Summer 2001 Volume 10, Number 2
EASTERN TENT CATERPILLAR INVASION 2001
Phil Marshall, Forest Health Specialist, Vallonia State Nursery
The forests of southern Indiana were invaded during April and May by a horde of caterpillars that prefers to feed one tree - Black Cherry. Commonly called bagworm or tent caterpillars by everyone, the proper common name of the caterpillar horde is Eastern Tent Caterpillar.
Eastern Tent Caterpillar occurs every spring and is easily recognized by the silk web in the branch axils on the inside of black cherry. Usually the number of caterpillars and their tents is very low and seldom noticed by landowners. However, the epidemic this spring was so massive that everyone in southern Indiana saw the silk webs and caterpillars.
Landowners and foresters reported the caterpillars completely striping the foliage from black cherry trees in the fence rows and the forest. Once stripped of all leaves, the caterpillars crawl in search of another tree to eat. Some landowners experienced the caterpillars crawling up the sides of homes and into their homes in their search for food. Foresters found the caterpillars feeding on oaks, beech, ironwood, other tree species and greenbriar when they could not find a black cherry. In some areas, mosses of cater-pillars were observed migrating across county roads in search of black cherry.
A question many people have is "Where did all the caterpillars come from?' Eastern tent caterpillar is present every spring some-where in Indiana usually at very low levels. They prefer black cherry and other fruit trees such as crabapple, but will feed on other tree species. In the spring of 2000, the caterpillars heavily defoliated black cherry in southern Monroe and northern Lawrence counties. Elsewhere in southern Indiana in 2000, they were at low levels, probably not noticed by everyone.
With the mild winter weather and low population levels of parasites and predators, the population of eastern tent caterpillar exploded in 2001. The mild winter did not kill eggs. And, the population of eastern tent caterpillar in 2000 was not high enough to support levels of parasites and predators that could provide natural control of the caterpillar.
In the 25 years of observing and recording forest pests in Indiana, I have not observed or remember an eastern tent cater-pillar epidemic of this magnitude. Anticipating your next question, yes the caterpillar will return in 2002 at or near the some level of defoliation. Generally, native defoliating caterpillars go into epidemic level for 2-3 years before natural control returns them to their normal low level presence. I believe 2001 to be the first year of the epidemic and 2002 will be the second year. After 2002, collapse of the population should begin. I expect parasitic flies and wasps to build their population levels in 2002 and start to control the caterpillar. Thus in 2002, people may complain about flies buzzing around them, which are the parasites that are controlling the caterpillar.
What will happen to black cherry? They will refoliate in May and June to near full foliage as if not stripped. The trees should sur-five with very little mortality expected this year. If the caterpillars return in 2002 and heavily defoliate trees again, then black cherry will start to die. Which black cherry tree will die is not easy to determine. However, trees stressed by heavy defoliation and drought are more likely to die. By 2003, eastern tent caterpillar should return to low levels and the threat of mortality will decrease and/or stop.
One other caution is defoliation later this summer by fall web-worm or Japanese beetle. Should one or both of them defoliate black cherry this year, the mortality risk greatly increases. Two defoliations in the some growing season are a severe stress to the tree.
To determine the amount of eastern tent caterpillar for 2002, examine the twigs of black cherry for the eggmasses. The eggmass has formed and will remain until next spring. Counting the number of eggmasses will indicate the amount of caterpillar next year. If you can easily find the black bond on twigs, expect heavy defoliation in 2002. Pruning twigs with eggmasses is one way to man-age the caterpillar.
For additional information or other questions on forest health, contact Phil Marshall, Forest Health Specialist, at the Vallonia State Nursery, 812-358-3621.