Penn State study says spotted lanternflies don’t damage trees, forests

Spotted lanternflies have overtaken much of Pennsylvania and are expanding their reach, but a new study reports that the invasive insects are doing less damage to trees than previously believed.

Research from Penn State recently published in the journal Environmental Entomology shows spotted lanternflies have no long-term effects on forests or ornamental trees. Short-term research initially said that lanternflies, which feed on several tree species, can reduce the growth of maple saplings, but the new study shows that trees recover and grow in subsequent years.

Spotted lanternflies are native to China and were first discovered in the United States in Pennsylvania’s Berks County in 2014. They have since expanded across Pennsylvania and beyond, and Southwestern Pennsylvania has seen swarms of the insects since 2019.

Penn State entomology professor Kelli Hoover said the new study “is the first to look at the long-term impacts of feeding pressure on Northeastern hardwoods, and our results suggest that we are unlikely to see big impacts on the growth of trees.”

The four-year study created a worst-case scenario that had spotted lanternflies feeding constantly on native trees, including silver maple, weeping willow and river birch, as well as the non-native tree of heaven, which is the favorite of lanternflies.

None of the trees in the study died.

The trees did see reduced growth for the first two years, according to the study, but the native trees recovered when feeding was less intense.

“In a natural setting where the insects are constantly on the move, we would not expect significant negative impacts on forest or ornamental trees,” Hoover said.

The tree of heaven was the only species that saw growth levels remain flat after the first two years of reduced growth. Tree of heaven is an invasive species from China.

Lanternflies tend to migrate across large regions and don’t tend to stay in the same area for long periods. While Southeastern Pennsylvania had large numbers of lanternflies in the late 2010s, the insects have largely moved out of that area and are now more prevalent in the Pittsburgh region.

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Predators such as praying mantises have also started to prey on lanternflies.

Experts have noted that spotted lanternflies have stressed plant life in the state, but don’t appear to be a danger to the ecosystem. Farmers may still want to remove the pests because they have damaged some crops, including grapes and apples.

The state Department of Agriculture recommends removing spotted lanternflies by stomping them, creating traps on trees and calling professionals when infestations are particularly bad.