A little better known; a lot more coming
Researchers uncover enough about the stink bug to expect a bumper crop in 2013
This year local produce growers could be hit with an onslaught of brown marmorated stink bugs (BMSB) that rivals the invasion in 2010. That year, the bug caused approximately $37 million in damage to the mid-Atlantic apple crop alone. Many other crops were also hit hard.
Thanks to $5.7 million in funding from the U.S. Department of Agriculture, matched by $7.3 million from other sources, 10 research institutions, including Virginia Tech, formed a consortium last year to launch the “Biology, Ecology and Management of the Brown Marmorated Stink Bug in Specialty Crops” project to study the bug. While lots of data are starting to come in from the project, so far they have raised more questions than answers.
Two entomologists from Virginia Tech working on the project, Chris Bergh and Doug Pfeiffer, along with Jim McNeil, an entomologist from the Smithsonian Conservation Biology Institute (SCBI), were interviewed recently for their take on the status of the bug. They all agree that it’s early days in the research and that it will take a while to collect and interpret enough data on
the stink bug’s biology, behavior and place in our ecology to develop effective ways to control it.
They also agree that, on the basis of the numbers of bugs that showed up at overwintering sites last fall, far more are likely to emerge this spring than did in 2012.
BMSB populations can vary from region and even from site to site on a farm, according to the Tech researchers. While the bug’s numbers are “definitely of concern” here in Rappahannock and north in the mid-Atlantic region, Bergh says, further south in Virginia, growers are not experiencing a big problem with them – yet. But the bug’s “sneaky,” he says. “It builds up . . . under the radar, then all of a sudden, kaboom – it creates issues.”
The role of weather
Last year crops harvested early and in mid-season, including some peach and apple varieties, escaped major damage from the bugs, which apparently got a slow start because of a tropical storm and hurricane in the fall of 2011.
“In hindsight and speculatively, we think that those weather events had a profound impact on the nymphal population of brown marmorated stink bugs, taking a lot of them out of the population,” Bergh recently told growers at a fruit school held by the Virginia Cooperative Extension. McNeil says nymphs, which don’t fly like the adults, are especially vulnerable to wet weather, which can knock them off food sources and potentially expose them to fungi and bacteria on the ground.
Although the bugs had a slow start, their populations rebounded “quite substantially” in August and September, Bergh says. The bug produced two generations here last year, bringing its numbers to essentially the same as in 2010 by the end of the growing season.
Opinions on how cold winter weather affects the bugs differ somewhat among the entomologists, but all interviewed agree that the weather so far this winter is unlikely to have a serious effect on stink bugs overwintering outside. They can withstand temperatures lower than those in a consumer-grade freezer; Tech entomologist Thomas P. Kuhar has said that in tests he’s conducted, the bugs survived temperatures down to -4 degrees Fahrenheit. However, Bergh suggests that the bugs that overwinter in heated manmade structures might be more vulnerable, since they may be drawn out of hibernation for a sustained period of time by the heat, burn off resources and, without food available, starve to death.
Bergh’s team has found light, rather than temperature, seems to trigger spring emergence and the fall search for overwintering spots for the bulk of the bugs. For three years, around Sept. 21, the bugs showed up suddenly en masse on the exteriors of buildings at the Virginia Agricultural Experiment Center in Winchester, seeking a place to overwinter. “There seems to be a very tight window during which these bugs start moving from their feeding sites to overwintering sites,” he said. They have reemerged more slowly in the spring, with the bulk reappearing in May.
How do stink bugs fit into the local ecology?
The brown marmorated stink bug may be putting pressure on our two native stink bug species, which are an important part of our ecosystems and do much less damage to crops. Research at Tech’s Kentland Farm (near Blacksburg) on the Asian bug’s effect on native stink bugs has produced results that are “a little confusing,” Pfeiffer says. While the invader has displaced about 25 percent of the native stink bugs in the upland cane berry crop there, it’s displaced almost 100 percent of the native ones in the vegetable plots in the lower part of the farm, and the researchers are not sure why.
On the positive side, research the consortium project is conducting indicates that some native predators may be adapting to the stink bug and could lower its numbers “somewhat,” says Pfeiffer.
What can growers do?
Careful monitoring of the BMSB and judicious application of recommended pesticides is the best course for growers for now, say the Tech entomologists. “Unfortunately we don’t have a good trap,” which is needed to do effective monitoring, says Pfeiffer. Until recently, a compound developed from a related Asian bug was used as a lure in traps to catch the BMSB. The commercial product RESCUE! Stink Bug Trap, which is available at most hardware stores and co-ops, uses this compound. While the lure has been effective at attracting bugs late in the growing season, another compound specific to BMSB that was recently identified by USDA scientists in Maryland holds more promise for trapping adult bugs earlier.
As Bergh told the growers at the fruit school, a large number of researchers used traps baited with the new lure in 2012 and captured “many more” stink bugs as they emerged from overwintering through mid-season than the other lure did. However, there are other variables in question, including the amount of lure used. Bergh says a lot more research is needed, including the effect of the location of traps in relation to crops and perimeter vegetation that attracts bugs, such as tree of heaven, and the threshold number of bugs trapped that would trigger the use of management tools, such as pesticides.
The Environmental Protection Agency has temporarily allowed wider use of some pesticides to control the bug. However since the available pesticides can harm some beneficial insects, the search continues for a more targeted product. Bergh says a lot of growers are “overall doing a better job” managing the stink bugs, including becoming more familiar with which pesticides are effective and when and how much to apply.
Wine producers faced a potential catastrophe besides fruit damage when hordes of the bug arrived in vineyards in 2010. A taint from the bug was found in the flavor of the raw juice from harvested grapes, so some producers threw out whole crops. However, a local vineyard, Rappahannock Cellars, managed to get ahead of that issue. Tom Kelly, the vineyard manager, said that, with the “heavy infestation” in late August, some of the bugs got mixed into samples picked to determine whether the grapes were ready for harvest and did leave a taint in the raw juice from the sample.
“That immediately sent up red flags, so we put together a treatment strategy immediately,” says Kelly, noting that the vineyard relied on on-site and other testing results that led them to apply an organic-certified insecticide before the picking began. “The grapes we actually harvested for the wine did not have the taint.”
Although Rappahannock Cellars was successful in controlling the stink bug, it still came as a “big relief,” says Kelly, when researcher Joe Fiola at the University of Maryland found that the taint from the bug does not appear to survive the fermentation process. Kelly says he’s found actual damage to the grapes to be “pretty minimal” so far.
As if stink bugs weren’t enough, two more insects will put pressure on farmers this year, particularly fruit growers. The spotted wing drosophila, a vinegar fly from Asia that was first seen in Virginia in 2011, is targeting berries and grapes, among other small fruits.
Three species of native 17year periodical cicadas, which can cause damage to tender tree stems, are also due to emerge en masse this year.
Bergh urges growers to be patient when it comes to BMSB, as researchers are learning more about it every year. To learn more about the bug, go to StopBMSB.org, a website funded under the consortium project to aggregate data on the bug, visit Virginia Tech’s Virginia Agricultural Experiment Station website (vaes.vt.edu), or contact Rappahannock Extension agent Kenner Love at 540-675-3619 or klove@vt.edu.