N.C. scientists race to find something to control a new pest that decimates crops, trees
By Alicia W. Roberts
awroberts@charlotteobserver.com
The Asian stink bug has started its migration into North Carolina, and a team of researchers at N.C. State University have prepped their labs, set their traps and launched a monitoring website – all in an effort to stop the pest’s spread.
Their work is urgent. This insect, also known as the brown marmorated stink bug, has decimated crops in the mid-Atlantic states. The North Carolina researchers have their eyes on apples, peaches, tomatoes and corn – aiming to save these high-dollar crops from the stink-bug scourge.
“It’s where a small amount of damage has a pretty big economic impact,” said Jim Walgenbach, a researcher at N.C. State’s Mountain Horticultural Crops Research & Extension Center, in Mills River.
Farmers in northern Virginia, eastern West Virginia, Maryland, Delaware, and south central Pennsylvania reported losing more than half of some crops in 2010 – mainly apples, peaches, blackberries, raspberries, strawberries, tomatoes, peppers, sweet corn and soybeans. Some reported total crop loss.
Asian stink bugs also love ornamental plants, so home landscapes are at risk, too.
“It really wasn’t until last year until the populations (in the mid-Atlantic states) unexpectedly exploded,” Walgenbach said. “Listening to my colleagues up there, it sounded like a biblical plague.”
North Carolina’s turn
Walgenbach and partner Mark Abney, who is based at N.C. State in Raleigh, think this could be the season the Asian stink bug population explodes in North Carolina.
In early July, Walgenbach captured Asian stink bugs in residential areas in trees and shrubs – tree of heaven, catalpa and wild cherry – and a few in trees near farm fields.
“This distribution pattern is consistent with the early stages of infestation by an invasive insect,” he said. It’s difficult to predict how quickly populations will increase and become widespread, “but populations are likely to expand more quickly here than farther north, because of our warmer climate.”
He expected to find many more Asian stink bugs beginning in August.
“We’re at the boundary of its expansion. It’s moving southward,” Abney said from Raleigh.
“My grad student has found them right outside the office, in the trees.”
Late last year, Walgenbach started getting reports of some damage to peach and apple orchards in Western North Carolina. Toward October and November, he began hearing about masses of Asian stink bugs crawling in and near homes and other structures in the mountains and the Piedmont.
Walgenbach even found a few in his home.
Adult Asian stink bugs like to spend the winter in structures, where they can be a nuisance but generally don’t cause any damage. If you grab one, it secretes a chemical that releases a strong odor. Walgenbach said the smell doesn’t bother him; his lab technician says the stink bugs have a strong almond-like scent when crushed.
Farmers and gardeners should report any sightings to their local extension office or at N.C. State’s new online monitoring site.
‘Pockets of high populations’
The Asian stink bug, native to China, first showed up in the U.S. in 1998, in Allentown, Pa. The insects have spread slowly, and Walgenbach said they’ve probably lived in North Carolina for a few years in small, isolated populations.
But their potential for growth in the Tarheel State could spook any farmer or proud home gardener.
“(This year), I expect to see pockets of high populations in a few areas,” Walgenbach said. “In some apple orchards, I suspect the populations will be fairly large … peaking in September and October.”
North Carolina has the perfect conditions for Asian stink bugs:
The state’s warm climate will allow the insects to reproduce as many as four or five times each season, increasing the number of crop devourers with each generation.
All of the plants the stink bug loves to eat grow in plentitude here – in farms, gardens and the wild.
The insect has no natural enemies in the United States. American parasites that prey on native stink bugs won’t adapt to the Asian stink bugs for years – if they ever do.
Scientists also have yet to identify a targeted insecticide that works on the Asian stink bug. Broad-spectrum insecticides would kill the Asian stink bug – but would terminate all the beneficial insects in the area, too.
And turning to broad-spectrum insecticides would disrupt decades of pest-management research, Abney said.
“You don’t want to kill all insects in an area,” he said. “Many are beneficial, and some that are pests (are) in low enough populations that they’re not a problem.
“Plus, you run the risk of developing resistance, so you might get some populations that explode because you kill off their predators or enemies – aphids and whiteflies, for instance.”
They’re hard to kill, too
Besides that, the Asian stink bug seems to show incredible resilience, as farmers in the mid-Atlantic states have seen.
“There are so many stink bugs out there in places where there are high populations, they can treat the bugs that are present, and it will kill them, but then more bugs move in,” Abney said. “And the residues don’t kill the bugs that come later.”
At this point, farmers in N.C. have no defense.
So Walgenbach and Abney are monitoring and trapping Asian stink bugs in the field, hoping to devise a plan for crop rotations that might hinder the insect’s spread. And they are breeding stink bugs in the lab, with plans to test an array of chemical sprays against the pest.
The hope is that, by the time the stink bug population spreads across North Carolina, we’ll know how to manage the insects – and mitigate the damage they can do.
“Agriculture is still our No. 1 industry, and the diversity of agriculture in North Carolina is pretty astonishing,” Abney said. “It’s a lot more diverse than to the north. The potential hosts (for the Asian stink bug) are plentiful.
