Spotted lanternflies’ love for tall, vertical surfaces as the perfect launching spot for their weak flights is the reason piles of the insects are showing up around places like office buildings, according to a Penn State researcher.
“They often end up at the base of buildings or the sides of buildings because they orient to tall, vertical surfaces,” said professor of entomology Kelli Hoover. “They’ll probably move on.”
The invasive insect arrived at their current location while searching for new sources of food. Sidewalks and parking lots around office buildings usually are not fertile spots for the plants from which the lanternflies such sap.
When the leafhoppers sense they have nearly depleted the food in their current location, they climb high onto the nearest vertical structure and launch into a clumsy, weak flight, she said. Nearly all lanternflies in a spot will carry out that same maneuver in a relatively small window of time, but they tend to launch in groups of 10, 50, 100 or so rather than in a mass migration in one giant swarm.
“They’ll take off in large numbers and they’ll all leave the area to go find a new location, sometimes several miles away,” she explained. “They’re all getting cues within a day that their food source is running out. Then they’ll move onto other plants that are still going strong.”
While the sap flow in tree of heaven may be shutting down at this time of year, other trees like red maple continue to pump the liquid nutrition the lanternflies seek.
The insects are strongly attracted to tree of heaven, another invasive species that has been widely planted as landscaping trees and has escaped into the wild, but agriculture interests worry about the many other, economically important plants they will attack.
“The spotted lanternfly uses its piercing-sucking mouthpart to feed on sap from over 70 different plant species,” according to the Pennsylvania Department of Agriculture. “It has a strong preference for economically important plants including grapevines, maple trees, black walnut, birch, willow and other trees.”
The landscaping around a tall building might also explain the lanternflies’ sudden appearance if that landscaping includes anything on that list of more than 70 plants.
It could also be part of the explanation for masses of lanternflies showing up in drive-thru lanes at fast-food and coffee shops and in parking lots that are not adjacent to tall buildings, but Hoover thinks that might result from the weak-flying insects being pushed there by winds.
Winds and thermals likely also are the reason that the insects are being seen at mountaintop hawk watches and over sports stadiums such as the Pittsburgh Steelers’ Acrisure Stadium and the Philadelphia Eagles’ Lincoln Financial Field.
That pattern of depleting a food source in one area and them moving on en masse to a new area also explains the recent observations of Amy Korman, an educator with Penn State Extension.
“There were spotted lanternflies everywhere” in the Harrisburg area when she was in town over the weekend.
“It’s like days of yore in some of our area,” with masses of lanternflies climbing on all surfaces and flying clumsily about, she noted.
But in other areas, where the lanternflies were abundant last year or the year before, like the building that houses her office in Northampton County, this year there are far fewer of the insects.
“There still here, but they aren’t in the thousands,” she noted.
While researchers have yet to determine if that boom-bust year-to-year pattern in lanternfly populations will continue to be a hallmark of the insect, anecdotal evidence shows it has been happening in many areas of Pennsylvania.
Korman noted that a pattern of a population building over several years, until damage is widespread across an area, and then crashing is a decided fact for a species like the spongy moth, which was formerly known as the gypsy moth.
“It’s well understood and well recorded, but we don’t know that about the spotted lanternfly,” she commented. There hasn’t been enough research over the long term to make the determination.
The hope that the lanternfly population dropped drastically this year in an area and will remain low may be wishful thinking.
“Are the populations going to build up again?” she commented. “We’ll just have to wait to see.”
For the rest of this year, they could show up suddenly anywhere, until the first hard frost takes out the winged adults.
Contact Marcus Schneck at mschneck@pennlive.com.