Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
7/7/03
Contacts:
Mark Shour, Entomology, (515) 294-5963, mshour@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning July 11, 2003
Gypsy Moth, an Unwanted Insect in Iowa
By Mark Shour
Extension Entomologist
Iowa State University
Iowa has its fair share of insect pests. European corn borer, bean leaf beetle, boxelder bug, carpenter ant, fall webworm, Japanese beetle, and various aphid, grasshopper and mosquito species top the list of common insect pests reported to Iowa State University each year. One insect that Iowa does not need is the gypsy moth, Lymantria dispar.
Moving West
The gypsy moth was brought to Massachusetts in the late 1860s in an attempt
to improve the silkworm industry. As legend has it, the insect escaped
captivity after a storm and moved into the oak forest canopy, remaining
undetected for several years. From Massachusetts, this new pest moved
north into Canada, west to Indiana and Michigan and south to North Carolina.
To date, Iowa is free of this pest but the westward fronts involve areas
of eastern Illinois and Wisconsin.
Big Appetite
The gypsy moth is one of North America's most devastating forest and shade
tree insect pests. Common host plants include oak, apple, basswood, birch,
hawthorn, poplar, sweetgum and willow, but this insect is a veritable
“garbage disposal- of available foliage during population outbreaks.
It is the caterpillars (larvae) that eat the foliage on host trees, often
totally defoliating one host before moving to an adjacent tree. Accounts
of thousands of acres of oak woodlands defoliated by the gypsy moth are
common in the eastern United States. Unlike other common caterpillars,
this pest feeds at night and rests on foliage or tree trunks during the
day, where you could spot them if you have keen eyesight.
Colorful Caterpillars
You can recognize gypsy moth caterpillars by their distinctive color pattern.
Caterpillars are hairy and gray-black, with a yellow-orange head and two
rows of wart-like spots down the center of the back. The first five pairs
of spots are blue and the remaining six pairs are red. Full-grown caterpillars
are approximately 3 inches in length. Gypsy moths usually feed during
late May and June, maturing by early July. The insects then molt to the
pupal stage, when the transformation to the adult stage occurs.
Adult Escapades
Adult female moths are heavy-bodied and creamy-white with distinctive
black wavy lines on the hindwings. Although females have two pairs of
functional wings, they do not fly. To compensate for this limited mobility,
females emit a powerful sex perfume (“pheromone-) to attract males.
Adult male moths are light brown with black markings on the wings and
fly in zigzag patterns searching tree trunks for females during daylight
hours. After mating, females deposit several hundred eggs in groups (called
“masses-) during July; these masses are tan. Females place egg masses
on tree trunks, stones, houses or other “stationary- objects. Unfortunately,
egg-laying sites also can include firewood, recreational vehicles, cars,
trucks, lawn furniture, trailers and trees in landscape nurseries. Egg
masses sit idle until the following growing season, when tiny caterpillars
emerge looking for green leaves to devour.
Traveling Incognito
If egg masses were deposited on truly stationary objects the previous
year, caterpillars crawl to the top of trees, lay down silk threads and
begin feeding on leaves. If this period is windy, the caterpillars can
be spread to nearby trees (“ballooning-). This process accounts for
the local spread of gypsy moths. If egg masses were placed on movable
items and carried to new areas of the United States, new infestations
can occur as the caterpillars feed on available host foliage. To the untrained
eye, the gypsy moth is just another bug feeding on plants.
Controlling Forces
Management of gypsy moth populations in infested areas has occurred from
the1890s to the present. Early control efforts involved spraying foliage
with insecticides, treating egg masses with creosote, and banding tree
trunks with sticky materials. Modern methods include use of insects that
are natural enemies, treating foliage with Bacillus thuringiensis (bacteria
toxic only to caterpillars), quarantines of nursery stock from areas known
to be infested, mating disruption techniques and trapping of male moths
with female sex pheromone. “Slow the Spread- is the national effort
to limit the movement of gypsy moth into new areas.
The primary preventive strategies in Iowa involve nursery stock quarantines and trapping male moths. If a small gypsy moth population is found in the state, a quick, organized response by the Iowa Department of Agriculture and Land Stewardship (IDALS) eliminates the incursion. As a participant in trapping efforts this year, I was encouraged by the dedication and persistence of the agencies involved. More than 5,000 pheromone traps are now in place at strategic locations across Iowa, thanks to the efforts of IDALS, the Iowa Department of Natural Resources, the United States Department of Agriculture, city foresters, and Iowa State University. If you see one of these orange, triangular traps in a tree or on a post, do not disturb it. These traps will be collected by Labor Day and may hold information as to which areas of the state need immediate attention from IDALS.
Future of Iowa's Forests
Although most of Iowa's land mass is used for farming, significant and
irreplaceable tree stands exist throughout the state. Continual monitoring
for isolated gypsy moths entering the state are vital to protecting Iowa's
trees. Landowners and commercial arborists who notice unusual defoliation
(especially on oak trees) can work together with state and federal agencies
to keep the gypsy moth out of Iowa.
-30-
ml: isugarden
|
Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The fullsize photo is 252K. Caption: Gypsy moth larva. Photo by Scott Bauer, USDA ARS. |
 |
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.