Nature Nearby: Green invaders in Magruder Park

BY FRED SEITZ — Walk along the bike path near the Northwest Branch and you may notice signs about a research project at the edge of the woods. On a mild winter day, I saw a team of entomologists from the University of Maryland (UMD), one of whom told me that they were working on a project to control emerald ash borers in the area.

The emerald ash borer, which is native to temperate regions of Asia, is an invasive beetle about one-third of an inch long. In its adult stage, the borer is bright green. In the U.S., emerald ash borers were first detected in Michigan in 2002. Scientists believe that they hitchhiked here in packing crates, possibly from China, in the early 1990s.  

Ash borers have complex life cycles. Long-living females can deposit up to 200 eggs in cracks and crevices of ash trees, preferring trees that are stressed or weakened. During their development within the tree, the larvae eat inner bark, which compromises even healthy trees. The borers develop within the tree over one to two years, and finally emerge as adults and feed for about a week on the tree’s leaves before mating. Their emergence from trees is usually indicated by small D-shaped holes. When I spoke with the UMD entomologist, she showed me some pupae they had removed from crevices in a couple of ash trees near the bike path. The pupae were small yellow beasties, quite different in appearance from the adults.

Ash borers infest various species of ash trees and have killed millions of trees from southern Canada to the southeast U.S and as far west as Colorado. The cost of this destruction has been estimated in the billions of dollars. In their host countries, ash borers are not as destructive because they have native predators. In North America, however, their infestations have led to prohibitions against moving firewood and using pesticides. Natural predators, including varieties of wasps and some types of fungi, have been introduced and are controlling ash borers to a limited extent. Additionally, some jurisdictions have removed infested ash trees to prevent the borers from spreading to other trees. Ash borers may travel as far as 12 miles from where they hatch.

Both the U.S. and Maryland Departments of Agriculture monitor the presence and spread of ash borers. The purple traps often seen in Maryland trees in spring and summer are part of this monitoring effort.

If you identify ash borers, or think that you have, please notify the Maryland Department of Agriculture; the agency’s Washington Metropolitan contact number is 301.261.8106. The ash trees will thank you for it.