A couple of years into research on how to thwart invading brown marmorated stink bugs (BMSB), solutions remain elusive. However, research on the problem, including a study done here in Rappahannock County this summer, is yielding useful information.
Native to East Asia, the BMSB was accidentally introduced into Pennsylvania in the late 1990s. First reported in Virginia in 2008, by 2011 the bug had spread to 60 percent of the continental United States. Researchers have found it can survive for extended periods of time at low and high temperatures and is highly mobile, migrating between hosts and hitchhiking on a wide array of materials, according to a 2010 U.S. Department of Agriculture report.
While some county residents have reported being “bitten” by the bugs, researchers say that the bugs do not bite, nor do they breed while overwintering indoors. They do, however, exude a pungent odor when threatened, which, along with their sheer numbers, makes them unwelcome guests inside.
As the bugs started massing on houses again this fall, Rappahannock residents fought them with bug-sucking guns, jars filled with water and soap, fly swatters, vacuums and insecticides – all with limited results. Most experts say the best strategy is to keep them out of structures in the first place by sealing cracks and other openings and using window-grade screen, even on attic vents.
For farmers, the Halyomorpha halys is more than a smelly nuisance. The U.S. Apple Association reports that mid-Atlantic apple growers lost $37 million in 2010 from stink bug-related damage. In areas with heavy concentrations of stink bugs, 50 to 100 percent of apple crops were lost. One official of the association was quoted by PBS’ Newshour as saying that the bug was the biggest threat posed to apple growers by a single insect in the 40 years that he’s been in the industry.
On its Northeastern IPM Center website, the USDA reports that the value of crops that are susceptible to damage by the BMSB in the 33 states in which it’s been spotted exceeds $21 billion. In response, the department has awarded $5.7 million to 10 institutions across the country to do research on the bug and helped fund websites that aggregate research results, such as StopBMSB.org.
When the BMSB first emerges from hibernation in the spring, it heads to trees to feed and lay its eggs, then moves on to crops that are near them and continues to reproduce throughout the summer. It goes through five nymph (larval) stages before becoming an adult.
Since the invasion started, the mid-Atlantic region has had the “highest densities of bugs and concomitant crop damage,” says Virginia Tech vegetable entomologist Tom Kuhar in an online slide presentation on the impact of the bug on tomato crops. He says entire crops of tomatoes have been ruined on some Virginia farms.
BMSB is a moving target in many ways, with reports varying on their numbers, even within a small area. While an Oct. 8 Washington Post article with USDA entomologist Tracy Leskey reports a 60 percent increase in populations in Frederick County, Md. over last year, the University of Maryland, on its Home and Garden website, says that “populations have been significantly lower in 2012” in the state overall.
Here in Rappahannock, Cooperative Extension agent Kenner Love said he hadn’t seen as many of the bugs in the county this summer as last and wasn’t sure why. However, he did say that the bug presented a new challenge when it first arrived and the Extension and farmers have learned more about how to target pesticide application for them, which has likely helped keep populations down this summer.
The UM website cites weather as another possible reason for a decline in BMSB populations this year: late summer rains last year destroyed nymphs, followed by a warm winter in which, on warm days, the adult stink bugs came out of their overwintering sites, “using up valuable body food reserves causing a fair amount of mortality.”
While the BMSB will feed on a wide range of hosts, researchers have found it does show distinct preferences. Not surprisingly, reports Kuhar, it is found in “extremely high numbers” on three trees that are also from Asia: paulownia, tree of heaven and mimosa. However, it’s also found in “pretty high numbers” in native eastern redbud, mulberry, black walnut, catalpa, wild cherry and silver maple. Among cash crops, research results on preferences vary, but apple, cherry, citrus, ﬁgs, mulberry, peach, pear, persimmon, grapes and soybeans generally top the list.
Most local farmers report seeing fewer BMSBs and less damage to crops this year until early fall, when swarms of the bugs were seen flying into crop areas from the woods. While the bugs were likely on their way to find shelter for the winter, they did some damage along the way.
At Roy’s Orchard in Sperryville, owner Roy Alther says that, while the apples that he picked earlier escaped damage for the most part, his pumpkin crop was hit hard by this late wave of the bugs. Sean McDermott, farm manager of Washington’s organic-certified Farm at Sunnyside, which is owned by Nick and Gardiner Lapham, reports “significant” damage this year to tomatoes, peppers, eggplants and corn, particularly late in the season. Asian pears also took a big hit in September, so all of that crop was pulled early, he says.
Louis Moore, Jr., whose family has owned Moore’s Orchard in Flint Hill for generations, said the BMSB didn’t affect his apple crop. The Moores use integrated pest management, which includes carefully targeted pesticide application, which he says “definitely helped.” Damage to their peach crop was also limited, with peaches closest to the woods being hit harder, he says.
While stink-bug numbers may have been down this summer, Moore and his sister, Dorothy, say they’re seeing more this fall than last. Dorothy says her tomato crop, to which she doesn’t apply pesticides, was “fabulous” until early September, when she was suddenly finding 10 or 12 bugs in various stages of development on each tomato, with corresponding damage to the fruit.
Rachel Bynum of Sperryville’s Waterpenny Farm, which uses “ecologically based sustainable farming methods,” says that last year’s peppers took a heavy hit from the bugs, but this year they “haven’t noticed a particular impact” except on a few varieties of cherry tomatoes.
Taliaferro Trope, a budding entomologist and daughter of Rappahannock native Stuart Fletcher, did a study of the bug’s feeding preferences at Sunnyside during June and July. In discussing her findings in a recent interview, Trope says she, like other researchers, found the bugs are “extremely opportunistic” and “will take advantage of any available food source,” but do have preferences.
At Sunnyside, Trope says, the BMSBs preferred ailanthus to peach and mulberry, apple to ailanthus, pear to apple and cherry to pear. She also found “large populations of BMSBs” in corn, blackberries and mulberries when they were fruiting, which “were seen to be a favorite overall” during the study period. When smooth sumac fruited in late July, she says, the bugs moved there. However, she also says that while ailanthus trees may indeed lure the bug away from cash crops and therefore “seem beneficial,” she recommends that the tree not be planted. “The hope is to eradicate both the BMSB populations as well as the ailanthus, since they are both invasive,” she said.
On the basis of these preferences, Trope suggested planting sumac and mulberry trees around the perimeter of cash crops to lure the BMSBs away from the latter while “creating more habitat space for beneficial insects to reside.” Bynum also noted this trapping effect, saying the cherry tomatoes that were damaged at Waterpenny may have concentrated the bugs in one area, saving other crops. She also attributes their low crop damage to spreading the risk through crop diversity – “many varieties and many plantings.”
Right now, insecticides seem to be the most effective way to battle the bug for growers who are willing to use them. In his research, Kuhar found that many different types of broad-spectrum insecticides (including organic pyrethroids and neonicotinoids) have proven to be effective against the BMSB but also adversely affect beneficial insects, such as bees and insects that prey on other pests. In using pesticides to kill off the stink bugs, produce growers could end up with infestations of aphids and other pests, he says, and therefore management strategies that use these pesticides “are not sustainable.”
Among other management strategies that have proven helpful are spraying water in combination with application of pesticides. McDermott says that the few certified organic insecticides are expensive and produce limited results, but Sunnyside does spray kaolin clay. Some farmers are using large black lights to trap thousands of bugs at a time.
What may prove to be the most effective and ecologically sustainable way to manage the BMSB – the Trissolcus genus of predatory wasps – is being researched at Rutgers University and at USDA. Having co-evolved with the BMSB in East Asia, these wasps parasitize up to 70 percent of the bug’s eggs in China.
So far Trissolcus wasps have also been observed as parasitizing only the eggs of the BMSB and therefore should not be a threat to our native species. However, researchers are keeping the wasps in quarantine and plan to monitor them through many more generations, which could take years, to ensure the wasps would pose no hazard to native species if released.
Some researchers are looking to possible native predators as a solution. The UM Home and Garden website says that, while a study in 2005 found less than 5 percent of BMSB eggs were parasitized by native species, UM researchers are now reporting seeing that rise to 12 to 29 percent. Bynum and others have reported anecdotally seeing local native predators – including bees, spiders, mantises and birds – chowing down on the adult bugs.
One thing that everyone seems to agree on is that more research on the BMSB is needed. Virginia Tech’s entomology department offered Trope a full scholarship to pursue post-graduate work in entomology at the school and, she says. At the department’s urging, she is considering continuing her research on the BMSB at Sunnyside.