The Emerald Ash Borer Took More Than Shade

Essay by:  Dr. Erwin (Duke) Elsner; Small Fruit/Consumer Horticulture Educator

Michigan State University Extension

Emerald Ash Borer (Pennsylvania Department of Conservation and Natural Resources)
Emerald Ash Borer (source: Pennsylvania Department of Conservation and Natural Resources)

Most people who appreciate the natural resources of Northern Michigan are aware of the unnatural changes underway in our forests. Over the last 15 years or so, we’ve watched as most of the ash trees have succumbed to attacks by the Emerald Ash Borer. Representing 15% or more of all trees in the forests of our region, this is a big loss. We’ll miss those compound leaves turning dark green in the summer and shade. But there’s much more to an ash tree than the comforting shade.

In most settings, mature trees support a 100 insect species or more. When trees age and die or are felled by a storm, the losses are interspersed and not confined to one species. The mix of species and age diversity of trees in a healthy forest give insects many options. But when most or all of a single species dies, specialized insects and animals suffer.

Having focused most of my research and professional life on entomology, I’ve developed a deep appreciation for insects and the roles they play in healthy ecosystems. And for decades now, I’ve enjoyed studying and collecting moths and butterflies – Lepidoptera. Beautiful, showy and engaging, these creatures are important pollinators and key food sources for birds, bats, frogs and other animals.

great ash sphinx mounted cropped
The Great Ash Sphinx Moth

So, when the ash trees began dying, and it became clear that almost all of these trees would die, I thought of some very special caterpillars and moths, particularly the Great Ash Sphinx moth (Sphinx chersis). With a wing span of 4 to 5 inches, colored dark gray or blue-gray with black dashes on the wings, this moth is a real eye-catcher. This big, popular, showy moth was once common in our area – thanks to an abundance of ash trees, the caterpillar’s primary source of food.

In the caterpillar or larva stage, the Great Ash Sphinx is also quite big; it is the same size and shape as a tomato hornworm. In the caterpillar stage, this moth represents a very valuable food source for birds during the nesting season. However, without the ash tree, these insects are becoming hard to find in Northern Michigan. Trees, insects, birds . . . they’re all connected.

So, what can we do? We could make a bigger effort to fight off the Emerald Ash Borer, but the best way to do that is with systemic insecticides. Unfortunately, using systemic insecticides would kill many other insects that feed on the ash trees – helpful and harmful. There may be a way to respond with biological controls. Scientists at Michigan State University and the Chinese Academy of Forestry began working to identify natural enemies of the Emerald Ash Borer in 2002. These researchers are working with the borer’s natural enemies form Asia, including parasitic wasps, but the results and application of that research will be too late to save our region’s ash trees.

Great Ash Sphinx Larva
Great Ash Sphinx Larva

We may be able to find and plant varieties of ash that are resistant to the Emerald Ash Borer. That is an important consideration for the future of this tree species and, maybe, many others.

As invasive species of plants and insects gain a foothold in the region and our climate warms expanding the frost free season, we will be confronted with more of these challenges. We need to ask and answer a lot of questions – region wide, as a community. Will we plant new trees to replace the ash we’ve lost and are losing? What species of trees can we nurture in our changing climate to help maintain the diversity of insects and animals that so enrich our region? If we lose a lot of birds, how will we deal with the resulting explosion in nuisance insects?

These are important and ever more pressing questions. In the last few years, we have heard that our region’s beech trees are now in trouble. Another invasive pest and a related fungus have begun to infect and kill most of the beech – a very significant part of our forested landscape. Once again, the whole web of life shakes.  Many forest animals feed on beech nuts and many dozens of insect species feed on the leaves and branches. In turn, these insects support many predator species.

The Early Hairstreak Butterfly
The Early Hairstreak Butterfly

I’m especially concerned for the risk to a very beautiful and rare butterfly known as the Early Hairstreak (Erora laeta). This specialized butterfly lives primarily in mature deciduous and mixed hardwood forests. The Hairstreak caterpillars live in the high canopy dining only on beech nutlets.

For me and for all of us, trees are more than shade. Trees reduce the impacts of heavy rainstorms and runoff, reduce summer heat, and provide paper and wood products (including the original Louisville Slugger baseball bat, made from ash). Much more than that, trees are critical components of wildlife habitat providing food and shelter to a vast array of native insects and animals.  Unfortunately, trees are often not appreciated until they are gone, because so much of nature goes away with them.


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