Scientists Along the East Coast Face Challenges in Spotted Lanternfly Research

Dr. Julie Urban might have the largest collection of planthoppers, a superfamily of insects known as Fulgoroidea, in the world. Her travels have taken her to places such as Borneo, Peru, Costa Rica, and Ghana, and the massive freezer she opens as she wanders around her lab is filled with thousands of specimens. Urban is an associate research professor in the Department of Entomology at Penn State University's  College of Agricultural Sciences, and though she is an expert in her field, one planthopper in particular has consumed her work for almost a decade: the spotted lanternfly.

The spotted lanternfly (Lycorma delicatula), or SLF as many scientists call it, originates from China and is also found in some countries in southeastern Asia. An infestation of the insect was first discovered in the United States in 2014, with the first sighting reported from Berks County, Pennsy4lvania. According to New York State Integrated Pest Management (NYS IPM) at Cornell University, the SLF is thought to have entered the country via a stone shipment in 2012, and is now considered an invasive species. It has earned a reputation as a villainous insect, with campaigns and requests from states to kill the insect on site spreading all the way from New York to North Carolina.

The SLF is notorious for threatening crops, and is especially drawn to grapevines, hops, and tree species such as the tree-of-heaven, an invasive tree, and black walnut. According to Brian Eshenaur, the Senior Extension Associate at NYS IPM, the spread of the SLF was slow at first, but growing numbers of infestations eventually began worrying members of the agricultural community. Eshenaur now helps manage a national map that tracks the spread of the SLF and helps oversee outreach for New York State.

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“Our grape growers got concerned when they saw the damage that was occurring to vineyards in Pennsylvania,” Eshenaur said. “They were concerned about its movement and how close it was getting to their vineyard. So it was helpful to have that map for them. We've been watching it, you know, for a good  six, seven years now.”

To Urban, the SLF marks one of the more peculiar insects she has ever explored. Many others share this sentiment, for example, many scientists have found it easier to rear specimens in the lab rather than perform tests in the wild. This is due to the fact that the SLF often moves constantly, an issue that has not only frustrated scientists in terms of performing experiments themselves, but has also meant that no one has been able to define what a single population size of SLF is – something integral to any scientific test or paper.

“Lanternfly moves so much throughout its life cycle, and it can hitchhike at any life stage, even as an egg mass, anywhere where it’s really been detected, once people have looked further, it’s been there at least 1-2 years already,” Urban said.  “And so this is the real problem. How do you come up with a good monitoring tool for the insect?”

Because the SLF consumes such a broad diet across all life stages, the insect often diffuses across an environment, making them difficult to locate. Urban mentioned that to combat this, early detection methods are integral to research, and discussed options such as environmental DNA (eDNA), which tracks cells that organisms shed into various environments, and detector dogs.

Dr. Kelli Oten, assistant professor and extension specialist at North Carolina State University, also mentioned the benefits of detector dogs to increase early detection methods. North Carolina is the southernmost state to which the SLF has spread within the United States, meaning much of Oten’s research is in its beginning stages. Plant Pest Administrator for the North Carolina Department of Agriculture & Consumer Services Joy Goforth aids the program for SLF detector dogs and their training.

“North Carolina has two dogs that are trained to sniff out the Spotted Lanternfly,” Oten said. “Our vision is only so good, and a dog's nose is much better. So they get one of the detector dogs out there and they sniff around. They can sniff out the egg mass, the nymph, or the adult.”

Before the SLF made its way to North Carolina, scientists in the state were still spreading the word about the invasive insect to allow for more proactive measures.

“We did a lot of outreach trying to make people more aware of the issue – that it was coming our way and trying to get people to be aware of what it looks like so that if they saw it, they knew to report it and knew where to report it,” Oten said. “Now that it is here in North Carolina, my role is still that, but I’m also taking on research as well.”

For Oten, the frustrations with the SLF are not only due to their spread and detection difficulty, but also because North Carolina faces unique struggles due to its warmer temperatures compared to other states the SLF has impacted. Oten’s research studies the phenology, or the timing of the SLF life cycle, and she estimated that the SLF would emerge sooner in North Carolina than in other states. She also said that she would like to study the new plants that the SLF may attack in order to get a handle on the range of the insect.

“Generally their [most insects] reproduction is faster when temperatures are warmer,” Oten said. “They’re poikilothermic, meaning they’re basically cold-blooded and their development is directly tied to temperatures. And we think that is the case with spotted lanternfly as well.”

One of the peculiarities that Oten has seen is the appearance of egg masses in North Carolina at the same time as other states, but the emergence of adult SLF at an earlier time within the state compared to other areas of the country. Because egg laying is dependent on day length rather than temperature, Oten said that SLF will lay eggs in preparation for the winter, however, what she does not know is if SLF will emerge sooner due to temperatures increasing within the state faster than northern states.

Another issue Oten faces is the suspected increase in temperatures during winters due to climate change. Most of the time, many states rely on cold snaps to kill the majority of an invasive species population, but due to potential increases in temperature, populations may become higher than they would be otherwise.

Regarding predators of SLF, Anne Johnson, a Ph.D. student in Dr. Kelli Hoover’s lab at Penn State University, is actively researching what defense mechanisms SLF may use in order to protect itself. Her research studies toxin sequestration, or how insects remove toxins from their host plants, within SLF and its impacts on predator-prey interactions. Johnson is specifically studying the preferred host of the lanternfly, the Tree of Heaven, another invasive species within the United States. Johnson believes that SLF may have evolved to store bitter-tasting compounds from the tree in order to defend itself against predators.

Johnson’s research began with a community science project in 2020, where reports from the general public helped her collect data. She began a Facebook page titled “Birds Biting Bad Bugs” with the goal of collecting community data on what insects were feeding on the SLF. From that data, Johnson was able to discover that arthropods might be able to handle the chemical defenses in SLF more often than many other invertebrates.

Johnson also has raised SLF within the lab and reared the insect on both Tree of Heaven and plants such as grape and cucumber. She has used these specimens to begin experiments with house wrens, recording the reactions of birds to SLF raised on Tree of Heaven versus other plants that lack these bitter tasting compounds. Johnson said that there are over 100 nest boxes for this study around Penn State, University Park’s campus and properties.

“We did some bird experiments where I put those differently raised spotted lanternfly into suet blocks, and the birds would peck the ones that did not feed on Tree of Heaven more often than they did on the Tree of Heaven ones,” Johnson said.

Hoover, who is a professor of Entomology and whose lab Johnson works in, studies the biology and ecology of invasive species, and has also been studying this insect for many years. Penn State is involved in a group called the Special Crop Research Initiative (SCRI) under the USDA which involves about seven universities in the US. These institutions have been able to receive grants in order to study the SLF.

Hoover has had a hand in many different experiments, including studies regarding how temperatures impact SLF life stages, the host range and detection of the insect, movement patterns, and how SLF feeding impacts host plants. Hoover mentioned that what many scientists are beginning to do now is focus on conservation efforts and biocontrol  in order to attract more natural predators of SLF to areas in which the insect is found.

“If I had a vineyard, I would be planting the kinds of flowers these natural enemies like to feed on for extra protein and nectar for energy all around my vineyard,” Hoover said. “Because they’ll be spraying in the vineyard, but if you’re not spraying outside the vineyard you might be able to raise up some natural enemies close by. Nobody’s really had very good success with taking praying mantis egg cases and putting them out, but it’s worth trying on a limited scale.”

Urban also emphasized the work her postdoctoral scholar, Holly Shugart, has been doing with the insect. Shugart is one of the only people who has expertise using SLF in experiments involving electrical penetration graphs, or EPG. EPG studies the interactions insects have with host plants, and the graph tracks wavelengths that are correlated with behaviors such as saliva excretion or the ingestion of the plant. Shugart’s EPG system includes a wire connected to a plant, typically Tree of Heaven, with the other end connected to the insect via a tiny drop of glue.

The electrical current Shugart uses is measured in millivolts, meaning it is not able to hurt the insect in any way. When the SLF inserts its stylet, or mouthpart,  into the plant, Shugart is able to track their interactions with the host plant. Through this research, Shugart is able to recognize the behaviors of the insect, as well as how long it may spend feeding on a host plant, and how exactly it may interact with these plants in the wild.

Urban later mentioned that though there is extensive research on the SLF from scientists across the country, there is still a lack of knowledge regarding solutions to protecting crops and other plants from the insect. Since the insect moves around so rapidly, and can hitchhike from place to place across life stages, it is difficult for scientists to define what a population, or number of SLF living in a specified area, may be in any given place, making many experiments done in the wild virtually impossible in terms of generalizing behaviors and data.

“In terms of management, if you’ve noticed, no one’s ever published anything about how effective any of the control measures are. It’s not there, because what is a population?” Urban said.

As of now, SLF maintenance and crop protection strategies are still under investigation, but as concerns grow globally about damage to food systems, the pressure is mounting on scientists. Shugart and Urban mentioned that there is currently a partnership between scientists at Penn State and in New Zealand. Though SLF has not entered New Zealand yet, there is a growing concern in the country that the insect will cause damage to crops such as kiwi and stone fruits. Because many of these crops are imported into the US, scientists in New Zealand have sent kiwi plants to Penn State in order for scientists at the university to use them in SLF studies. Urban and Shugart both mentioned that states and countries that prepare early and participate in through research will be better prepared for the insect if and when it spreads further.

“I’ve spent the last 20 years of my career  chasing the latest invasive insect,” Shugart said. “We did more work than was required because we want them to be prepared.”