Here’s what you should know about one of this year’s major soybean pests
DES MOINES, Iowa and WASHINGTON – The emerald ash borer may be a significant tree pest, but what about an agricultural nuisance that gets into your home?
The brown marmorated stink bug is classified as a true bug, due to its piercing mouth parts (called a stylet) which penetrate plant tissue to feed. That feature is also why it is a major agricultural pest.
“In corn and soybeans in Iowa,” explains State Entomologist Robin Pruisner, “it’s going to be a grain and seed quality issue, because it likes to feed right through the husk or pod and feed directly on that seed. It causes a reduction in seed quality as well as grain quality.”
The bug injects plant tissue with digestive enzymes, which can result in a necrotic spot or even reduced germination, if the stylet reaches a seed. Controlling the brown marmorated stink bug is a challenge, because it pierces plant tissue to feed. In so doing it bypasses insecticide coatings on the outsides of plants.
Native to eastern Asia, the brown marmorated stink bug first appeared in Allentown, Pennsylvania in September of 1998. It’s believed that the bug first landed on U.S. shores in 1996, but since that time, it’s made its way into 40 states: every state east of the Mississippi River, along with Iowa, California, Washington state, and even Ontario. It first appeared in Iowa in Scott County in 2012. Since then it’s been found in 11 Iowa counties: Muscatine, Des Moines, Dubuque, Linn, Johnson, Black Hawk, Story, Polk, Warren, and Pottawattamie. But Muscatine County and Pottawattamie County are on opposite sides of the state; how did the brown marmorated stink bug get all the way to the Nebraska state line? The same way the emerald ash borer has been traversing the state.
“They’re hitchhikers,” says Pruisner, adding that the brown marmorated stink bug is less picky than its green counterpart. “It is very famous for getting into a box in your car, and just going and riding along with you. So, it’s moved by humans. We’ve had reports of people who are buying things off the Internet from the East Coast, and when they get the box in the mail, it’s also full of brown marmorated stink bugs.”
Winter temperatures from December through February averaged 14.6 degrees Fahrenheit across most of the state. That was enough to stunt the population of some early-season bean-leaf beetles, but probably not the brown marmorated stink bug. Pruisner contacted colleagues in Maryland, who said even this year’s polar vortex did little to keep populations in check.”
“They typically see a 50% death loss in any given winter,” says Pruisner, “and [my colleagues] said they’re right on track. So the brown marmorated [stink bug] has a habit of trying to get into man-made dwellings. And so, whether it’s super cold outside or not quite so cold, if they’re in your attic or garage, they’re not as affected as much by the cold weather.”
USDA Entomologist Tracy Leskey says one problem is that brown marmorated stink bugs come from eastern Asia, where plummeting temperatures aren’t unusual. In addition, Leskey says the bug usual enters winter with enormous populations, which means there’s no shortage of surviving insects to multiply in the spring.
Currently Leskey is conducting research in South Korea. One goal is to determine the brown marmorated stink bug’s natural predators, and the appropriateness of introducing them in the United States. Tiny parastic wasps called Trissolcus, are known to attack the eggs of the brown marmorated stink bug, while a naturally-occuring fungus, called Ophiocordyceps nutans, has been observed attacking the bug in Japan, much like the related “zombie ant” fungus.
The decision to introduce wasps or fungi deliberately in the United States rests with USDA’s Animal and Plant Health Inspection Service.
Leskey’s second goal in Korea is a continuation of ongoing U-S-D-A research into the bug’s own pheromones.
“What we are doing is setting up pheromone traps to establish that the brown marmorated stink bug in its native range responds to the pheromone that we recently identified in the United States,” says Leskey. “By doing this project, we can then evalute its reponse in its native range, and if they are attracted similarly, we can then state that, for worldwide detection purposes, this stimulus should work. In other words, if you’re trying to determine if the brown marmorated stink bug is showing up anywhere else, the use of these pheromone traps should be reliable.”
Pioneer Hi-Bred suggests soybeans should be scouted for the brown marmorated stink bug from the R2 stage (full bloom, before pod development) until mid-August, pointing out that populations are highest at dusk and dawn.
The brown marmorated stink bug poses a risk to U.S. crops valued at almost $21 billion.