The Spotted Lanternfly (SLF) is an invasive insect first sighted in southeastern PA in September 2014. Despite its common name, it isn’t a fly, but a plant hopper. Researchers believe that the SLF came into Philadelphia from China in egg form on a pallet holding a shipment of rocks. Adult SLF are about 1” long and ½” wide when at rest. They have piercing, sucking mouth parts, large wings and look somewhat like butterflies or moths, but they are primarily hoppers, and do not fly well. Both nymphs and adult SLF cause damage when they feed, sucking sap from stems and leaves. The adult SLF prefers the invasive tree of heaven (Ailanthus altissima) as its primary host. The nymph stages will use numerous plants as hosts. Feeding takes place from April until November or the first hard frost. Basically, if SLF is alive, it will be feeding. Adults and nymphs combined have the potential for major economic harm in North America, as prime targets include grapes, peaches, and other stone fruit, apples, and various trees commonly harvested as lumber.
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The SLF completes its life cycle in one year. Adults mate and lay eggs in late summer, but do not survive the winter. The eggs remain viable until the following spring, when they hatch. Eggs (which were laid the previous year) hatch into nymphs in April and enter a cycle of climbing/descending host plants. Nymphs climb to feed on leaves and branches, but often fall due to wind or other obstacles. They will repeat their climbing activity to reach their preferred food again. There are 4 instars of SLF nymphs. After hatching from eggs in spring, the nymphs mature through the 4 stages (instars), until they develop into adults, usually in mid-summer.
By the black color, these would be early instar SLF.
The first three instars have a black body and legs with white spots. The fourth instar retains the spots but turns red just before becoming adult. Nymphs are wingless. Each successive instar is larger than the previous one.
Red color indicates 4th instar SLF.
We all need to learn to recognize signs of infestation. Here’s what to look for:
adult insects on host trees (Ailanthus) in late summer and fall,
SLF adult, good detail on the wings.
brownish gray egg masses on or near host trees until they hatch in spring,
Egg mass (bottom), adult SLF (center), hatched egg cases (top).
dark streaks or sap flowing down the bark of the host tree (caused by SLF piercing the phloem to feed),
honeydew secretions near the base of the tree (adult SLF produce large amounts),
The white area is honeydew, and may also be associated with sooty mold, which can form on the honeydew.
and finally, bee and wasp activity near the honeydew secretions.
Where are SLF known to exist in North America? The PA Department of Agriculture has quarantined 13 counties in southeastern PA. However in November 2017, one (dead) individual was discovered in Delaware county, NY. Also in November 2017, one SLF female was discovered in New Castle county, Delaware. And in January 2018, a property owner in Frederick county, VA found numerous adults (dead) and egg masses. The property owner has burned the host ailanthus trees in an effort to destroy the invasive insect. (I have requested an update on the VA sighting from my county extension agent.)
How does an insect that doesn’t fly well extend its range? Left to its own devices, the SLF would likely extend its range very slowly. But the least mobile of the life cycle stages, the egg stage, is being transported by unwitting humans. SLF egg masses are inconspicuous, and females will lay them on virtually any surface: trees, lumber, tarps, yard furniture, vehicles. The egg masses become stealthy hitchhikers, and are moved distances far beyond the SLF’s own capability for travel. Combine that with the fact that their preferred host plant, Ailanthus, is an invasive itself that tends to grow in disturbed areas such as around parking lots or along highways and railroad tracks. Female SLF that are ready to lay eggs tend to drop onto the nearest convenient surface and deposit roughly 30 to 50 eggs. Think about this – an SLF female could very easily deposit an egg mass on the side of an 18 wheeler, or on a railroad car. And Ailanthus, the preferred host of adult SLF, is already growing in 44 states. You can visualize how easily this invader can spread. The current range of SLF in PA can be seen here. (This is a pdf map.)
It is unclear to what extent natural enemies will control L. delicatula in North America. Natural enemies of other plant hoppers in Pennsylvania, including Dryninidae (Hymenoptera) and Epipyropidae larvae (Lepidoptera), do not appear to control L. delicatula (Barringer, personal observations). Chemical defenses acquired by feeding primarily on the tree of heaven deter many generalist predators (Xue and Yuan 1996) and birds have been observed vomiting after consumption of this insect (Kang et al. 2011). Relatively few parasitoids are known to parasitize immature stages of fulgorids. The parasitic wasp Anastatus orientalis (Hymenoptera, Eupelmidae) is an egg parasitoid of L. delicatula in China, and is considered to be an important biocontrol agent as its parasitism rates reach up to 80% in some regions (Choi et al. 2014).
However, this parasitoid does not occur in North America. More information, and a list of the references quoted above is available in this open access document. Also contained in this document is a table of host plants, which is too long to reproduce here, and a graphic showing all 4 instars at once.
Here is the Integrated Pest Management (IPM) strategy from Penn State extension:
Locate Ailianthus altissima trees on the site. For reasons not understood, spotted lanternfly seem to prefer some individual Ailanthus altissima trees over others. Try to identify the specific Ailanthus trees that are most attractive to the insects, based on how many are feeding on them.
Destroy approximately 90% of the Ailanthus altissima trees, leaving only a few that are most attractive to the insect. They will serve as "trap" trees. It is recommended that you try to kill all the female Ailanthus altissima trees, because they produce seed and contribute to the spread of this invasive tree.
Be careful handling Ailanthus altissima wood, leaves and branches. Chemicals in the sap of this tree can cause headaches, nausea and possible heart problems. Wear gloves and protect yourself from exposure.
When you cut down Ailanthus altissima trees, they will sprout profusely from the stumps and can grow back in a few years. Because they regenerate so easily, it is recommended that you treat the stumps with an herbicide to kill them and prevent them from sprouting new shoots.
Herbicides that are labelled for this use usually contain one of the following active ingredients triclopyr, dicamba, imazpyr or glyphoshate. Use the herbicide carefully and according to directions on the label. Alternative methods for using herbicides to kill Alianthus altissima trees include foliar sprays, basal bark applications and a method called frill application or "hack and squirt".
The Penn State Extension publication-- Herbicides and Forest Vegetation Management, has more information about these methods. Whichever method you choose, remember that you will have dead Ailanthus trees which may eventually have to be removed.
Treat the remaining Ailanthus altissima trees with a systemic insecticide that will move throughout the tree. The insecticide must be applied according to the label and at the right time of year for the trees to absorb it. When spotted lanternflies feed on correctly treated trees, they will die. Systemic insecticides that are labelled to treat ornamental trees usually contain the active ingredients dinotefuran or imidacloprid. The PDA is using dinotefuran in their IPM strategy.
Treating only a few trap trees with a systemic product can reduce the amount of insecticide released into the environment and may help conserve beneficial insects.
While I have not seen SLF on my property, I have had occasion to remove Ailanthus trees. The method described above works, but to successfully prevent regrowth the herbicide has to be painted on the freshly cut stump. Ailanthus have the ability to seal over a fresh cut very quickly, so you must literally put down the saw, and begin painting the stump. This is one of the few uses that I have for herbicides. If I can find an alternate to applying herbicides , I always choose that. In the case of systemic insecticide treatment described above, there is also an option that does not involve spraying chemicals. Apply sticky bands to the remaining trap trees once you have cut the first 90% down. The sticky bands are very effective, and they trap the insects as they crawl up and down the tree trunks.
Sticky bands are wrapped around the trunks of host trees.
I spend an inordinate amount of time worrying about invasive insects. I see some parallels between the SLF invasion, and the invasion of the Brown Marmorated Stink Bug (Halyomorpha halys) in the late 1990s. They are both members of Hemiptera (true bugs) that entered the US on shipping or packing material. Both came in through the port of Philadelphia and were first discovered in eastern PA. Both attack agricultural crops and can do great economic harm to susceptible crops. Both are native to China, and most important, both arrived without any of their natural predators.
Presently SLF occurs in a relatively small area. It is still possible to contain them, it may even be possible to eradicate them, but USDA and officials of state departments of agriculture can do only so much. We all must learn to recognize the insect, both adult and all 4 instars. Learn to recognize signs of SLF damage. If visiting or driving through areas known to be infected with SLF, do not park or leave personal items beneath a tree of heaven. Even if you don’t see any SLF, it only takes one female to leave an egg mass on your car or personal property. Inspect your vehicle and personal property thoroughly before leaving an infected area. Don’t move firewood, outdoor furniture, or stone out of the infected area. And if you spot any SLF or egg cases outside the areas where they are known to exist, collect a sample or take a photo if a sample isn’t possible, and submit to your local extension office along with detailed locational information.
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