A year ago, researchers expressed optimism about the possible eradication of the spotted lanternfly. Their optimism was not echoed at the 2016 Mid-Atlantic Fruit and Vegetable Conference.
“USDA and the Pennsylvania Department of Agriculture are doing their best,” Penn State University entomology professor Mike Saunders said at the February conference in Hershey, Pennsylvania. “But I don’t think eradication is possible anymore.”
Movement of egg masses is the determining factor. First detected in 2014 in eastern Berks County, Pennsylvania, the pest entered the United States by means of egg masses attached to landscaping stone imported from South Korea.
The gray egg masses were easy to miss on the gray-colored stone, and it’s the movement of egg masses by human means that is the root of Saunders’ skepticism.
“That’s how the gypsy moth spread throughout the Eastern United States,” he said. “Families with camping trailers might have had egg masses attached to them. They’d overwinter and spread to another area where they’d hatch in the following season.”
As of Nov. 15, 2015, the Pennsylvania Department of Agriculture listed four southeastern Pennsylvania counties — Berks, Bucks, Chester and Montgomery — as part of its spotted lanternfly quarantine area.
Fear of the unknown
Spotted lanternfly is unlike gypsy moth in one crucial way. “I don’t anticipate difficulty in controlling them,” Saunders said. “There are a number of systemic and contact pesticides that should do that.”
Because it is a new species in this part of the world, however, it has few natural enemies. The assassin bug is one, but appears to have a limited impact. Saunders said he sees a lot of intact dead lanternfly insects on the ground months after they died.
Concern about the pest is grounded in what U.S. entomologists don’t know about the insect. The first information they found came from a 2006 Korean document telling of damage to “grape orchards” there, though they have yet to determine the infestation’s scale or range.
There is also no known research on how the insect impacts grapevine growth, health and yield. “We’ve not seen any direct statement in the literature on how they damage grapevines,” he said.
Saunders and his graduate student, Erica Smyers, have supplemented the Korean data with a good deal of information gathered from the field.
The lanternfly’s mouth parts are designed for piercing and sucking. It penetrates the bark, taking soluble nutrients from the phloem, the layer that moves water, sap and nutrients through plants and trees.
Another question entomologists have is whether the feeding site injury becomes a wound through which another disease or insect might enter the plant.
As the insects feed, they retain the proteins they want and rid themselves of the sugars and carbohydrates they don’t want. In doing so, they excrete a thick white residue called “honeydew” in large quantities.
It is possible honeydew damages plants as much as the insects do. For example, the honeydew might act as a fungal mat, a substrate for molds to grow or form a nutrient layer for pathogens to mature and take hold of the portion of the plant it covers.
Scientists have determined from the Korean data the number of degree days it takes for larvae to hatch, what the lethal winter temperatures are for the pest and that the female spotted lanternfly deposits its egg mass on flat surfaces.
Egg masses hatch in May.
Host plants include fruit trees, ornamentals and hardwoods. “Their preferred host plants appears to be tree of heaven,” said Saunders.
There are four nymphal stages called instars. In stages one and two, the instar is black with white spots. In stages three and four, it acquires a red warning color with white patches.
The fourth instar nymphal spotted lanternfly molts to become a 1-inch long and half-inch wide, winged, sexually mature moth.
Its front wings feature a red color along the edges and black blocks surrounded in gray toward the tips; back wings are tipped with black with a white band in the middle and a red and black spotted section at the bottom.
Good news for growers is early instars do not appear to damage grapevines. More good news: there is only one generation per year.
“That means, assuming that our observations of their weak flying ability implies only modest mobility during the growing season, if you knock them down once in the season, you may not have to make another application to control them a second time in the same year,” Saunders said.
Despite having wings, the adult spotted lanternfly is not very mobile. To date, very few have been observed moving from surrounding forests into vineyards.
Once developed, a good integrated pest management program will determine if a vineyard has an infestation, as well as the age and size of the infestation and timely applications to control it, including whether it would be profitable to control younger populations.
Saunders and Smyers are working to develop an effective integrated management program for this pest, a major emphasis of their research.
In an attempt to determine its threat to the grape industry, Saunders and Smyers collected egg masses in April and in October and November. Returning to Penn State, they put them into a quarantine room, storing them in a refrigerator with temperatures between 5° and 7° Celsius (41° and 45° Fahrenheit).
Later, the chilled egg masses were placed in rearing cages at room temperature.
It took an average of 18.7 days for the masses to hatch. Once hatched, they transferred the nymphs to rearing cages containing live grapevine roots and recorded hatched versus unhatched numbers after emergence.
Their most interesting finding: Most nymphs did not survive past the third instar. Whether that was due to nutrition, disease, grape variety or fertilizer, they just don’t know.
The second study is in progress. Saunders said they have established a small vineyard inside the quarantine zone so they might assess adult feeding impacts in terms of quantity, grapes and grapevines.
Next year, Saunders and Smyers plan to introduce spotted lanternflies onto the vines, which are enclosed in cages to prevent the insects’ spread, to observe the impacts outside of laboratory conditions.
State of readiness
If Saunders is correct and spotted lanternfly eradication is not possible, Eastern growers should be alert for possible infestations. In addition, if human transport of egg masses is indeed a factor, this problem may not remain limited to the immediate area of southeastern Pennsylvania.
Growers who have tree of heaven stands may want to keep a watchful eye in their vineyards and on those trees for insects, honeydew or egg masses.
“If you see egg masses,” said Saunders, “scrape them off the tree or smooth surface and place them in a tightly sealed container with 70 percent alcohol or hand sanitizer to kill them.” •
– by Dave Weinstock