An all-female wasp is rapidly spreading across North America’s elms

She’s little than a centimeter long, produces only daughters and is conquering nan continent without a azygous male. Meet nan elm zigzag sawfly, named for nan delicate zigzag patterns it carves into elm character leaves.

Despite its name, nan elm zigzag sawfly (Aproceros leucopoda) is not a fly; it is simply a type of wasp first discovered successful North America successful 2020. Originally from East Asia, it has expanded its scope astatine an “alarming” rate, researchers study successful nan Journal of Integrated Pest Management. For cities still recovering from elm canopies mislaid to a fungal disease, it’s an unwelcome 2nd activity of assault. And recently emerging grounds suggests it won’t extremity astatine elms.

In conscionable complete 5 years, nan (seed) disease has dispersed to 15 U.S. states, from New Hampshire to Minnesota and southbound to North Carolina, says Kelly Oten, an entomologist astatine North Carolina State University successful Raleigh. “We conscionable had to adhd Indiana,” says Oten, who maintains a representation of elm zigzag sawfly sightings.

Freshly hatched elm zigzag sawflies trim zigzagging lines into leaves. “The feeding shape is oddly cute,” Oten says. But arsenic nan larvae mature, they tin portion capable foliage from a character to time off it almost bare.

The larvae of elm zigzag sawflies chew retired a signature zigzag shape into leaves, specified arsenic nan American elm leafage shown here.Kelly Oten

To spot if nan wasp would onslaught trees beyond elms, Oten’s squad planted Japanese zelkova (Zelkova serrata) adjacent an infestation tract successful Ohio. Many U.S. cities person started planting zelkovas, an elm relative, since they look resistant to Dutch elm disease, nan fungal affliction that has killed tens of millions of American elms successful nan past century.

The researchers observed nan wasp laying eggs, feeding, pupating and emerging arsenic adults connected zelkova saplings, which nutrient caller leaves earlier than elms successful nan spring. As nan play progressed, nan wasp switched backmost to elms, suggesting that zelkova whitethorn service arsenic an alternate big erstwhile elm foliage isn’t available, nan researchers say.

The uncovering amazed Véronique Martel, a wood entomologist pinch Natural Resources Canada who reported North America’s first elm zigzag sawfly discovery successful nan state of Quebec successful 2020. “It is uncommon that insects tin move hosts,” she says. Martel, who wasn’t progressive successful nan study, suspects that being capable to provender connected zelkovas could make nan wasps moreover much successful, by allowing them to commencement multiplying earlier successful nan year. “They tin make a batch of generations wrong a summer,” she says.

A important driver down nan zigzag sawfly’s accelerated dispersed is an different reproductive strategy called thelytokous parthenogenesis, successful which females laic unfertilized eggs that nutrient only much females. This intends that moreover a azygous ovum hitching a thrust connected firewood aliases a car tin commencement a caller infestation. No males person ever been found.

For reasons researchers don’t yet understand, nan zigzag sawfly larvae trim only insignificant zigzag patterns successful immoderate elms while severely defoliating elms successful different areas. “At this point, we do not cognize if it’ll termination nan character aliases conscionable accent it greatly,” Oten says.

Unwitting quality accomplices person astir apt aided nan sawfly’s accelerated spread. Oten’s squad documented cocoons pinch elm zigzag sawfly pupae clinging to motortruck mirrors and instrumentality wells, which tin transportation nan insect acold beyond its earthy dispersal scope of 45 to 90 kilometers annually. Researchers deliberation nan (seed) disease whitethorn person arrived successful North America hidden successful nan ungraded of a houseplant.

With elms autochthonal crossed astir of nan eastbound United States and Canada, elm zigzag sawflies person a immense territory available. “I do deliberation we will person galore much reports successful further counties and apt much states” successful 2026, Oten says. Temperature extremes whitethorn yet limit nan insect’s range, she notes. “But arsenic of correct now, it’s North Carolina to Canada. That’s beautiful wide.”

Oten is testing pesticides to thief homeowners protect their trees. Early tests of 2 soil-applied insecticides show promise, and she expects to people nan afloat results wrong months. For now, she recommends checking vehicles for cocoons earlier leaving infested areas and reporting zigzag patterns to section hold offices.