‘We may never again see the big populations that we saw in 2009 and 2010’
The headline that swept the country six weeks ago seemed too good to be true: “Polar vortex may have killed 95 percent of stink bugs, Virginia Tech researchers say.”
Seriously, who in Rappahannock County wouldn’t dance a jig to have only five brown marmorated stink bugs instead of a hundred dive bombing their lamp shades, dinner tables and bed sheets?
“That was me,” Virginia Tech entomology professor Thomas Kuhar tells the Rappahannock News, explaining how his outdated comments from a 2014 experiment — when researchers placed an insulated bucketful of stink bugs outdoors in advance of a prolonged cold snap — were erroneously inserted by a Washington, D.C., newspaper reporter into a 2019 polar vortex story.
And the misinformation signaling the demise of the putrid pests spread as fast as . . . well, stink bugs.
It’s true, 95 percent of the experimental stink bugs never crawled alive out of the now-infamous bucket. Which led researchers to believe that the 2014 polar vortex did indeed kill off large numbers of other outdoor stinkers (they mostly winter in trees) that didn’t choose to hibernate in warm attics or horse blankets.
Subsequent research revealed, however, that the shield-shaped stink bugs possess an uncanny ability to adapt to whatever gets thrown their way — polar vortexes included — and in due time their population numbers rebounded to previous levels.
“I’ve been researching them since 2010, so I’ve seen them a good nine years,” says the professor, who when not lecturing in the classroom or studying in the field keeps busy as founder and president of the Virginia Entomological Society and as a lifetime member of the Virginia Academy of Science. He’s also associate editor of the Journal of Integrated Pest Management and Focus on Tomato-Plant Management.
In other words, he knows his stink bugs.
“The bottom line is this bug does not survive severe sub-freezing temperatures really well. The bug knows it and [for that reason] gets into our houses,” Kuhar explains. “So we will see suppression when we have severe cold spells. The percentage of the population making it into a nice shed, nice horse blankets, do just fine. Those that get into an attic, get into insulation [also survive].”
As for “the proportion of the population that finds good shelter versus the ones [wintering] in dead trees, with cold temperatures there will probably be a drop in the population,” he says. “But it does rebuild.”
As witnessed time and again following prolonged periods of frigid weather in Rappahannock.
“The Appalachians are just ideal habitats for this insect we have found,” says Kuhar, particularly compared to Virginia’s coastal regions, where large populations “never established. Populations in coastal plains . . . don’t have them to the degree you would see in Rappahannock County.”
Polar vortexes aside, the professor does offer some “exciting news — kind of a three-fold natural enemy effect that is happening with the bug that is suppressing its populations.”
So significantly, says Kuhar, “We may never again see the big populations that we saw in 2009 and 2010, when [stink bugs] increased in the mid-Atlantic in unbelievable numbers.”
He explains that after the stink bug first appeared in the United States (between 1998 and 2001) its “natural enemies” didn’t initially recognize the creature native to China, Taiwan, Japan, and the Korean peninsula. As a result, its population exploded, especially here in Virginia.
“For a good decade now, some things have learned to feed on it,” Kuhar continues, including a number of vertebrates (chickens among them) that to some degree are “keeping populations in check.”
“They’re a little hot-tasting,” the professor observes, so stink bugs aren’t for everybody.
Also entering the equation in these mid-Atlantic states is the trissolcus japonicus — or “samurai wasp” — which while also native to Asia has somehow made its way to America in the last few years. The professor describes the samurai wasp as a “significant enemy” that could have “huge ramifications on the bug’s populations.”
In addition, researchers like Kuhar have started finding “diseases in the guts” of stink bugs, so as he describes it “natural control is starting to happen. I’m sitting here watching it happen.”
Finally, agricultural pest management programs are proving beneficial for countless farmers whose crops have been damaged by stink bugs, which are now raising havoc as far away as California.
“Biologically a lot of neat things are going on right now with test management strategies,” says the professor, including so-called “ghost traps” — or ghostly-looking pieces of horticultural net containing insecticides and stink bug aggregation pheromones (the foul-smelling chemical substance released by stink bugs when confronted with danger).
He likens the nets, which are often hung in trees or draped over fences and posts, to a “lure that draws in huge numbers of the bugs.”
“The bugs walk on it and pick up a lethal dose,” describes Kuhar, pointing out that Virginia Tech is playing a big role — from Blacksburg to Winchester — in studying stink bug repellents.
Not changing, of course, are the months of the year when stink bugs are the most active.
“In the fall, actually right at the fall equinox . . . they’ve got a biological switch,” explains Kuhar, where they go “from feeding on plants, apple orchards and soybean fields, to all of a sudden it’s time to shut down and seek shelter. Survival mechanisms — they know winter is coming.”
The stink bugs then assemble in large numbers wherever there are warm spots in the afternoon sun, such as on trees or the siding of houses and barns. As the weeks progress and it grows colder, the bugs begin making their way inside — whether it’s a natural or manmade structure — seeking a “cool, dark place that provides a little warmth, but not too much, to endure the winter,” he says.
“They stay in a big pack in the wintering shelter, and in the springtime they come out . . . and start life all over again.”