Widen the scope

The ever increasing and seemingly unstoppable population of the spotted lanternfly (SLF) (Lycorma delicatula) is significantly embedded in Delaware, Maryland, New York, New Jersey, Pennsylvania and Virginia. While many authorities make an almost continual reference to tree of heaven (Ailanthus altissima) as the preferred food plant for this insect, I would submit an adjustment to the word “preferred.” Field observations in Southeast Pennsylvania shows Ailanthus is common and is a frequent host to the SLF, but the plant is not necessarily plentiful in some areas and population densities can vary from nearly nothing (Bucks County) to extensive (Montgomery, Chester and Delaware counties). However, the spotted lanternfly is quite adaptable in finding new horizons on which to feed. Adaptation has led them to silver maple (Acer saccharinum), which in many quarters is more plentiful than Ailanthus. Oddly, the spotted lanternfly does not rely on other maples and generally leave red maple (Acer rubrum), sugar maple (Acer saccharum) and Japanese maple (Acer palmatum) alone. They do seem to like Acer platanoides, an invasive exotic. SLF has no interest in anything in the Fabaceae family (Cercis, Gleditsia, Gymnocladus and Cladrastis). They have no interest in the Asian flowering cherries nor the Northeast native Prunus serotina. However, the pest does have a strong affinity for things in the Vitaceae family and in lower Southeast Pennsylvania there is a cornucopia of things to go after in that family. It seems almost negligent to discuss Ailanthus and the spotted lanternfly and leave out the members of the grape family. Muscadine grapes (Vitis rotundifolia) reach a northern limit in Virginia but then parade all the way down into central Florida. Vineyard owners tell me that SLF is a major pest in their operations going after wine grapes. American porcelain vine (Ampelopsis cordata), a North American native, is an SLF favorite. But its cousin, the invasive Chinese porcelain vine, (Ampelopsis brevipedunculata) covers extensive areas in the Northeast, Southeast and portions of the Midwest and is the mother lode when it comes to feeding SLF. Casual observation would suggest that porcelain vine is an entrenched, significant component of almost any natural area with varying levels of disturbance. For agricultural authorities to suggest wholesale war on tree of heaven and leave out porcelain vine is woefully insufficient.

Another plant keen on the SLF’s want list is Aralia spinosa, as SLF will flock to the new shoots in the spring while in the instar stage. This native plant occupies a vast area of the Northeast, Southeast and Midwest and is common in the Philadelphia metro area. It is easily spread by seed and is stoloniferous, which forms large colonies, much like tree of heaven. Spotted lanternfly was once dependent on Asian species of plants but has significantly altered its feeding habits to take advantage of some native plants and introduced ornamentals. They like cultivated roses, especially Knock Out Rose, but leave native roses alone, including Rosa virginiana, R.caroliniana and R. nitida. Perhaps this is because those roses have distinct foliar odors that the cultivated roses do not have. SLF instars also have an affinity for the mulberry family (Morus sp). Another clear host is Salix alba ‘Sericea’. It is my observation that aside from porcelain vine, the silver willow is by far the most frequented plant for the instar stage of the SLF. It is not clear if other willows are also on the menu. A rather surprising find is that SLF has preferences for our native black walnuts (Juglans nigra) but not butternut (Juglans cinerea). It is clear however that the insect is adapting fast to what's at hand.

Photos by Bill Barnes

What is abundantly evident is that the SLF instars are looking for plant tissue that is in soft new growth. They prefer new, green, smooth bark and generally have no interest in rough bark or bark that is formidable in any way. They avoid many plants that harbor toxins, except for Styrax japonicus which has considerable amounts of saponins in their tissues. Perhaps this is not by chance. The instars change color from black with white spots to bright red with white spots. As adults they are very colorful with mixtures of red, blue, white, black and gray. Vivid coloration in insects often is a clue to an inherent toxicity. Perhaps what is driving them to certain plants is the acquisition of the plant poisons that they can ingest and incorporate to protect them from predators. This seems more than anecdotal as assassin bugs will readily approach them only to be repelled after reaching a close encounter. Cicada killer wasps have an interest in SLF adults, and they do kill some of them but not on a grand scale. This indicates that potential predators might be limited possibly because they are so vastly outnumbered.

Spotted lanternfly is a hitchhiker with considerable evidence of its egg laying abilities on smooth metal equipment such as the under carriages of trucks, buses, automobiles and, more than likely, railroad equipment. The extent of this is probably greatly underestimated. Amtrak regularly travels from Philadelphia to points west. While waiting for an Amtrak train, one such volunteer traveler flew into my wife's purse as she was headed to Pittsburgh. Had I not spotted it and killed it; this hitchhiker would have easily taken a ride to Pittsburgh. This was in the fall and it could have easily laid eggs and set up shop in Pittsburgh. This capability of the insect to utilize rapid transit of all kinds makes it virtually unstoppable.

The case for control

Are insecticides a possible solution? Maybe for a localized occurrence, but as a practical matter they are largely ineffective — except in agricultural situations. There are too many insects in too many areas not reachable by pesticides, nor is there money available to go after the insect in such a wholesale fashion. There are limits to modeling as a tool considering how widespread the insect is. Areas that are not cultivated nor accessible by any control measures such as egg laying on the underside of roof overhangs, natural areas, hedgerows and state and local parks act as reservoirs for continual repopulation. Killing Ailanthus is a reasonable proposal, but not practical because it will be an almost impossible task and will have almost no effect on the eventual spread of the insect. Killing off Ailanthus for SLF control will only increase the propensity to find new plant species to utilize. If the other plant hosts, such as Ampelopsis, Morus and Salix, are not controlled as well, there is little hope of success in controlling the SLF.

Where is the money to combat this pest and who is going to pay for it? Along the I-476 corridor between the Mid County interchange (I-276) and I-95 are thousands of Ailanthus along a distance of 15 miles through Montgomery, Chester and Delaware counties. Moving south to Delaware and east to New Jersey there are more likely tens of thousands to hundreds of thousands of these trees, along with tens of thousands of acres of porcelain vine which often occur in conjunction to the tree of heaven. The extent of control by any means is a small percentage of what is really out there. Due to propensity for the egg laying on smooth metal surfaces it is impossible to monitor all the railroad cars, trucks, buses, private trailers and other vehicles.

Money spent on non-effective measures should be redirected. The only recourse is to hit this insect with a disease, be it viral or bacterial. Perhaps Bacillus thuringiensisis a possibility. An introduced predator could well cause collateral damage on native insects. Emerald ash borer (Agrilus planipennis) will eventually burn itself out because its food supply of native ash will disappear, and it has not adapted to anything else. But spotted lanternfly does not hesitate to alter its feeding habits and it is here to stay. Germ warfare is the preferred option for control. All the other measures are essentially wasting time and money and will not be effective now or ever.

About the author: Bill Barnes is a horticultural consultant and has been in the nursery business for 45 years. He’s an active member of the International Plant Propagators Society, an IPPS Fellow and received the IPPS Award of Merit. Bill also teaches at the Barnes Arboretum at St. Joseph University in Philadelphia. He introduced Cercidiphyllum japonicum Tidal Wave and Morus alba Green Wave. bill@barnhortservices.com

Opinions expressed are those of the author and do not necessarily represent the views of GIE Media, Inc.