WHAT HAPPENED TO LANTERNFLIES?
Fewer of the invasive pests are being reported in the region, but researchers aren’t yet sure exactly what’s going on
Where have all the spotted lanternflies gone?
That was the question it seemed everyone kept asking Manatawny Winery owner Darvin Levengood this week at the Oley Fair. His battle with the invasive Asian planthopper is well-known. Back in 2018 and 2019, he lost a few acres of prized vines that he has yet to replace. Spotted lanternflies don't eat grapes, he's found. They prefer the sap in vines, which over a few years stresses and damages each vine until it eventually dies.
Last year, he saw fewer lanternflies in the vineyards, probably due to the weather, but all best guesses were that the population would rebound this year.
“It didn't happen,” Levengood said. “We're seeing fewer lanternflies than 2020. That is a real puzzle. We're scratching our heads saying, ‘Where the heck are the lanternflies?'”
“We just started picking grapes a few days ago. Pickers would be bombarded with them, but this year you've had to search for them.
“Quite frankly it's a bloody mystery.”
If you have noticed fewer spotted lanternflies you aren't alone.
Shannon Powers, press secretary for the Pennsylvania Department of Agriculture, said the pests are definitely on the move but that it remains to be seen whether they are on the decline. Reports are down, but that does not mean they are gone, she said.
“Our field inspectors and USDA teams in Southeast PA are definitely seeing fewer spotted lanternflies this year,” Powers said. “It may be partially due to public and private efforts to control the insect, or just the natural movement of the pests to new areas. Scientists are not really sure.”
Spotted lanternflies don't live more than a year, and they can't fly. That means something disrupted their life cycle preventing
“Reports are not necessarily an indication of population levels in an area. In areas like Berks County that have seen infestations now for several seasons, decreased reports are sometimes due to ‘reporting fatigue,’ or people just not seeing the point of continuing to report new insect populations.”
— Shannon Powers, press secretary for the Pennsylvania Department of Agriculture
the next generation in a certain area. Scientists have a few theories. They say that most likely it’s a combination of factors: weather conditions, host plant availability and predators.
“It would be great to figure specifics and use it to predict populations of the future — to protect vineyards,” said Emelie Swackhamer, a Penn State extension educator based in Montgomery County.
Food
It may be that they’ve exhausted their food source. They prefer the invasive tree of heaven (ailanthus altissima), and there have been aggressive efforts to remove those trees. But if tree of heaven grows back, would the lanternflies return?
“The jury is out on whether this is going to be a long term thing in what we call the core area (Berks),” said researcher Kelli Hoover, a professor of entomology at Penn State. “They move so much it’s hard to know whether they moved out of the area because they exhausted what is available.”
Hoover noted, however, that in the absence of tree of heaven they will feed on other trees — especially maples — and grape vines. And scientists have yet to pinpoint what it is about the tree of heaven that is so beneficial to spotted lanternflies. Unlocking that mystery might help disrupt the spread.
There is research underway to understand the level of feeding pressure on trees and what it takes from spotted lanternflies to trigger a carbohydrate decline that leads to the death of the tree.
Hoover said there is also research underway for the nursery industry to understand how much tree growth is slowed by the insects.
Predators
Another possibility for the fewer spotted lanternflies is that there are predators. Some research is beginning to show that birds and bugs such as spiders will eat the pests. It seems that these native predators prefer the lanternflies that have not fed on the tree of heaven. But Hoover noted that spiders have no preference.
“I think we may be seeing local predators taking advantage of a new food source,” Hoover said.
Weather
The weather may have also been a factor. Dryer winter winds can reduce the success rate of lanternfly eggs hatching, Swackhamer said. But no one expects weather to wipe out the insects, as the lanternflies have survived the Polar Vortex, Swackhamer noted.
A lot of rain and moisture in the fall of 2018 may have allowed fungi to flourish that killed some lanternflies. There has been research that shows Batkoa major and Beauveria bassiana do kill the insect. There may be others.
The insect is ahead of researchers who have to plan and execute experiments annually.
Cycles and corridors
Swackhamer said that researchers are beginning to see population cycles that are localized and different from year to year, similar to gypsy moths.
“We’re definitely in a long haul situation with this,” she said. “We’re learning in Berks County how to minimize impact on our grape production and our quality of life. I think other areas are getting into that too.”
Public reports of lanternflies have decreased in previously infested areas even as they ramp up in new areas of the state like Harrisburg. Public reports often misidentify the insects, particularly in areas outside the quarantine, but reports tend to be highly accurate in areas where the insect has been established longer.
Data from these reports is what scientists and specialists use to predict patterns of spread and assess whether or not the quarantine should be expanded to a new area. Inspectors follow up on every confirmed report outside the quarantined area to establish whether or not it’s an isolated insect that has “hitchhiked” there or an established infestation. They then treat areas as appropriate, she said.
From Jan. 1 to Sept. 7, the department received 151 public reports of lanternflies in Berks County and 21,706 reports statewide. For all of 2020, there were 955 reports from Berks County and 82,884 reports statewide.
“Reports are not necessarily an indication of population levels in an area,” Powers said in an email. “In areas like Berks County that have seen infestations now for several seasons, decreased reports are sometimes due to ‘reporting fatigue,’ or people just not seeing the point of continuing to report new insect populations.”
The state has shifted its spotted lanternfly mitigation efforts to transportation corridors where ‘hitchhiking’ bugs are most likely to escape the quarantine zone. Spotted lanternflies don’t fly but are oriented to climb high, and with a hop they can flutter to new areas. Tucked into cars, trucks and shipping containers, they have managed to travel outside of Berks, the place where they were first discovered in a shipment of stone in 2014.
“I’m in total agreement with the Department of Agriculture really going after the transportation corridors because that is where the spread is happening,” Hoover said.
Powers said it is still important to report new populations but even more important to “look before you leave,” and inspect your vehicle and cargo to prevent taking insects to a new home when you travel.
The spotted lanternflies will start laying eggs soon. Already there are reports of egg masses being found in New Jersey. People are still advised to squash the bugs they say and scrape egg masses when possible.
Swakhamer said the overall strategy with the insects has not changed, including getting rid of the tree of heaven.
Officials advise people not to move firewood. Check your vehicle when leaving the quarantine zone. Business owners should be sure their permit and training is up to date.