A beautiful menace is on the move in the United States. Polka-dotted, red-and-gray-winged insects are gliding along sidewalks, climbing over plants and crawling up buildings. Spotted youngsters are leaping away to avoid a sticky end at the bottom of a shoe.
Welcome to spotted lanternfly season.
Spotted lanternflies (Lycoma delicatula) are an invasive plant hopper. They’re native to parts of China, India and Vietnam. But for more than a decade, they’ve been making their way across the Mid-Atlantic and northeastern United States. And they’re headed west. Some researchers worry they might soon reach California.
A cache of eggs likely first arrived in 2012 as part of a shipment of landscaping stone. This was in Pennsylvania’s Berks County. The insects weren’t detected, though, for two more years. Today, they’ve set up thriving populations in 17 states and counting.
With this spread, spotted lanternflies have found plenty of plants on which to feast, especially grapevines. This has sparked worries that some farmed crops could be at risk.
“When they first came into Pennsylvania, we had no idea what was going to happen,” says Matthew Helmus. He’s an ecologist at Temple University in Philadelphia, Pa. “They were eating everything. And they were feeding on all these different plants.”
Spotted lanternflies do suck sap from many plants. But few of those plants die, researchers now realize. The critters have a particular appetite for two species. One is the tree of heaven (Ailanthus altissima). An invasive tree native to China, it arrived in the United States in the late 1700s and is now widespread. Its other meal of choice: grapevines.
“If you like wine, if you like grape juice, if you like eating grapes, that’s where I think the impact is going to be,” Helmus says. Large infestations can kill grape plants. So major U.S. grape-growing regions are on high alert for the bugs’ invasion. These regions include western Pennsylvania and the U.S. West Coast.
As spotted lanternflies roam urban sidewalks, people now stomp on them for sport. The plant hoppers are also susceptible to many insecticides. But lanternflies hanging about untreated vegetation can move in when the pesticide wears off.
“Nobody wants to put a lot of pesticides out there,” says Flor Acevedo. She’s an entomologist, or insect biologist, at Penn State in North East, Pa. The toxic chemicals are useful for protecting crops. But they should be applied only where needed because they can harm more than just the pest bug, Acevedo notes. In general, she says, these chemicals are “not good for the environment. They’re not good for other organisms. They’re not good for us.”
Fortunately, research into the spotted lanternfly’s biology and behavior are pointing toward other ways to slow its spread.
Scientists are mapping where these invaders might pop up next. And they’re identifying natural predators and pathogens that could be harnessed to curb the insects’ spread and threat to crops.
Targeting trees of heaven
Tree of heaven and spotted lanternflies are thick as thieves. Controlling one could help control the other.
Spotted lanternfly season officially begins in late spring. That’s when last fall’s eggs begin to hatch. Out come small, black-spotted nymphs. Over the next months, these will feed on sap from more than 70 plant species.
The insects will eventually grow into teenaged forms, called fourth instars. This is when their red stripes appear.
Suddenly, the adults appear. “You’ll see one or two [adults], then all of a sudden you’ll just see them everywhere,” notes Erin McHale. “And they’re hitting you in the head as they’re flying by.” McHale is a biologist at Rutgers University in New Brunswick, N.J.
Winged adults typically emerge in late July and feed voraciously until fall. That’s when they lay eggs. Any surviving adults will die off with the first frost.
Where spotted lanternflies were first detected in Pennsylvania, their preferred food source — tree of heaven — was “just everywhere,” notes Ann Hajek. She’s an entomologist at Cornell University in Ithaca, N.Y. With food so available, “it was really easy for the spotted lanternflies to increase without people even noticing.”
The pests consume sap. Besides tree of heaven and grapevines, they also feed off maple, birch and black walnut trees.
The nymphs don’t like grape plants nearly as well as tree of heaven. Still, they can dine exclusively on grape plants and still reach adulthood. Acevedo and colleagues reported this in the June Environmental Entomology.
Fewer grape-dining nymphs survive to adulthood than do those dining on sap from the tree of heaven. Adults raised solely on grape sap also lay fewer eggs. This suggests culling tree of heavens from areas near vineyards could help protect grapes.
It’s also possible that the trees might serve as bait, luring the sap suckers away from grapes, Acevedo says. Experimental removal of tree of heaven from infested vineyards could help researchers figure out which method — removal or bait — works better.
Other U.S. plants may also prove as attractive to these sap suckers as the tree of heaven and offer as an alternative food source, Acevedo says. “But so far, based on what we see in the field, lanternflies really, really like tree of heaven.”
Tracking spotted lanternfly’s spread
Protecting U.S. grapes will likely become an important, but very tough, task.
The insects haven’t yet invaded major grape regions, such as California or Washington State, Helmus says. But the species “is sort of knocking on the door of the Lake Erie grape belt.” That’s in western Pennsylvania and New York. Without protective action, these sap suckers could become established in California by 2033. Researchers shared this prediction three years ago in Communications Biology.
Spotted lanternflies aren’t migrating slowly. Instead, they’ve been making “random jumps,” Helmus says. “Those random jumps are all driven by the random things that people do.”
Invasive lanternflies often lay eggs on tree trunks. But those eggs also make their way onto trains, cars and shipping pallets. This helps transport the bugs to new places.
Some states, such as New Jersey, have issued quarantines. Businesses there need permits to move equipment and goods. And everyone should inspect cars for hitchhiking lanternflies. But their egg masses, which look like gray smears, can be hard to spot.
“We can see the adults and nymphs quite well,” says Sally Dickinson. She’s an animal behaviorist at Virginia Tech in Blacksburg. “We can go on a crusade to kill all that we can see,” she says. But “that’s probably not going to make a dent in the population.”
Dogs’ powerful noses, however, can help. Trained detection dogs have proven useful for finding spotted lanternfly eggs on farms and at shipping ports. There aren’t enough trained dogs, however, for everywhere they’re needed.
But volunteer dog handlers can also help track down eggs. So pets one day may be recruited to help scout for the insects. Dickinson was part of a team that reported this July 16 in PeerJ. It’s possible that dog-and-human pairs might one day earn a badge or certification to hunt targeted pests, such as spotted lanternflies.
Mapping where these sap suckers are making inroads is another way to tell when protective measures are needed.
One technique uses computers to track bugs, one-by-one. This could help scout for exploding populations. It helps that the spotted lanternfly wing patterns are unique. Researchers reported this February 2023 in Frontiers of Insect Science.
Helmus and his colleagues have tested such “wingerprinting” in the field. They used thousands of photos from around Temple University’s campus to track the insects and estimate their numbers.
Such tracking could help farms and grape growers plan local treatment options. For instance, “if there’s only 200 lanternflies out there,” lots of insecticide might not be needed, Helmus says. “But if there’s 20,000 out there, then that’s a really big deal.”
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Finding lanternfly predators and pathogens
Invasive species typically benefit from a lack of predators. And that’s true for spotted lanternflies in the United States. But that may be changing.
Birds have been reported chowing down on the insects. So have some predatory arthropods, including spined soldier bugs.
Bats have been sampling them, too.
McHale, from Rutgers, initially thought that lanternflies were mostly active by day. But she stumbled onto something interesting while working on a project with bats. As her team returned home from the field at three or four in the morning, they saw lanternflies climbing up and down building walls.
That got McHale wondering: “How cool would it be to show that bats are now incorporating these guys into their diet?”
To investigate in New Jersey, her team extracted genetic material from the guano of big brown bats and eastern red bats. Both are consuming spotted lanternflies, they now confirm. They shared this finding last February in Forests. It suggests bats might help reduce lanternfly numbers.
Analyzing bat guano could also become one way to scout for the insects in areas where they have not yet been seen.
In the spotted lanternfly’s native China, a fellow predator is on the prowl. It’s a parasitic wasp (Anastatus orientalis) that lays its eggs inside those of spotted lanternflies. The wasps’ eggs prevent lanternfly eggs from hatching.
That wasp may have helped control local spotted lanternfly populations after the invasive insect swept through South Korea in 2004.
Wasps might help in the United States, too. But researchers need to find ones that kill spotted lanternflies without too many native casualties, says Mari West. She’s an entomologist at the University of California, Riverside. She also works with the U.S. Department of Agriculture (USDA).
Among the most promising wasps: Dryinus sinicus. This China native lays its eggs inside nymphs. USDA researchers are currently testing whether it has any interest in native U.S. plant hoppers, West says.
Also under consideration is A. reduvii. This wasp can be found across North America. It attacks lanternfly eggs at high rates. West and her colleagues shared this find in January in Biological Control. Because this wasp is “already native here,” West says, “we might expect less of an impact to our native plant hopper or other insect species.”
It’s not just hungry animals that have put lanternflies in their crosshairs.
In October 2018, Hajek, from Cornell, was part of a team that found dead adult lanternflies under or attached to trees in a wooded area near an apple orchard in Reading, Pa. Two common fungal pathogens — Batkoa major and Beauveria bassiana — had caused a mass die-off.
Both fungi dwell in soils across the United States. That makes them an attractive living “insecticide,” Hajek says. “It’s not like a synthetic chemical insecticide that can have an unwanted impact on lots more things in the environment and humans.”
Many other fungi also infect spotted lanternflies. It’s unclear, however, whether they actually kill the insects.
B. bassiana coats insect bodies in a white fuzz. It’s already commercially available to control other pests (such as thrips and aphids). In field tests at a Pennsylvania park, the fungus killed nearly half of lanternfly adults and fourth-instar nymphs. Hajek and her team reported this back in 2020. When the fungi were applied directly to adults, more than nine in every 10 of the infected insects died after nine days hanging out on potted grapes.
The other fungus, B. major, is hard to mass produce. But if researchers succeed, it could cause lanternflies a lot of hurt. This fungus sends the sap suckers it infects climbing up trees or other vertical surfaces. There, fungal tendrils anchor these victims to a surface, killing the insects and shooting off spores.
During the 2018 outbreak, B. major “caused a whole lot of infection in the spotted lanternfly population and basically took out the population,” Hajek says. “That’s pretty exciting.”