Invasive spotted lanternfly may not damage hardwood trees as previously thought

In 2012, the spotted lanternfly (Lycorma delicatula) made its way to the United States from China, sparking concerns among scientists, land managers, and growers about the potential damage this sap-feeding insect could inflict on native and commercial trees. However, long-term research led by Penn State suggests that hardwood trees like maple, willow, and birch may be less vulnerable than initially feared.

Kelli Hoover, a professor of entomology at Penn State, explained, “Since the lanternfly was first introduced to the northeastern U.S., the question has been, ‘How at-risk are our forests?’ 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 research, published in the journal Environmental Entomology on August 29, aimed to assess the long-term effects of spotted lanternfly (SLF) feeding on hardwood trees. Researchers constructed large enclosures containing various tree species, including the insect’s favorite food, the non-native tree-of-heaven (Ailanthus altissima), as well as native trees like silver maple, weeping willow, and river birch. Some enclosures contained tree-of-heaven to observe its influence on the feeding pressure on native hardwoods.

Within these enclosures, researchers exposed trees to different densities of spotted lanternflies throughout their lifecycle, from eggs to adults. They monitored various factors, including leaf gas exchange, nutrient concentrations important for photosynthesis and growth, and tree diameter growth over four years.

The study found that increased feeding pressure from spotted lanternflies led to reduced levels of key nutrients, which significantly affected tree diameter growth during the first two years when feeding pressure was most intense. However, in the third year, when feeding pressure decreased, native trees recovered while tree-of-heaven’s growth remained stagnant. Leaf gas exchange did not show significant differences among the treatments.

The study represents a worst-case scenario in which spotted lanternflies fed on the same trees for four consecutive growing seasons. However, in natural settings where these insects move frequently among host trees, researchers do not expect significant negative impacts on forest or ornamental trees. Hoover emphasized that these findings could offer relief to growers and suggested that the cost of treating trees with insecticides might not be justified given the insects’ mobility.

The research received support from the U.S. Department of Agriculture and the Pennsylvania Department of Agriculture.

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