At last, the “Vine that Ate the South” may have met its match.
To most longtime Southerners, it sounds great: a bug that loves to eat kudzu and can kill off half an infestation of the tangled vine in a couple of years.
What’s not to like?
A lot, it turns out.
The bean plastapid, commonly called the kudzu bug, also likes to eat soybeans as well as wisteria and some ornamental plants. (Kudzu, wisteria and kudzu bugs all come from Asia, especially Japan.) Like stink bugs, kudzu bugs smell bad, and like ladybugs, they try to come inside people’s houses. They fly in clouds and form clumps of thousands on white homes. The insect leaves behind orange stains when smashed and gives some people a skin rash.
In a debate about which is the bigger pest, kudzu might actually lose.
Georgia is the first state the bugs invaded from Japan, and since 2009 they have spread with breathtaking speed.
Tracie Jenkins, an assistant University of Georgia professor of applied insect genetics who lives in Macon, said the earliest ones were found in 2008. In 2009, they had become a pest to homeowners in eight or nine suburban counties around Atlanta, where they apparently spread from Hartsfield-Jackson Atlanta International Airport.
“Homeowners were going nuts around Atlanta,” Jenkins said. “Tens of thousands of these stinky little bugs were attaching themselves to the sides of people’s houses.” The bugs are attracted to light-colored paint on cars and houses and to tall things and people as they mate and seek crannies in which to overwinter.
Every female kudzu bug can lay 250 eggs a season, and there can be so many bugs in one infestation that a single sweep of a 15-inch-wide butterfly net gathers hundreds, Jenkins said.
Now they are found throughout Georgia and South Carolina and in six other states, as well as Central America.
The question is how to slow the spread or reduce their destructive power.
First, UGA scientists pooled their knowledge and requested help from Asian colleagues to identify the bug. Then they continued their detective work.
Jenkins examined the bugs’ DNA and found that they all descended from a single female line. Then she sequenced the bug’s entire genome.
The detective work can be more fun than the field work in this case. Jenkins gathered hundreds of kudzu bugs from a foreclosed house overrun with kudzu in an upscale north Bibb County neighborhood. Driving them home, bagged in freezer bags, left her car reeking. She stored them on ice in a cooler that she subsequently had to throw out.
Now she’s using DNA from more than 300 bugs collected in eight states, looking for genes that offer the bug resistance to insecticides, which could be targeted for changes that would weaken the insect.
Jenkins wants to examine the genetic diversity of the bugs -- variations in their genetic building blocks -- using DNA from not only the Southeast but also from kudzu bugs from China, India, South Korea and even Honduras. Bugs apparently came from those countries to Atlanta by plane.
Aside from changing the genetic code of the bug itself, Jenkins has identified another option. She and colleagues at other universities are working on three different kinds of bacteria that live within the bug, apparently helping it digest its food and perhaps perform other functions.
“So you have this machine with six legs and an exoskeleton, and inside you have gears made up of three bacteria,” Jenkins said. Without at least some of these bacteria, the bugs would probably die, so tinkering with the gears might make the machine break down, Jenkins said.
While she pursues genetic solutions to the kudzu bug invasion, other entomologists investigate the possibility of importing another insect to prey on the kudzu bug. On its home turf, the insect is kept in check with the help of a wasp that lays its eggs in the eggs of the kudzu bug. These wasps are being tested to see if releasing them here would harm only the kudzu bug -- or some native insects as well. Jenkins said some native wasps also have laid their eggs inside kudzu bug eggs.
“Nature has a way of righting itself,” she said.
Dining on soybeans
At first, it might seem that the kudzu bug itself is an example of nature correcting the kudzu problem. The insect has sucking mouth parts that it inserts into the stem.
Jim Hanula, an entomologist with the U.S. Forest Service in Athens, has found the bugs are able to reduce the size of a kudzu patch by half within two years.
“They are not going to completely eliminate kudzu,” he said, but scientists want to study the long-term effect of the bugs on the vine’s resilience. Kudzu relies on its root system when its leaves die back each winter. If bugs aggressively feed on it year after year, that could reduce the energy reserves in the plant’s roots, allowing trees to grow through the vines, Hanula said.
Unfortunately, kudzu bugs cause the same kind of stress to soybeans, diverting the plant’s energy from bean production and reducing yield. According to the state Cooperative Extension Service, about 180,000 acres of soybeans, with a value of more than $168 million, are planted in Georgia a year. And soybean prices have been higher than usual lately.
UGA entomology professor Phillip Roberts said scientists in Tifton have conducted 24 field trials over the past three years, concluding that the kudzu bug causes a 20 percent loss in soybean yield if farmers don’t spray infested areas. He said research from the most recent growing season suggests that soybeans planted earlier will be less susceptible to kudzu bugs.
He said he hopes next year to figure out more about the “sweet spot,” when the bugs are done moving and a single spray could eliminate them from a field for the year. Roberts said a $10-per-acre insecticide treatment at the right moment in a few fields around Tifton saved 20 bushels an acre -- about $300 worth of yield.
What Roberts learns could be important not only for Georgia farmers but also for Midwestern farmers, whose soybean crops are much larger.
The kudzu bug is expanding its range rapidly and likely will move anywhere kudzu lives, Jenkins said. The ease of international travel, combined with global warming, probably will expand the range of invasive species like the kudzu bug that rely on a temperate climate. Georgia’s own springs are coming a month sooner, and summers are ending a month later than in the past, she noted.
In Dodge County, where about 3,500 acres were planted in soybean, growers were fortunate that the bugs became most active after beans had already set, county extension agent Greg Slaughter said.
In Taylor and Peach counties, farmers were not so lucky.
“It’s amazing how quickly they have adapted and overrun us,” said Jeff Cook, the county agent for both. He said almost all his farmers sprayed for kudzu bugs, which became prevalent when the plants were still seedlings.
In fields near kudzu, he said, “you could drive by the field and smell them. You could easily find 10 to 20 on a plant.” The kudzu patches themselves looked as if they’d been hit by frost in the summer.
Cook said the bugs probably did reduce crop yields. He said the soybeans probably should have been sprayed sooner, but farmers were trying to reduce their costs by conducting all their fungicide and insecticide treatment at once.
“Soybeans used to be something we planted and went and tended our cotton and corn,” Cook said. “Now, all the time it’s a few more dollars we’ve got to throw out in the field.”
But Cook doesn’t have to drive to a soybean field to find kudzu bugs.
“I have a white house, and when the day warms up they’ll be like gnats,” he said. They killed his chrysanthemums and ate his peppers and wisteria. He has to spray his window screens, soffits and window edges with pesticide.
“I have a kudzu bug graveyard around my house,” he quipped. They even get under the straps on deer stands.
“It would be great if we could get rid of them,” Cook said. “But they’re here to stay.”