Although many homeowners have reported a greatly diminished population of the spotted lanternfly around their properties, the invaders from Asia known to attack more than 70 types of fruit and landscape trees and vines remain very much with us in at least 34 of Pennsylvania’s 67 counties.
That means the insect’s mass dispersal flights, which some have described as swarming, now are occurring as the first signs of late summer/early fall settle across the landscape.
Hundreds, even thousands, of the brightly colored, winged, adult-stage leafhoppers move in groups, although it’s not really swarming, according to Amy Korman, an educator with Penn State Extension who is well versed on the invasive insect.
“Swarming occurs when certain insects move in aggregations when stimulated by chemical and environmental cues,” she explained. “With spotted lanternflies, there may be some trigger that causes individual lanternflies to take to flight, but we have nothing to suggest these are deliberate formations of groups.”
In areas of smaller populations, lanternflies also engage in flight activity, but it is not as noticeable compared to areas where the population density is very high and flying behavior is more pronounced.
Research continues into the behavior, but the current theory about the reason behind it revolves around the need to find food, according to Kelli Hoover, professor of entomology at Penn State.
As early fall arrives, the spotted lanternfly’s preferred food, tree of heaven, goes into senescence, ending its movement of sap and dropping its leaves.
“We believe they leave an area when they individually sense that they have used up a food resource and need to find a better one,” Hoover said. “With prolonged heavy feeding on the same trees, such as tree of heaven, the food resource may be exhausted, and this motivates them to move to find other suitable food.”
That behavior might partially explain why in areas where populations were high, there are not many again the following year. However, after trees “recover,” high populations may again occur in that area.
Being in the vicinity of one of the lanternfly’s mass movements can be alarming, especially for people unfamiliar with the pest. But the insects do not bite or sting, they are not trying to get into homes or other buildings to overwinter, and the behavior lasts only a few days.
“The adults will die with the killing frost,” she said. “The only life stage that overwinters are the eggs. While sooty mold from honeydew produced by spotted lanternflies feeding in trees above structures can cause discoloration, the insects will not chew on the wood in the walls or otherwise hurt the structure.”
The most worrisome aspect of the spotted lanternfly’s movements is the potential for spread to other regions.
“When they are attracted to storefronts and the tall canopies over gas station pumps, there is potential for them to get into vehicles and items that are being transported, which could allow them to spread to new areas,” Korman said. “It’s important for everyone traveling in spotted lanternfly-infested areas to check their vehicles before leaving.”
Also, the public’s inclination to throw pesticides at any large mass of insects or any bothersome insect can lead to complications in the wake of a mass movement by spotted lanternflies.
“Some insecticides used on the outside of structures have a few weeks of residual activity, but new spotted lanternflies could keep coming, so spraying likely won’t completely eliminate them,” said Emelie Swackhamer, a horticulture educator with Penn State Extension who has been studying the spotted lanternfly since its discovery in 2014 in Berks County.
She also advises against the use of home remedies such as dish detergent concoctions and the like.
Instead, she suggests using mechanical methods, such as swatting and stomping, to destroy as many insects as possible.
“When you’re dealing with one of these flight events, keep in mind that it won’t last long,” Swackhamer said. “As unpleasant as it is, you just have to wait it out.”
For more information on the insect, visit the Penn State Extension Spotted Lanternfly webpages.