Boring insects are not boring, they’re serious pests

Boring insects are serious pests that can severely endanger tree health and kill a tree. While many species of boring insects are native to Michigan, they rarely cause as much wide-scale damage as an exotic or non-native borers does.

Many of the boring insects that attack trees are in the insect order Coleoptera or beetle family of insects. Well-known examples are the emerald ash borer (Agrilus planipennis Fairmaire) or Asian longhorned beetle (Anoplophora glabripennis) . However, other borers that can attack trees can also be from the order Lepidoptera (i.e. moths and butterflies) or the order Hymenoptera (i.e. wasps, bees and ants). Examples would be the banded ash clearwing, (Podosesia aureocincta); or the Sirex woodwasp (Sirex noctilio F.), respectively.

To a forester or arborist, wood borers attacking trees are never boring. The sign of borer infestation inside a tree is indeed serious business! That’s because insect borers, once they have really established themselves underneath the bark of a tree, are very difficult to control. While chemical pesticide options do exist, they can be expensive. In addition, sometimes trees are so weakened by borer attack and possibly other pre-disposing factors (old age, prior defoliation events, etc.) that they are just too weak to respond to treatment.

So, if borers are so dangerous to tree health, why can’t borers simply be prevented or treated right at the point of initial infestation? Well, borers by nature are often difficult to spot. For one, they typically leave only tiny-sized entrance holes and most of their life cycle is spent underneath the bark. Moreover, a number of the more serious borer insects (emerald ash borer, bronze birch borer and others) typically attack a tree in its upper most trunk and branches first – which makes it very difficult to spot until a significant amount of dieback has occurred.

There are many species of insect borers in nature. For almost any deciduous and conifer tree species - you could probably find some type of boring insect that could attack it , if you look long enough through reference books on insect pests. Borers are just part of nature. However, in many cases, our native borers seem to prefer to attack trees that are old and weakened. It’s just not as common to see native borers attack vigorous, healthy trees.

However, for some of the more “notorious” borers making the news these days – that’s not the case. Both emerald ash borer and Asian longhorned beetle can be found attacking stressed as well as healthy trees. Both of these boring insects are species that are not native to this country. As such, these species have not evolved with our trees and forests and so it seems that our native trees have a difficult time warding off these borers. Consequently, as in the case of emerald ash borer, this insect is killing millions of native ash trees in Michigan as well as across the United States.

At this point in time, the Asian longhorned beetle has not yet established itself in Michigan. And it would be nice to keep it outside of Michigan’s borders. That’s because the Asian longhorned beetle can attack many species of deciduous hardwood trees – including sugar maple and all other hardwood species. Sugar maple just happens to be one of the most common tree species in Michigan. It can be found growing all across both peninsulas of Michigan. Therefore, the threat to our Michigan forests is considerable (and potentially devastating) if Asian longhorned beetle establishes itself in Michigan.

Fortunately, Michigan citizens can help forest health specialists keep Asian longhorned beetle (and other insect pests) at bay. Landowners can “adopt” a tree (i.e. called a Sentinel Tree) in their yard or woods to monitor and keep an eye on. They can go on-line and report back what they see happening to their tree over time. It’s all part of the Michigan Eyes on the Forest and Sentinel Tree Network.

Funded by the Michigan Invasive Species Grant Program, the MSU “Eyes on the Forest: Invasive Forest Pest Risk Assessment, Communication and Outreach Project,” links research with outreach and communication projects through the MSU Department of Entomology and Michigan State University Extension.  For more information, go to the Michigan Eyes on the Forest webpage or the Midwest Invasive Species Information Network webpage.

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