a vacuum cleaner — be sure to seal the vacuum bag with duct tape when you dispose of it, to prevent any remaining live bugs from escaping.
It is not advisable to use an insecticide inside after the stink bugs have gained access to the wall voids or attic areas. Although insecticidal dust treatments to these voids may kill hundreds of bugs, there is the possibility that carpet beetles will feed on the dead stink bugs and subsequently attack woolens, stored dry goods or other natural products in the home. Although aerosol-type pyrethrum foggers will kill stink bugs that have amassed on ceilings and walls in living areas, it will not prevent more of the insects from emerging shortly after the room is aerated. For this reason use of insecticides is NOT considered a good solution to long-term management of the problem. In addition, spraying insecticides into cracks and crevices will NOT prevent the bugs from emerging and is not a viable or recommended treatment
In sum, the BMSB is an invasive insect unintentionally brought over from Asia; it is a voracious eater that damages fruit, vegetable, ornamental trees and plants and a serious nuisance to homeowners. Broad-spectrum sprays are being used to combat this alien pest, but they also kill beneficial insects that help to control pest populations, presenting a setback for growers and homeowners who use integrated pest management (IPM) to promote nature’s own checks and balances. Biological control of the BMSB from parasites or predators appears to have the potential to provide landscape-scale control of this pest in the future. Natural enemies of stink bugs that are native to North America could potentially play a role in controlling BMSB. In addition, BMSB enemies that are native to Asia could be considered for potential release in the United States, once USDA’s Animal and Plant Health Inspection Service is convinced the imported species will not threaten other insects.
Thanks for stopping by The Garden Shed; we hope to see you again next month.
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