Elm wasp marks on leaves
The elm wasp is decimating elm trees in the United States. Its form of reproduction, which does not require a male, is also contributing to its rapid expansion.
An invasive species of insect known as elm wasp is spreading rapidly across North America, raising concerns among scientists and forestry officials about the health of elms.
First detected on the continent in 2020, the species has now been confirmed in 15 North American states and four Canadian provinces, according to new research in the Journal of Integrated Pest Management.
Its larvae are easily recognized by characteristic zigzag pattern that they leave on the elm leaves. While the damage may seem small at first, severe infestations can defoliate trees down to the veins, weakening them over time and increasing their vulnerability to drought, disease and other stressors.
“Repeated defoliation over several years can significantly reduce tree health and growth,” he said. Kelly Otenentomologist at North Carolina State University and lead author of the study.
The insect’s rapid expansion is driven by two main advantages. The first factor is your ability to feed on more than one species of tree. In addition to the elm, researchers confirmed that the sawfly can also feed on the Japanese zelkova, a tree very common in urban areas. This host switching behavior is uncommon among insects and allows the species to explore food sources that may appear earlier in the season, enabling the development of multiple generations in a single summer.
The second factor, and the most worrying, is the sawfly’s method of reproduction. The species reproduces through a process known as thelitochic parthenogenesis, which means that females can lay unfertilized eggs that hatch into genetically identical females. No males have been identified in North America. As a result, only a single insect can establish a new population, explains .
Researchers have found evidence that human activity is accelerating the spread. were discovered cocoons attached to vehicles and construction materials, allowing insects to travel far beyond their natural dispersal range, up to 90 kilometers per year.
With the elm native to much of eastern North America, scientists expect the wasp’s range continue to expand. “We are likely to see many more reports in other states and provinces,” Oten said.
Currently, there is no widely recommended control method. Researchers are testing pesticides to determine their effectiveness, but the results have not yet been released. For now, experts recommend that the public and forestry workers remain vigilant.
