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Special Edition, August, 2003  
By Bill Cook

     So, you've noticed the gypsy moth impacts?  This summer has seen several leaf-eating caterpillars working on our trees.  But gypsy moth is probably the one we'll be hearing more about over the next couple of years.

     Gypsy moth larvae are hairy with numerous pairs of blue and red dots on their back.  They were introduced to North America in 1869 by a Frenchman named Truevelot.  He was an amateur naturalist living in Massachusetts who wanted to breed a disease resistant silk moth.  A few caterpillars escaped, became established in Massachusetts, and this exotic pest has been spreading ever since.  The first known gypsy moths were found in Michigan in 1954.  State officials tried for years to eradicate the pest but the first outbreaks occurred in the Midland area in the early 1980s.  Gypsy moth has been in the Upper Peninsula for at least ten years, with simmering populations in Dickinson, Menominee, Delta, Marquette, and Schoolcraft counties, as well as most of the eastern UP.

     At this time, the flightless female moths are about finished with laying egg masses on trees, buildings, and just about any surface that attracts them.  If you see light brown cottony patches about an inch or two long, they might be the egg masses.  About the time the fishing opener begins next spring, eggs will hatch and the new, tiny caterpillars will find plenty of good host trees to feed upon in the Upper Peninsula.

     Eggs hatch in May, the caterpillars feed through June and into July, pupation lasts for 7-14 days, then the adults emerge and mate.  Each female lays one egg mass and each egg mass can contain 500-1000 eggs.  The female moths like to lay their eggs in sheltered or protected places.  They are commonly found on the underside of large branches but egg masses sometimes appear on the wheel wells of trailers, on boats, lawn furniture, firewood, and similarly protected spots.  By the end of August, all is quiet until spring.

     Gypsy moth is a defoliator, meaning they eat leaves.  Their diet consists of hundreds of species, but prefer oaks, apples, willow, birches, and aspens.  Larger, older larvae will also eat some conifers such as hemlock, white pine, and spruce.  Usually, the defoliation does not kill hardwood trees but conifers are less resilient.  The stress of two or three years of defoliation, in combination with other factors, will sometimes cause trees to die.  With recent droughts, recent forest tent caterpillar defoliation, and the advance of oak wilt disease, our oak populations in the southern U.P. are at high risk.

     Perhaps more important than the tree health issue, is the impact on people.  High populations of gypsy moth caterpillars result in a "rain" of frass, a term that describes plant parts and feces that drop from the feeding caterpillars.  Swarms of migrating larvae might be found all over homes, walkways, and outdoor furniture.  Walking barefoot may be unpleasant for a couple years.

     What can be done?

     The gypsy moth is not going to go away.  It has become part of our forest landscape.  History shows the first outbreaks in an area are often most severe.  Later outbreaks usually moderate as the natural systems absorb the new species.

     Pesticides can be used to kill gypsy moth caterpillars but most conventional insecticides will kill many other insect species, including many beneficial ones.  Another type of product called Btk, or "Bacillus thuringiensis kurstaki", can be purchased at most garden stores.  It affects foliage-feeding caterpillars but not beneficial species such as predatory insects or honeybees.  However, application to the crowns of tall trees can be difficult.

     Homeowners can "band" individual trees with folded burlap.  Gypsy moth caterpillars will hide under the burlap during the day and can be swept or picked off and drowned in soapy water.  Sticky-tape can be applied on the band to help capture larvae but don't put sticky material directly on the tree.

     A number of natural enemies do feed on gypsy moths.  Some birds such as the black-billed cuckoo will feed on larger caterpillars.  The black-billed cuckoo populations have risen in the last couple years in response to the forest tent caterpillar outbreaks.  Chickadees sometimes feed on the egg masses.  Mice, voles, beetles, wasps, tachinid flies, spiders, ants, rodents, and other organisms will also feed on various stages of gypsy moth.

     The best defense is to maintain healthy trees before and during an insect attack.  A healthy tree will tolerate defoliation much better than a tree that is drought-stressed or has been wounded by lawnmowers.  Water is generally the key to keeping trees healthy.  Give shade trees an inch of water a week throughout the growing season.  Good forest management practices including maintaining proper stocking and avoiding wounds will keep forest stands healthy.

     The 2003 gypsy month season is over but you can bet this exotic pest will be back.  Watch for more information this spring.  Contact the MSU County Extension Office for updates and bulletins.

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Prepared by Bill Cook, UP Extension Forester, 6005 J Road, Escanaba, MI  49829
906-786-1575 (voice),  906-786-9370 (fax),  e-mail:  cookwi@msu.edu
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Last update of this page was 05 September 2003




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