Defense strategies

Brown marmorated stinkbug nymphs develop through five instars, all feeding on fruit. Nymphs and adults cause both external and internal injury.

Photo by Tracy Leskey

One of the easier ways of monitoring the brown marmorated stinkbug’s invasion status is by listening to homeowner complaints, says Dr. Tracy Leskey, the U.S. Department of Agriculture’s team leader coordinating efforts to control the bug. Wherever they are, the bugs seek winter shelter in buildings, aggregating in large numbers, covering whole walls before finding their way into walls and attics, often hiding under insulation. People notice—and complain—when they encounter this bug in numbers.

Dr. Aijun Zhang, a research chemist at USDA in Beltsville, Maryland, is studying the chemistry behind this grouping behavior. Leskey, who has worked extensively with attract-and-kill strategies with plum curculio, hopes this has potential.

Zhang said that the insect’s grouping behavior might not be pheromone-based. However, he has found one pheromone emitted by young male adults that might have potential as a trap lure during mating season—which would be a very useful time to attack the insect. His work is in its early stages.

A key problem with pesticide programs is not that pesticides won’t kill the bug, but there is such a vast pool of mobile bugs that reinfest soon after spraying. A major gap in spray programs will be during the preharvest interval.

Basic biology

Much of what we know about the brown marmorated stinkbug we owe to Dr. George Hamilton, a research entomologist at Rutgers University in New Jersey, and his graduate student Dr. Anne Nielsen, who made this insect’s basic biology her research project for her doctorate. She’s now at Michigan State University—expecting the bug will follow her there.

The USDA’s Animal and Plant Health Inspection ­Service (APHIS), in a report in October, classified the six Mid-Atlantic states as having established populations of brown marmorated stinkbugs causing agricultural damage, ten states as having established populations but not experiencing crop injury (California, Connecticut, ­Indiana, Kentucky, New ­Hampshire, North Carolina, New York, Ohio, Oregon, and Tennessee), and another 11 states having detected the insect but not knowing whether ­populations are ­established. APHIS rates the future ­agricultural damage potential from this insect as high.

Oregon

Oregon State University entomologist Dr. Peter Shearer was at Rutgers University before coming to Hood River, Oregon, in 2004, and he met the brown ­marmorated stinkbug while in New Jersey.

He was on Nielsen’s committee when she and Hamilton were doing the first studies on the basic biology of this new invasive bug. Shearer and Hamilton published a paper in 2002 entitled: “Brown marmorated stinkbug—a new exotic insect in New Jersey.”

The bug is not yet listed in Oregon as an agricultural pest, but it is established there on the fringe of tree fruit and wine grape country, Shearer said.

“The value of specialty crops here is huge,” he said. “This bug is threatening a multibillion-dollar industry.”

Not only is he concerned about what could happen in wine grapes, he said Oregon is a leading producer of hazelnuts (filberts). “We were evaluating filbert selections when I was at Rutgers,” he said. “This stinkbug really nailed them.”

As well as being a threat to fruit, the bug feeds on ­tender foliage, especially if it’s sweet. Maple trees in woodlots appear to serve as a host to the bug, which greatly enhances the reservoir of bugs waiting to invade growers’ crops.

Heading south

Dr. Chris Bergh, an entomologist at Virginia Tech, sees himself on the leading edge of the bug heading south into warmer climes, where it may develop more generations and do it faster than it has in the Mid-Atlantic area. There, it usually has one generation a year, but the adults ­continue to lay eggs, so there is a mixture of nymphs of different instars along with adult bugs.

In an analysis made by APHIS in October, it noted that the bug is a highly mobile pest and is considered a migratory insect that easily moves between hosts, migrating from plants with early-ripening fruit to those with late-ripening fruit. Nymphs and adults, like other stinkbugs, are capable of dispersing to feed on susceptible hosts. If disturbed, both nymphs and adults drop off host plants or escape to sheltered areas. Adults are also capable of long-distance flight.

Currently, there do not appear to be any environmental limiting factors for the bug’s populations, APHIS reports. In the Mid-Atlantic states, there have been no signs that populations are on the decline. Between 2004 and 2008, the population in Beltsville, Maryland, rose from undetectable to abundant and appears to be rapidly expanding.

The abundance of hosts creates, Bergh said, the potential for a sustained invasion ongoing through the season. While pesticides will knock down or kill them, there appears to be little activity beyond the direct contact.

The insects walk on tiptoes, making little direct ­contract with surfaces and inserting their sucking mouthparts into the fruit, keeping away from pesticide residues.

Bergh is hoping to have some solid recommendations for his growers this year. “Growers here are very ­concerned,” he said.