UNIVERSITY PARK, Pa. — In 2012, when the spotted lanternfly arrived in the U.S. from its home in China, scientists, land managers and growers were concerned that the sap-feeding insect would damage native and commercial trees. New long-term research led by Penn State has revealed that hardwood trees, such as maple, willow and birch, may be less vulnerable than initially thought.
“Since the lanternfly was first introduced to the Northeastern U.S., the question has been, ‘How at-risk are our forests?’ said Kelli Hoover, professor of entomology at Penn State and corresponding author on the study. “So far, we haven’t had a good answer. Our 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 findings were published in the journal Environmental Entomology on Aug. 29.
To determine the long-term effects of spotted lanternfly feeding on hardwood trees, the team built large enclosures containing multiple species of tree, including the insect’s favorite food, the non-native tree-of-heaven, as well as native trees, including silver maple, weeping willow and river birch. The team included tree-of-heaven in half of the enclosures to determine whether its presence would influence the feeding pressure on the native hardwoods.
Within the enclosures, the researchers reared different densities of spotted lanternflies for all or most of their lifecycle, from eggs through adults, to see if the number of insects feeding on a tree would impact its growth and survival.
After the first two years, they reduced the density of the insects to see if the trees would recover. They monitored leaf gas exchange and concentrations of nutrients that are important for photosynthesis and growth for the first two years and tree diameter growth for the full four years.
“In the wild, we have seen that spotted lanternfly population numbers vary greatly from year to year on individual trees, and they move frequently among host trees,” Hoover said.
“Our study represents a worst-case scenario in which spotted lanternflies fed on the same trees for four consecutive growing seasons. While we did see reduced growth after two years of intense feeding, the native trees recovered when feeding was less intense. Importantly, over the four years, none of the trees died. Therefore, in a natural setting where the insects are constantly on the move, we would not expect significant negative impacts on forest or ornamental trees.”
The team found that increased feeding pressure from spotted lanternflies resulted in reduced key nutrients, which, in turn, markedly impacted tree diameter growth during the first two years when feeding pressure was the most intense.
However, in year three, when the feeding pressure was reduced, the native trees recovered while tree-of-heaven’s growth remained flat. Leaf gas exchange did not differ significantly among the treatments.
The U.S. Department of Agriculture and Pennsylvania Department of Agriculture supported this research.
(Information provided by Sara LaJeunesse, Penn State University.)
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