wpe5.jpg (2127 bytes)U.P. TREE  IDENTIFICATION  KEY
from Michigan State University Extension


Exotic species are identified with red text. Insects are divided into five categories; 1) defoliators, 2) bark beetles & wood borers, 3) terminal feeders, 4) sucking insects, and 5) parasites & predators. If attempting to identify 'what's eating your tree' then you'll need to know where the insect is feeding and what tree species is affected. Of course, only a sampling of forest insects are mentioned here.



Defoliators eat the leaves of trees, their infestation sometimes reaching epidemic proportions.  Presence of these insects can easily be detected by the loss, deformation, or discoloration of needles on conifers or the summer loss, deformation, or discoloration of leaves on hardwoods.  Resulting loss of the tree’s food manufacturing ability causes a slowing of timber growth, and in the case of sugar maples, can seriously affect sap production.  Conifers can be quickly killed, or lose their form if intended as Christmas trees.  Hardwoods, however, can usually withstand several years of defoliation without death.  Fortunately, epidemics are usually cyclic and the insect boom will collapse through starvation or other natural checks and balances before the forest is irreversibly damaged. Many of these species are moth, butterflies, and wasps.




Bark Beetles include over 100 insect species and are among the most destructive in North America.  It is estimated that approximately 60 percent of all tree growth loss is due to these burrowing pests.  Bark beetles excavate egg galleries in fresh phloem, the inner bark which carries food from leaves to the roots of a tree.  When the eggs hatch, hundreds of larvae eat their way from the main gallery, mining the inner bark in all directions.  The pattern of their work is like a fingerprint for the species, and their collective eating nearly always spells doom for the tree.  The first easily noticed sign of this is a reddening or fading appearance in the top of the tree, followed by complete browning.  Less noticeable are patches of pitch or sap seeping out where the insects first entered the trunk.  These insects are usually only a problem in mature or maturing trees, or stressed trees, but some species plague young plantations.

Wood borers go deeper than bark beetles, doing their damage in the sapwood and even the heartwood of a tree.  But while some wood borers attack living trees, others drill into recently cut logs, lowering their value for lumber or pulp.  Some even attack finished lumber.  Often the tunnels have a secondary effect of providing an entry point and channels of spread for fungus (rot). Although not true of all species of wood borers, telltale sign is often the sawdust and other wastes that accumulate outside holes in the trunk or limbs. The best defenses against many members of this group are to keep trees healthy, vigorous and undamaged, and to sell or use cut trees quickly rather than letting them lie around.  This is especially important during the summer. Common families include the Cerambicids and Buprestids.




Terminal feeders eat buds or root tips.  Some species in this group also do their damage by girdling twigs.  Their attacks are fatal only if repeated year after year, so their real damage is in the deformities caused as a tree overgrows its injured buds.  This often slows growth as well.  Root insects, mostly white grubs, some borers and root weevils, are problems only in seedlings and ornamental shrubs. Entomologists suggest that many terminal insect problems could be avoided by more carefully matching planted species with the site conditions of their natural range. Most of these species are moths and beetles.



This group is named because its insects have sucking mouth parts and feed on plant fluids.  A huge number of species are included, but few cause actual death to trees.  Their main offense is robbing the tree of its food and water.  This, of course, will eventually affect growth and health.  They are also known to spread tree diseases and sometimes the slits they make in branches weaken the branch enough that it dies or snaps off. True bugs are most common order.




A large number of insect species prey upon other insects that are tree pests. These parastic and predatory insect populations "boom" when their prey populations experience outbreaks. This is part of the natural controls for cyclic outbreaks of species such as forest tent caterpillar, spruce budworm, and (now) gypsy moth. Some of the more interesting (gruesome!) life cycles are associated with this group of "good" insects.

Image Citations
Ichneumonid wasp -
Boris Hrasovec, Faculty of Forestry, Bugwood.org

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This site created and maintained by Bill Cook, MSU Extension Forester for the Upper Peninsula of Michigan.   Editing and modification is ongoing.  Submit suggestions, questions, and corrections to cookwi@msu.edu or call 906-786-1575. 


This site is hosted by School of Forest Resources and Environmental Science
at Michigan Technological University.

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