Spotted lanterfly casts bad light on crop scene

Spotted lanternfly (SLF) is an invasive planthopper native to China, India, and Vietnam. It was first detected in the U.S. in Pennsylvania in 2014, most likely arriving up to two years earlier as egg masses on materials imported from China. Due to its highly invasive nature, it has been spreading quite rapidly and, as of February 2022, has been confirmed in Pennsylvania, New Jersey, Delaware, New York, Maryland, Virginia, Connecticut, Massachusetts, Indiana, West Virginia, and Ohio.

Adult SLFs are pretty large insects, approximately 1 inch long and ½ inch wide when resting and are brightly colored. When resting, adults fold their wings over their bodies and appear light brown to grey with black spots. SLF overwinter as eggs in egg masses that are greyish-brown, covered with a grey, waxy coating, and contain 30 to 50 eggs. In the spring and early summer, eggs hatch and SLFs go through four nymphal stages before turning into adults. SLF has only one generation per year.

Adults begin to appear in July and August. Males and females mate multiple times and females can produce one or two egg masses between September through November (or until they die from the onset of winter). Female SLFs lay egg masses on smooth-barked trunks, branches, and limb bases of medium to large-sized trees, as well as on smooth stone and other natural surfaces, and on man-made items such as yard furniture, cars, trucks, and farm equipment.

SLF has a large host range and potentially could greatly impact the grape, tree fruit, plant nursery and timber industries in the U.S. SLF nymphs appear to feed on leaves and branches of virtually any plant they encounter, often gathering in large numbers. In the fall, adult SLFs gather in large numbers on tree of heaven/paradise tree (Ailanthus altissima), willow, maple, birch, poplar, tulip poplar, ash, oak, grape, apple and stone fruit trees (e.g., cherries and plums). Tree of heaven, an invasive species native to China that grows in disturbed sites and along roadsides, is a preferred host for SLF adults for fall feeding, mating and egg laying,.

SLF adults and nymphs feed on a plant’s phloem (i.e., food conducting tissue), sucking the sap from young stems and leaves, and reducing the plant’s ability to photosynthesize. Affected plants often have weeping/oozing wounds on their trunks that eventually result in greyish-black discolorations. Damage can lead to weakened, withered plants, and potentially even plant death. In addition, SLFs excrete large amounts of honeydew which can cover stems and leaves and build up on the ground at the base of plants. Honeydew can become colonized by sooty mold fungi giving leaves and branches a blackish coating that can further reduce photosynthesis and contribute to plant decline and death. Oozing sap and honeydew also attract other insects such as wasps, hornets, bees, and ants.

SLF adults are poor fliers, but strong jumpers, and prefer to walk. Nymphs and adults gather in large numbers on host plants and are easy to find at dusk or at night when they migrate up and down tree trunks. SLFs are harder to find during the day as they tend to stay near the base of the host plants. Sticky tree bands can be helpful for monitoring for young SLFs, but less useful in detecting later stage immature and adult SLFs.

To date, SLF has not been found in Wisconsin. Because SLF has great potential to adversely affect the grape, tree fruit, plant nursery, and timber industries, preventing introduction of SLF into Wisconsin is very important. Accidental movement of egg masses poses the greatest risk for introduction. Therefore, watching for egg masses (as well as adults and nymphs) on any item that has come from areas where SLF is established is important to prevent the spread of this species.

If you suspect that you have found SLF, please contact the UW- Madison Insect Diagnostic Lab at idl@entomology.wisc.edu or DATCP at datcppesthotline@wisconsin.gov.

Christelle Guédot, is the Associate Professor of Fruit Crop, Entomologist and Extension Specialist with the Department of Entomology at the University of Wisconsin - Madison