By Vicky Boyd
Growers and even homeowners in the Northeast and Mid-Atlantic states are under siege from a smelly foreign invader that has a wide host range, can render crops unmarketable for fresh uses, has few native enemies and is extremely mobile.
To top it off, only a handful of broad-spectrum pesticides are known to control the brown marmorated stink bug. Because the insecticides are non-selective, they also kill beneficial insects, upsetting biological control.
“I grew up on a farm in the Midwest, and we had stink bugs. But the level of destruction [from this pest] on field crops was absolutely stunning,” says Mark Seetin, director of industry policy and regulatory affairs for the Vienna, Va.-based U.S. Apple Association. “It’s of grave concern. I can’t rate it any higher in terms of a potential threat for the reasons that it’s voracious, it feeds in all five instars, it likes apples and very few pesticides have been found to work on it at this stage.”
In response to the pest, scientists within the U.S. Department of Agriculture and several universities formed a working group last summer to set research priorities and begin conducting trials.
USApple, at the prompting of Maryland apple grower Robert Black, convened a meeting in late October to bring lawmakers, researchers and association members up to speed on the pest.
Few pesticide choices
One of the challenges is few registered pesticides will control the marmorated stink bug. Select pyrethroids and Lannate appear to kill it, says Galen Dively, an emeritus professor of entomology at the University of Maryland in College Park. But they are contact products and provide short residual control.
Brown marmorated stink bugs are highly mobile. Shortly after a grower treats a field or orchard, new stink bugs move in from the outside, returning populations to where they were before treatment.
The insecticides also are broad spectrum and kill beneficial insects, which are part of an integrated pest management program.
For Black, who owns Catoctin Mountain Orchard in Thurmont, Md., weighing stink bug control against an integrated pest management program that he spent more than a decade building was a tough decision.
“We spent the last 12 to 15 years doing IPM and have a huge predator population,” he says. “Here we are building our predator populations up, and we’ll wipe it out in a year. I hadn’t used pyrethroids for years, but I did on my later varieties in hopes of salvaging them.”
Researchers seek answers this winter
Researchers hope to answer a few of the pesticide questions this winter. They will begin to screen both registered and unregistered pesticides as possible short-term control to help growers survive another season, says Greg Krawczyk, an Extension fruit entomologist at Penn State University who’s involved in the pesticide screening.
The screening will involve rearing marmorated stink bug colonies in the laboratory, then subjecting them to different compounds to determine residual activity.
“We know how to kill them—that’s not the problem,” says Krawczyk, who’s based at Penn State’s Biglerville Fruit Research and Extension Center. “When the insect contacts the spray, it will die. That’s the way we do it at the moment. We don’t know if the [pesticide] residual doesn’t affect them or there’s such a huge influx that they’re able to overwhelm the residual.”
In the end, he says, more sustainable, longer-term solutions will be needed.
“It’s not sustainable for growers to go and spray every seven days to eliminate newcomers to the orchard, Krawczyk says. “Our short-term goal is to give growers something they’ll be able to do. We have to help growers now so there will still be growers a few years from now.”
Longer-term goals include developing treatment thresholds and learning more about stink bug behavior, alternate hosts, biological control and pheromone-based mating disruption, says Tracy Leskey, a research entomologist at the Agricultural Research Service’s Appalachian Fruit Research Station in Kearneysville, W.Va.
Best trapping methods
Last season researchers also looked at the best traps to monitor marmorated stink bug populations in fields and orchards. Black says he offered up his orchard so he could gain first-hand knowledge of pest populations, stink bug movement and fruit damage.
In the wild, marmorated stink bugs emit a chemical that attracts tens if not hundreds of other stink bugs to an area.
ARS researchers in Beltsville, Md., have identified that chemical, known as an aggregation pheromone, Leskey says. The chemical isn’t quite ready for field testing, although she hopes it will be by next season.
During the 2010 season, Leskey tested a black pyramid trap modified specifically for stink bugs in six commercial fruit orchards. It contained a generic stink bug lure that’s commercially available. At the peak, one trap caught about 1,500 stink bugs during a one-week period.
Unfortunately, she says, the trap catches didn’t correlate to damage levels within the orchard.
“We’ve learned so much this summer, but there’s so much to learn still,” she says.
Get to know the brown marmorated stink bug
The brown marmorated stink bug, a native of China and east Asia, is the size of a green stink bug—about 0.6 inches long. Known scientifically as Halyomorpha halys, the brown marmorated stinkbug has the typical shield shape of other stink bugs. Adults are brownish with characteristic white or off-white antennae segments and darker bands on the membranous, overlapping part at the rear of the wings. They have red eyes.
The early instars, or life stages, are mostly reddish yellow and grow to more resemble adults as they reach the latter instars.
And as its name implies, the brown marmorated stink bug emits a foul-smelling chemical when squeezed or squished. Some have compared the odor to strong cilantro, stale gym socks or skunk.
Since the pest was first confirmed in Allentown, Pa., in 2001, it has been found in 23 other states coast to coast.
Growers in the East reported spotty damage in 2009. During the 2010 season, growers and homeowners in the Northeast and Mid-
Atlantic reported widespread damage. A few apple and peach growers reported fruit injury of 80 percent or greater.
“This is the worst pest I’ve seen in over 40 years, including grad school,” says Galen Dively, an emeritus entomology professor at the University of Maryland in College Park. “There are just so many hosts. We don’t know a lot about it because it’s an invasive species, so we’re kind of operating blindly.”
Ever-increasing host range
The host range is extensive and growing.
Among the hosts documented so far are apples, stone fruit, grapes, tomatoes, peppers, egg plants, cucurbits, corn (both field and sweet), green beans and soybeans. It also favors ornamental plants and trees, including roses, honeysuckle, Paulonia, Norway maple, catalpa and crabapple.
This new stink bug appears to have two generations per year in the Mid-Atlantic states, says Tracy Leskey, a research entomologist at the Agricultural Research Service’s Appalachian Fruit Research Station in Kearneysville, W.Va.
In China, researchers report up to five generations annually.
It frequently migrates from wooded areas into agricultural fields, with heavier populations initially seen along field or orchard edges.
“The green stink bug barely overwinters in our area,” Dively says. “Usually you see this [green] stink bug late in the season because it takes a while to build up.
“But this insect [the brown marmorated stink bug] is right out there in the spring because it has no problem overwintering.”
An aggressive feeder
The brown marmorated insect has a long stylette, or feeding tube, that it inserts into the plant and sucks out the plant juices. The stylette is so strong that it can pierce a tough corn husk to get to the tender kernels underneath, Dively says.
“I couldn’t believe that it could actually get through the husk,” Dively says.
As it feeds, the stink bug injects saliva that contains a plant enzyme and a plant toxin.
In apples, the toxin turns the plant tissue surrounding the feeding area into a corky mass, rendering them unsuitable for the premium fresh market.
In tomatoes and peppers, this stink bug also injects yeast organisms that lead to eventual fruit rot.
Dively says the saliva or toxin also affects the plants, causing the fruit to be misshapen.
The brown marmorated stink bug has five immature life stages, or instars, and all of those—as well as adults—are capable of damaging fruit and plants.
Few natural enemies
Most stink bugs lay eggs that resemble small barrels close together. Brown marmorated stink bug eggs resemble pearls.
In the United States, small, parasitic wasps lay their eggs in native stink bug eggs and provide biological control. Since the marmorated stink bug is a foreign invader, Dively says no one knows whether there are native beneficial insects that will parasitize the eggs.
In China, where the pest is native, researchers report up to 50 percent egg parasitism from a small wasp.
In the United States, a small tachnid fly will lay its eggs in the bodies of native stink bugs, Dively says. The immature feed internally and emerge from the stink bug body as an adult, killing the stink bug in the process.
But the native tachnid flies don’t seem to survive in brown marmorated stink bugs, he says.