Karen Gray has seen hundreds of spotted lanternflies descend on her patio and says killing them is like playing “whack-a-mole.”

Maureen DePasquale has begun hunting them with a salt gun. And Mike Rossmark now drags a vacuum into the woods behind his house to suck the critters to their doom en masse.

These Cherry Hill residents are experiencing a full invasion of the pest from Asia that first appeared in the United States in Berks County, Pennsylvania, in 2014. The invasive insect has already swept through 21 counties in Pennsylvania.

This year, the spotted lanternfly seems to have fully established itself in densely populated South Jersey counties like Camden, Gloucester and Burlington.

The first season of eggs, laid in fall and hatched in spring, are now wildly colorful adults hopping from tree to tree.

The insect, though not harmful to humans or pets, can harm plants as it feeds on the sap of trees such as maple and black walnut.

During feeding, as it pierces plant tissue, the spotted lanternfly excretes a sugary substance known as honeydew that attracts bees and other insects. The honeydew promotes the growth of mold that stresses and damages plants.

The pest strongly prefers the invasive — and now nearly ubiquitous — tree of heaven.

Its main threat, though, is to agriculture, particularly cultivated grapes in commercial vineyards.

Agents with Rutgers’ New Jersey Agricultural Experiment Station began reporting a “dramatic increase” in the pests’ presence on farms last year.

George Hamilton, chairman of Rutgers’ department of entomology, said damage so far this year has been minimal, but added: “That may change.”

Anne Nielsen, an associate professor in the entomology department, said she’s getting reports of larger numbers this year, increasingly in central and South Jersey.

The New Jersey Department of Agriculture lists eight counties as under quarantine: Burlington, Camden, Gloucester, Hunterdon, Mercer, Salem, Somerset and Warren. However, Nielsen says the pests are present in more than half the state’s 21 counties.

“We are still in the expansion and growth phase for this invasive bug and management needs to be implemented immediately,” she said.

The pest also poses a threat to apple, cherry, and peach orchards. Some growers have started to apply insecticides against nymphs. Though the pest has caused vineyard losses in Pennsylvania, it is not yet known if it has done so in New Jersey.

The insects pose the biggest threats in mid-September when they are most likely to feed on shoots.

Lauren Bonus, an entomologist for the Camden County Mosquito Commission, said the county is just starting to grapple with how to control the spread in residential areas. She said adults that arrived last year laid eggs that hatched this year in sacs containing about 30 to 50 eggs each.

“I would say that there are more now due to a lack of control,” Bonus said. “They are an invasive insect without a predator. We tell people the best thing you can do is kill them.”

Bonus said the county began putting up bands of sticky tape around trees in sections of Cooper River and Newton Lake Parks.

For nymphs and adults, nonchemical sticky bands are the most effective traps available, according to Penn State Extension, part of the university’s College of Agricultural Sciences. The bands are designed to be wrapped around trees about 4 feet off the ground to trap nymphs and adults crawling up the trunks to feed. But they should be installed only on trees where spotted lanternflies have been sighted because they can capture other critters, such as bees and butterflies.

Though it’s too late this year, egg masses can be scraped off tree trunks in the spring, double bagged, and tossed away, with the option of placing the eggs in alcohol, bleach or hand sanitizer first.

Many homeowners have devised their own methods of killing the pests, using household soap solutions and other homemade concoctions. Store-bought solutions include DePasquale’s salt gun bought on Amazon that blasts the bugs with table salt, which users say eradicates them. She and scores of other Cherry Hill residents shared their experiences on an Inquirer post on a local Facebook group, where Carol Topham Rachfalski reported seeing the nymphs on her backyard grapevine.

Penn State Extension, which has become a go-to source on spotted lanternfly information, has online instructions for how homeowners can manage the pests through traps, pesticides and other methods.

In New Jersey, Rutgers asks that residents report sightings and locations with a photograph, to slanternfly@njaes.rutgers.edu.

Farmers, nursery workers, and vineyardists can report sightings to SLF-plantindustry@ag.nj.gov.

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