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An Unprecedented Threat

Brown Marmorated Stink Bugs

by Joy Drohan

Brown marmorated stink bug; photo by Nick Sloff

PHOTO: NICK SLOFF

Shelley Coneybeer sat down on her bed and cried. The past few months of her life felt like a horror movie. Hundreds of stink bugs invaded her home. They crawled on her baby, walked on her in her sleep, and dropped from the ceiling into her hair and her food. “It was like a plague!” she said. “I felt so defeated and helpless.”

Coneybeer’s log home sits on a wooded property in Rostaver Township, about 30 miles south of Pittsburgh. She reports having about 120 brown marmorated stink bugs in her bedroom almost every day during the past winter and spring.

But as infuriating as they can be for homeowners, the impact on agriculture can be staggering. According to the U.S. Apple Association, brown marmorateds caused more than $37 million in apple crop losses in the Mid-Atlantic region in 2010. Much of the crop could not be sold for fresh consumption, which typically brings $20–40 per bushel, but instead had to be sold for juice or cider, which yields only $2–4 per bushel.

The invasive insects from Asia don’t “eat” apple flesh, but they stick their piercing-sucking mouthparts into the fruit and “spit” into the hole. Enzymes in the saliva liquefy the fruit tissue, and the bugs suck it back up. The result is indented depressions and “corking,” soft brown areas under the skin of the fruit. The damage is similar in other crops. In 2010, some growers of peaches and other fruit suffered even more than apple growers because these are sold almost entirely as fresh fruit.

“When our native insects damage 4 or 5 percent of the fruit, we’re talking about disaster,” says Greg Krawczyk, senior research associate in entomology at Penn State’s Fruit Research and Extension Center (FREC) in Biglerville. “But we’ve seen in 2010 that brown marmorateds can damage 70 percent of fruit.” Growers cannot make a living while sustaining injury levels over 10–15 percent.

Fruit growers told Krawczyk in 2010 that if they didn’t get help in managing this insect, they would be out of business in two to three years. Not only do growers face devastating crop losses, but they have to spend more on insecticides as well.

Penn State is one of ten institutions on a new three-year, $5.7 million grant from the U.S. Department of Agriculture’s (USDA) Specialty Crop Research Initiative (SCRI) to reduce brown marmorateds’ effects on tree fruit, small fruit, grapes, vegetables, and ornamentals.

Krawczyk, who is coordinating the Penn State activities within the USDA-SCRI project, says that brown marmorated stink bugs pose a significant national threat to a cross-section of agricultural production.

The overall goal of the grant is to develop nonchemical permanent controls for brown marmorateds before the bugs become a problem in other parts of the country. The team is studying the biology and life phases of this insect, developing effective monitoring and management programs for brown marmorateds, and developing and delivering practical recommendations to help growers and homeowners manage them.

Fifty-one scientists in ten states are collaborating on this project. Penn State alumna Tracy Leskey (’95), research entomologist with the USDA Agricultural Research Service, in Kearneysville, West Virginia, is the grant’s project leader.

“The brown marmorated presents a challenge in that it’s the first stink bug that poses a threat to a wide variety of commodities in the Mid-Atlantic region,” says Leskey.

Greg Krawczyk examines stink bugs in rearing cages used to grow colonies for research and study how they respond to various plant food sources; photo by Steve Williams

Greg Krawczyk examines stink bugs in rearing cages used to grow colonies for research and study how they respond to various plant food sources. PHOTO: STEVE WILLIAMS

 

A Formidable Pest

North America has about 200 native stink bug species, but they don’t tend to aggregate like brown marmorateds do. Good scouting, spot spraying, and natural enemies typically work to control the natives.

Brown marmorateds were first collected in the United States near Allentown, Pennsylvania, in 1996. Growers first noticed serious problems about ten years later, and the trouble intensified in the Mid-Atlantic in both 2009 and 2010.

Several aspects of their biology make them a formidable pest.

They can feed on about 300 different plants. In fruit systems, they prefer stone fruits early in the growing season. In the late growing season, they feast on apples, pears, and berries. The vegetables hardest hit in Pennsylvania are sweet corn, tomatoes, and peppers. Field corn and soybeans are probably important nursery crops where the populations build. The diversity of food means that even if the bugs are controlled in one place, the populations could simply build elsewhere and reinvade all season long.

Each female can lay at least 300 eggs over a lifetime, and the adults are fairly robust, with few natural enemies in the Mid-Atlantic region.

Entomologists believe brown marmorateds produce two generations per year in southern Pennsylvania. The reproductively immature adults typically emerge from overwintering shelters in late April to early June and start eating. They mature and lay eggs, often in late May or early June. The wingless nymphs then feed, grow, and molt to immature adults in late July or early August and start seeking overwintering sites in about the third week of September. In areas where a second generation occurs within one growing season, the nymphs appear in July and August.

Feeding on tree fruits such as apple results in a characteristic distortion referred to as “cat facing,” which renders the fruit unmarketable as a fresh product; photos courtesy of Steve Jacobs

Feeding on tree fruits such as apple results in a characteristic distortion referred to as “cat facing,” which renders the fruit unmarketable as a fresh product; photos courtesy of Steve Jacobs

Feeding on tree fruits such as apple results in a characteristic distortion referred to as “cat facing,” which renders the fruit unmarketable as a fresh product. PHOTOS: STEVE JACOBS

 

Starting from Square One

Despite these insects being easy to see, there’s a lot we don’t know about them. Entomologists have worked on other insect species for about 100 years, but they have only worked on brown marmorateds for about two years. The research team is learning while simultaneously providing farmers with information on how to control them. “It’s very difficult to control something if we don’t understand its biology,” says Krawczyk.

To begin answering some of the basic biology questions about brown marmorateds, Deonna Soergel, a master’s student with Krawczyk, spent hundreds of hours in 2011 in orchards, watching and recording brown marmorateds’ activities. She wants to discern when they’re most likely to feed, move, or fly, and to study the influence of temperature on their activities.

Soergel’s interest in brown marmorateds was sparked during routine insect trap monitoring with her father, Reed, president of Soergel Orchards Family Farm in Wexford, Pennsylvania. Krawczyk was visiting their orchard as part of his extension duties the first time they found brown marmorateds. The Soergels had initially misdiagnosed the injuries as calcium deficiency, as did Tom Haas and some other growers.

 

One Grower’s Story

Tom Haas, of Cherry Hill Orchards in Lancaster, Pennsylvania, grows apples, cherries, peaches, nectarines, plums, apricots, sweet corn, and pumpkins.

For about 40 years now, some growers have been moving away from the use of broad-spectrum insecticides because, besides killing the target insect, they can also kill beneficial insects. A member of the stakeholders’ advisory committee for the SCRI grant, Haas had been using this “integrated pest management” (IPM) for about 10 years. Among other tools, the IPM system uses traps baited with natural, insect-produced chemicals called pheromones that attract others of the same species. Pheromone dispensers placed in orchards can completely disrupt the mating of certain insect species and prevent damage from target insects while greatly reducing the amount of insecticide required. IPM very successfully controlled the main pests on apples in Pennsylvania . . . until 2010.

That year, all of Haas’s crops were damaged by brown marmorateds, with about a 35 percent loss across the board. “I’m in the trees every day, but we were caught completely by surprise,” says Haas. “We sell for the fresh market, so each piece of fruit has to be spectacular.”

With support from the Pennsylvania Apple Marketing Board, the State Horticultural Association of Pennsylvania, and the Pennsylvania Department of Agriculture, in winter 2010–2011 Krawczyk began researching the effectiveness of various insecticides against brown marmorateds. He found that the insecticides Haas was using as part of his IPM program were among the least effective for control of brown marmorateds. Unfortunately, the most effective insecticides against this bug are broad-spectrum products, meaning that they are also very toxic to many natural enemies of tree fruit pests. Therefore, Krawczyk urged growers to practice vigilant and frequent monitoring for brown marmorateds throughout their farms, and to apply effective insecticides only when and where necessary. Using these methods, Haas estimates his 2011 crop losses were only about 10 percent.

With the intensive broad-spectrum-insecticide use this outbreak required, Haas had to nearly abandon IPM practices in 2011. But he hopes to return to IPM practices as quickly as possible.

Leskey’s USDA lab is trying to help. Her team is working to identify a male-produced pheromone that attracts both male and female brown marmorateds to traps. With further work, the pheromone could be used to attract bugs for elimination, reducing the need for insecticides. Late in the 2011 growing season, Leskey’s group identified a pheromone effective for late season attraction of brown marmorateds. All SCRI grant partners, including Penn State, helped test the pheromone for early season effectiveness in 2012.

Tracy Leskey examines peaches at Catoctin Mountain Orchard in Thurmont, Maryland, one of the sites where stink bug fieldwork is being conducted; photo by Jennifer Crandell

Tracy Leskey examines peaches at Catoctin Mountain Orchard in Thurmont, Maryland, one of the sites where stink bug fieldwork is being conducted. PHOTO: JENNIFER CRANDELL

 

Outsmarting the Bugs

Shelby Fleischer, professor of entomology, and John Tooker, assistant professor of entomology, are evaluating trap cropping as a way to protect valuable vegetable crops. Anecdotal evidence suggests that brown marmorateds prefer sunflowers over many other crops and that brown marmorateds occur more often in crops along edges. So Fleischer and Tooker are testing the effectiveness of planting sunflowers near or on the edge of peppers or sweet corn, while Krawczyk is conducting similar experiments in fruit orchards. The hope is to get brown marmorateds to mass in the sunflowers so growers could spray the sunflowers rather than the vegetable crops.

Another way to reduce the use of insecticides in fighting this pest is to augment its natural enemies. Some spiders, praying mantises, and lacewings sometimes feed on brown marmorateds in Pennsylvania, but not enough to control the population.

Fleischer, Tooker, and Dave Biddinger, senior research associate in entomology at FREC in Biglerville, are trying to identify other natural enemies of brown marmorateds that might help reduce populations. They’re focusing first on natural enemies of native stink bug species, says Tooker. “We’re trying to understand if the natural enemies are shifting over to brown marmorateds and if we can bolster their populations to augment control.”

One promising candidate for biological control is a vanishingly small, nonstinging parasitic wasp that lays its eggs in brown marmorated eggs. When the wasp larvae hatch, they feed on and destroy the eggs. In Asia about two-thirds of brown marmorated eggs are parasitized by this wasp. USDA researchers in Delaware are studying this wasp in quarantine to determine whether it attacks only brown marmorated eggs, a prerequisite for release of a nonnative species for biological control.

Another candidate for augmentation is a fly that lays eggs on the adult stink bug. The larvae burrow into and kill the adults. Because these parasitic flies visit some flowering plants for nectar, the team is learning which kinds of flowering plants they prefer and whether they can increase the flies’ effectiveness in killing brown marmorateds by growing more of those plants near crops.

Tooker and Biddinger are also examining the predator populations of various landscapes by placing lab-reared brown marmorated egg masses across southern Pennsylvania to see if anything eats them. This will help determine whether a diverse landscape is less prone to invasion by brown marmorateds and which areas are most at risk from their activity.

Moving from a landscape level down to a plant level, a team of researchers is deciphering brown marmorateds’ mode of attack and plant defenses. Gary Felton, professor and head of the Department of Entomology, wants to know exactly how brown marmorateds cause the injuries that have so badly shaken agriculture in our region. His research group is collecting and analyzing saliva from brown marmorateds to identify the enzymes causing fruit and vegetable discoloration or suppression of plant defenses.

So how does one collect saliva from a stink bug? “My technician, Michelle Peiffer, is adept at it,” Felton says, noting that Peiffer briefly immobilizes a stink bug on ice, and when it revives, it excretes about a nanoliter of saliva.

Kerry Campbell helps develop stink bug colonies at FREC as part 
of an internship and senior project.  Campbell is a biology student at nearby Gettysburg College; photo by Steve Williams

Kerry Campbell helps develop stink bug colonies at FREC as part 
of an internship and senior project.  Campbell is a biology student at nearby Gettysburg College. PHOTO: STEVE WILLIAMS

 

A Plague on Our Homes

Brown marmorateds pose an unprecedented threat to Mid-Atlantic agriculture, but they also torment some homeowners.

Doug Inkley, a scientist with the National Wildlife Federation who serves on the SCRI grant advisory committee, collected 26,000 brown marmorateds from inside his house in Knoxville, Maryland, from January to June 2011. This was after he spent more than $10,000 to replace all of his windows. Inkley kept detailed notes of the count per day taken with his only weapon, a vacuum. He has a scientific research paper on press documenting the infestation.

“The biggest problem with stink bugs for homeowners is emotional stress,” says Steve Jacobs, Penn State urban entomologist. Officially, brown marmorateds don’t destroy homes, although some homeowners with severe infestations have considered moving, and they don’t bite, although there is evidence that they do produce an allergic reaction in some people.

Coneybeer has sprayed with various insecticides, but none has helped for long. Jacobs notes that insecticides won’t kill the bugs within the walls and does not recommend their use to homeowners struggling with brown marmorateds.

“We know that structures are point sources for infestation,” Jacobs says. He is studying where brown marmorateds over-winter and the stimuli that cause them to seek overwintering sites. They seem to prefer the south side of a structure on the north side of an orchard or soybean field. Sunlight bouncing off the building may attract them.

Homeowners harassed by brown marmorateds will rejoice to know that scientists estimate that the overwintering population in 2011–2012 was way down from that seen in 2010–2011. Nobody is sure why, but probable factors are the attempts at control via insecticides and the weather. Hurricane Irene and Tropical Storm Lee brought more than 16 inches of blustery rain to southeastern Pennsylvania in September 2011, which may have knocked bugs off trees and drowned them.


A Ticking Time Bomb?

So should we expect more people to soon face the plague of brown marmorateds? They have been found in more than 35 states, although not all may have reproducing populations, and they may not ever cause significant harm to crops in any of those states. No one really knows, says Krawczyk. “We simply need more time to validate our observations. Each year is different, and biology is heavily influenced by the environment.”

“We are really at the front end of this,” Fleischer says. “In their native range, brown marmorateds are not the top stink bug. We want to push them down to the level of our native stink bugs.”

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Other participants in the SCRI grant at Penn State include Jayson Harper, professor of agricultural economics who is calculating costs growers will incur to manage brown marmorateds through the strategies developed in this project, and Michael Saunders, professor of entomology who is working on repellents and attract-and-kill strategies for brown marmorateds in commercial crops.

Distribution of BMSB in the United States

Distribution of BMSB in the United States. PHOTO: USDA