This week we take a respite from periodical cicadas we have visited during the past several weeks and return to a story of our sorry ash trees. Back in the first week of May we visited mighty ash trees on the banks of the Potomac devastated by the lethal Emerald Ash Borer. But in the great circle of life, havoc wrought by one creature becomes a bounty for others. Ash trees dying at the jaws of Emerald Ash Borer larvae become magnets for other creatures that feast on both the pest and its victim, the ash tree. In the previous episode we witnessed “blonding” of ash trees, the telltale handiwork of woodpeckers searching for nutritious larvae of Emerald Ash Borer. A recent study of Emerald Ash Borers in Maryland’s ash forests revealed legions of woodpeckers as the primary source of mortality for the deadly reapers of ash. Cleary, the invasion of our forests by Emerald Ash Borer has proven a bounty for these feathered reptiles.
Once EAB beetles have plunged the ash into a death spiral, the nutrient rich tissue of the dying ash serves as an important food source for many other species of insects. On a return visit to the ash killing fields along the Potomac, I was amazed to find hordes of Banded Ash Borers swarming over the surface of fallen trees. Unlike the exotic Emerald Ash Borer that attacks healthy trees, Banded Ash Borers are native to the forests of North America where they attack stressed and dying ash, hickory, elm, and oak. In spring beetles can be found navigating the bark of dying trees. Their striking pattern of white and yellow bars set against a dark background provides an illusion of wasps dashing about. This, no doubt, is a visual display to deceive predators that might want to make a meal of a tasty beetle, but would avoid a meal of a fierce stinging wasp.
Like other species of insects we met in previous episodes including mason bees, wheel bugs, Hercules beetles, lovebugs, periodical cicadas, dogbane leaf beetles, and milkweed longhorned beetles, males that successfully win a mate often guard them for extended periods of time to ensure their sperm, rather than sperm of a subsequent suitor, fertilize the female’s eggs. I was surprised to see female Banded Ash Borers dashing about busily inserting eggs into fissures in the bark, seemingly oblivious to obstreperous males riding on their backs.
Watch as a male Banded Ash Borer beetle scrambles to keep possession of his mate while Ms. Nonchalant goes about the important business of inserting eggs into fissure in the bark of a fallen ash tree.
Eggs deposited into bark fissures hatch, and the tiny legless larvae emerge and go in search of food. The larvae use powerful jaws to bore through the bark and eventually drill deeper into the sapwood, consuming nutritious tissue along the way. Banded Ash Borer larvae go by the name of roundheaded borers by virtue of the fact that in cross-section their front end is more or less round. This contrasts with larvae of the Emerald Ash Borer, whose front end in cross-section is compressed from top to bottom thus giving them the common name of flatheaded borers. After feeding during spring, summer, and fall, the Banded Ash Borer larvae complete larval development and pupate in a chamber beneath the bark. Most juveniles complete development in a single year and emerge the following spring to find recently dead or dying trees that will serve as food for their young. The demise of our ash forests brings good fortune to some predators like woodpeckers and recyclers like Banded Ash Borers. Unfortunately, though, the toll on overall biodiversity in these killing fields of ash is enormous.
The fascinating paper “Quantifying the impact of woodpecker predation on population dynamics of the Emerald Ash borer (Agrilus planipennis)” by D. E. Jennings, J. R. Gould, J. D. Vandenberg, J. J. Duan, and P. M. Shrewsbury, and the article “Banded ash borers” by Theresa A. Dellinger and Eric Day were used to prepare this episode.
To learn more about Banded Ash Borer please visit the following website: https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ENTO-133/ENTO-133-PDF.pdf