(WGHP) — North Carolina researchers are tracking the state’s newest invasive species: the elm zigzag sawfly.
Native to East Asia, the elm zigzag sawfly was first discovered in the United States in 2021 and has been spotted in five Eastern states, including North Carolina, according to Kelly Oten, assistant professor and extension specialist with N.C. State University’s forest health resource.
Elm zigzag sawflies were found in Europe around 20 years ago, but researchers aren’t sure how they got to the U.S.
The invasive insect was first detected in North Carolina in August 2022 in Stokes and Surry counties when a North Carolina Forest Service assistant ranger found one in Westfield, north of Pilot Mountain, after being contacted by a homeowner.
They are a type of wasp named for a saw-shaped appendage they use when laying eggs and for the zigzag pattern left behind on leaves after they feed.
Elm zigzag sawfly feeding pattern (credit: Dr. Kelly Oten, assistant professor and extension specialist, forest health) 
NC has new invasive species found in Surry, Stokes Counties (credit: NC Department of Agriculture and Consumer Services) 
NC has new invasive species found in Surry, Stokes Counties (credit: NC Department of Agriculture and Consumer Services)
They cannot sting and are harmless to people and animals, but, as the name suggests, the elm zigzag sawfly can cause significant damage to elm trees since they can increase their population size quickly, according to Brian Heath, an NCFS forest health specialist.
Elm zigzag sawfly females reproduce without mating, so they can have multiple generations every year. North Carolina’s sawflies are on their third generation of the year, Oten says.
A single generation lasts about a month, and the first North Carolina generation of 2023 emerged in the spring.
Insect “development goes faster where it’s warmer, and we’re … the most southern latitude of this insect right now. Everyone else who has it is north of us, so we saw it emerge first [in 2023], and we’re probably going to see it overwinter last, which means they’re feeding longer here, and potentially doing more and more damage,” Oten said.
Impact
Forest health experts are still working to determine what the long-term impact of the invasive species will be in North Carolina.
“This is when we see the worst damage from this insect. Even though they come out in the spring and they start feeding, that feeding isn’t very noticeable at first. … As the populations are growing, they’re removing more and more leaves, and it’s more obvious on the trees,” Oten said.
Oten says researchers are concerned about elm zigzag sawflies feeding on multiple trees in the elm family, but it is currently too early to tell how much damage the insects will do in North Carolina since forest health workers have only been able to observe the insect for one year.
Pesticide trials are underway.
“It is looking good. It looks like we’re going to have promising options for landowners soon or homeowners for those trees in their front yard,” Oten said.
Oten and other researchers have also partnered with the USFS to try and learn where exactly elm zigzag sawflies are in North Carolina and will start a three-year project in January to learn as much as they can about the invasive insects.
“We suspect it’s in a lot more areas than we know about because a lot of the damage that it does is not noticeable,” Oten said. “We’re trying to see how bad this is going to be. … We’re telling people not to freak out, but that’s based on the fact that it’s a defoliator, and typically defoliators don’t kill trees, but if it happens year after year after year then it can really stress and weaken trees, and in some cases, it does kill trees.”
What to do
The elm zigzag sawfly is a “quarantine pest,” which means every time it is detected in a new county, the United States Department of Agriculture has to confirm the report, according to Dr. Oten.
“If you see a defoliating elm tree that you suspect is being impacted by this new invasive pest, note the location, try to safely photograph the insect and the leaves that have been eaten upon and contact your local NCFS county ranger,” Agriculture Commissioner Steve Troxler said. “As North Carolina’s list of invasive species gets a little longer, you can help us keep our forests healthy and thriving by reporting these bad bugs.”
People who suspect there is an infested tree in an area near them should contact their NCFS county ranger. Visit the N.C. Forest Service website to find contact information for your county range.
