Since 2007, roughly 8 million of these wasps have been released every year around the country, said Nicole Sawallich, acting entomologist and supervisor of the USDA EAB control program.
In that time, they’ve shown early signs of controlling an EAB invasion that has swept across the country, with Michigan as its epicenter.
Ash trees were once one of the most abundant trees in Michigan, but in just two decades they’ve become endangered, impacting Michigan’s ecology, economy and Indigenous culture.
Ash trees are crucial for basket weaving in native tribes, and wood from ash trees is commonly used in furniture, timber, even baseball bats. Ash forests provide habitat for many species, and the trees’ fallen leaves help nourish other plants, said Deborah McCullough, a Michigan State University professor in the departments of entomology and forestry.
“Keeping those forests diverse with some of these natural species” allows the native ecosystem to continue, said James Wieferich, forest health unit manager at the Michigan Department of Natural Resources.
What makes EAB so destructive
A deceptively beautiful metallic green-winged beetle, female EAB lay eggs under the bark or in cracks of ash trees.
Within a few weeks, the larvae chew S-shape patterns, or galleries, through the bark toward the phloem, a tissue in the inner bark that transports nutrients between the leaves and roots. The larvae continue to feed into the xylem, a further inner tissue that carries water from roots up to the leaves.
As the larvae multiply they cut the tree’s ability to transport nutrients, its canopy grows thin, ultimately leading to the tree’s death, McCullough said.