Why are more spotted lanternflies in some areas of PA but not others? Researchers aren’t sure

Spotted lanternflies have returned in full force this year for much of the region and across Pennsylvania.

The invasive species is native to Asia and not “true flies” but instead a type of planthopper that is closely related to cicadas, leafhoppers, and treehoppers said Amy Korman, Ph.D. in entomology and Horticulture PSU Extension Educator.

They were initially observed in Pennsylvania in 2014 but were probably here a few years earlier after being accidentally introduced, she said.

But why do some regions seem to have large numbers of lanternflies when there were few in previous years, and why do other areas seem to have few compared to previous years?

Well, the answer to that question is still being researched.

Statewide, there have been 9,885 reports of spotted lanternflies through July 11 of this year, said Shannon Powers, press secretary with the Pennsylvania Department of Agriculture. In the same time frame last year, there were 4,827 reported sightings.

The success of spotted lanternfly populations is most likely related to environmental conditions, available resources like food and their biology, which is still being studied, said Korman.

While some places may experience ideal conditions for lanternfly population development over several years, Korman explains that a freeze or a dry spell at certain parts of their life cycle may affect the population. Lanternflies also move around a lot, but researchers are still learning about their behavior, Korman said. While they initially might be missing in one area, they are known to show up in larger numbers later in the season, she added.

“Right now, we do a lot of scientific speculation on what is happening with the various lanternfly hot spots in Pennsylvania,” Korman said.

Spotted lanternfly populations are measured by the Pennsylvania Department of Agriculture through survey programs it conducts across the state with staff from the U.S. Department of Agriculture staff. The public can report sightings using the SLF Public Reporting Tool.

Public reporters are largely an indicator of public awareness, Powers said.

Powers explained that some areas that have seen lanternflies for several years are reporting fewer because people are used to seeing them. In other areas where the insects seem to be less prevalent, more people are seeing them and reporting them, she said.

Data from the public reports is important and used to measure the insect’s spread from year to year, Powers said.

It is especially important to monitor and control the lanternflies’ spread in tourist attractions and other highly trafficked areas where people can give them a ride to a new location, Powers said, explaining that lanternflies can only fly short distances and spread large distances by “hitchhiking” in vehicles or using wind currents to travel up to a mile.

“They have not traveled on their own from Pennsylvania to places like Indiana where they’ve now been found,” Powers said.

Damage caused by lanternflies

Spotted lanternflies feed on over 70 different plants and as adults, they tend to prefer woody plants such as tree of heaven, black walnut, red maple, and grapes, explained Korman. They normally don’t kill trees although they have killed invasive trees called trees of heaven.

The insects feed on the carbohydrate-rich phloem fluid that the plant is moving throughout its structure to support growth and development, Korman said. However she mentioned that while a healthy tree should be able to withstand the stress of the spotted lanternfly feeding, it can be stressful to the tree and stress in plants can make them more susceptible to infections by plant pathogens and invasion by other insects.

One major thing that spotted lanternflies have damaged are grapevines in vineyards, as they are susceptible to the lanternflies, Korman said.

Korman and Powers agreed that no matter what stage lanternflies are in, they should be killed immediately.

Korman said eggs can be smashed or scraped, nymphs and adults can be smashed, swatted, or trapped by tree traps. Nymphs and adults are also susceptible to most pesticides but, people should look for Environmental Protection Agency registered pesticide that is labeled for the appropriate site such as ornamental trees and shrubs, or grapes, etc.

“The only good one (lanternfly) is a dead one,” Korman said.