The emerald ash borer (Agrilus planipennis Fairmaire) is a pretty name for an attractive beetle, but don’t let this insect’s good looks fool you. It’s pretty, but in the 15 years since it was first reported, the emerald ash borer has the distinction of becoming the most destructive and economically ruinous invasive insect to make its way into the United States.
What is the Emerald Ash Borer and How Did it Arrive in Michigan?
The emerald ash borer is one of the stunning jewel beetles that calls northeastern Asia home. In that section of the world, very little attention is paid to the species because A) they’re really not common, and B) the trees the larvae feed on in their native environment have developed a natural defense against the insect so ecological damage is minimal. Entomologist who work in China, South Korea, and other countries where the emerald ash borer resides are quick to point out that the only trees that experience a noticeable negative impact to the insect’s presence are the ones that were stressed or starting to die before the beetles started laying eggs.
It’s believed that the species made the long journey from Asia via shipments of wood.
In the beginning, it’s likely that only a few of the insects were brought over, but as wood and other shipping materials were continuously shipped from one place to another, more and more of the beetles made the trip and found themselves in, what to them, must have seemed like an exotic land. The beetles quickly developed a fondness for all the nice ash trees they found here.
They settled in.
Started laying eggs.
When adult emerald ash borers land on an ash tree, they start chewing on the leaves. That’s not much of a problem. As the adults reach the end of their three-week life as full-fledged beetles, they mate, the female lays a few eggs, and they die, making room for the next generation. That’s when things start going downhill.
When the larvae hatch, they burrow through the bark and begin feeding on the tree’s vascular tissue, making it impossible for the tree to feed itself. When the larvae mature into its adult beetle phase, it chews its way out of the tree, creating a large exit hole. When portions of the bark are peeled away, you’ll see serpentine grooves in the vascular tissue. The grooves were created by the ravenous larvae. In the United States, the emerald ash borer don’t limit themselves to sick or dying trees. They’re laying their eggs on perfectly healthy ash trees.
After enough of the larvae have bored into the tree, the plant starves to death and the adult beetles move on, looking for another tree to infest and the cycle starts all over again.
The amount of time it takes for the larvae to completely kill an ash tree depends on several different variables, the most notable being the size of the infestation. The tree’s death can take anywhere from 2 to 5 years. Unlike trees in China and other countries where the emerald ash borer originated, North American ash trees lack a natural, built-in defense against the infestation.
The first place in the United States to experience an emerald ash borer infestation was Detroit, Michigan, who reported the discovery in 2002, but after analyzing tree rings, there’s evidence that the beetles actually arrived in Michigan during the 1990’s.
Detroit may have been the first known point of origin, but the beetles didn’t stick around there long. August 2017 reports show 31 different states, including Michigan’s upper and lower peninsulas, struggling to deal with this destructive pest. Ontario and Quebec are also engaged in what’s become a losing battle to save their ash trees.
The fact that the beetles are reported in so many different places and that they spread so quickly is a bit surprising. While the adult beetles do have the ability to fly, they’re not built for long distance flights, and generally only travel about a ½ mile, though if pressed, they’ll go as far as 3 miles. Most of insects have made the move from one state to another via the transportation of firewood and nursery trees.
Why You Should Care About the Emerald Ash Borer
Let me guess, you’re thinking: So, what? What do I care that some bug I’ve never seen is gnawing on a bunch of trees I can’t identify? They don’t impact me. You should think again. Ash trees are high value hardwood trees. In addition to being a favored landscaping tree, the lumber is used for a wide assortment of products, including:
• Baseball bats
• Bowling alley lane floors
• Wooden furniture
• Woodworking projects
• Canoe paddles
• And more
In addition to current commercial use, ash, particularly black ash, is incredibly important to the Kanienkehaka Nation, who revere the tree. Black ash basketry is an important part of their cultural heritage. Tribe members are working to protect as many black ash trees as possible, and collecting genetic specimens so they’ll be able to plant new heritage black ash trees whenever science comes up with a resolution for the emerald ash borer problem.
The Economical Toll of the Emerald Ash Borer
Prior to the first report of emerald ash borer in 2002, Michigan was home to over 700 million ash trees. In the past 15 years, the invasive species has resulted in the destruction of approximately 30 million ash trees just in Michigan’s southwestern region. That’s right. One single corner of the state. And the death toll climbs higher each year. The amount of damage the borer has already done to Michigan as well as in the surrounding states has made the insect the single most destructive and economically damaging invasive insect in North America’s history.
Michigan forests are filled with ash trees, many of which are now dead or dying, creating an ugly landscape, which is bad news when you consider that in 2014 travelers both in and out of state, introduced approximately $37.8 billion into Michigan’s economy. Many of those tourists come to the state specifically to enjoy the lovely forests, especially during the fall when the leaves are changing. While there are lots of pretty trees remaining, the ugliness the emerald ash borer leaves in its wake may be enough to convince people that they want to go somewhere else when they want to look at trees.
Economically speaking, it’s difficult to get a handle on just how much damage the insects have caused in the past fifteen years. It’s well into the billions of dollars. Even without considering the value of the lumber to insect has damage, the amount of money spent on the emerald ash borer each year is astonishing. It’s estimated that in a single year, state and federal resources spend a collective $29 million in a single year exploring way to fight back against the emerald ash borer. In 2010, it was estimated that if states chose to fight to save or has to remove just half of the ash trees being grown in urban settings, the expense would reach a whopping $10.5 billion.
Can the Emerald Ash Borer be Stopped?
At this point, most people in the forestry and ash industry aren’t optimistic about the future of the ash tree. The emerald ash borer has spread so quickly and the damage has been so extensive, that it’s unlikely many of the trees will survive. But that doesn’t mean anyone has quit trying to protect the trees which have withstood the problem thus far.
In their quest to stop the fast advance of the emerald ash borer in Michigan foresters and scientists have and are trying an assortment of options.
Tree trunk injections that consists of emamectin benzoate and which a 2010 study reported resulted in 100% larval mortality. The problem with the injections is that, while they’re highly effective, they need to be repeated every few years and the expense quickly adds up. It’s simply not logistically possible to inject every ash tree in every forest.
The release of small parasitic wasps that attack the emerald ash borer. These wasps were originally released in Calumet, Michigan as a 2010 test program. Since then, the wasps have been released in 29 different states. Entomologists are quick to warn that the release of the wasps isn’t going to do much to protect the current crop of ash trees, but they hope that the wasps will protect future ash trees from dyeing as a result of emerald ash borer infestations.
Researchers are also experimenting with genetics, particularly the genes and chemical make up of the blue ash species. For some reason, emerald ash borers leave blue ash alone. If an explanation is found, it’s possible that scientist will be able to use the information to come up with a way to not only better protect the current ash crop, but to also make future trees resistant to the invasive bug.
It’s possible a recently discovered blue ash tree may hold the secret the scientists are looking for. Unlike the rest of its kind, this tree had been hit by the emerald borer, but since the tree was stressed, and in their native environment emerald ash borers only go after stressed or dying trees, something in its chemical makeup must have changed which attracted the beetles. Hopefully, by comparing this tree to healthy, unaffected blue ash trees, scientists will isolate the exact chemical more quickly than they would have had this particular tree not been found.
Organic Solutions Emerald Ash Borer
If you have a stand of Michigan ash trees that you’d like to protect, possible things to consider include:
• Treating them
• Carefully inspect firewood for signs of emerald ash borer larval activity before purchasing it
• Do everything in your power to keep your stand of ash trees healthy and unstressed
• Contact a local arborist to discuss the possibility of giving your trees the emamectin benzoate injection
While all of these are great ways to protect your stand of ash trees from the emerald ash borer, the best, most organic method for keeping the invasive pest away from your trees is encouraging bats to move onto your property. How do you accomplish this? Easy. Provide them with a hospitable place to live. It’s not difficult. Simply build or purchase a few bat houses and mount them on a pole or wall that’s located near the ash trees.
Of the nine species of Michigan’s microbats, the one that’s both easy to attract to your property and that’s designed to eat large quantities of emerald ash borers is the big brown bat. Unlike the hoary bat and western red bat who are relatively solitary species, the big brown bat likes roosting in summer maternity colonies that can include up to 700 bats. Considering that each of these adult bats can eat more than half of its body weight in insects every single night, that’s bad news for any unsuspecting adult emerald ash borers that make their way onto your property and good news for your ash trees.
The catch is that the bats have to be present on your property before the adults arrive, so that they can consume the beetles before any eggs are laid, so you’ll want to have your bat house built, installed, and ready to go by late winter, before the big brown bats come out of hibernation.
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