Gypsy moths defoliated this Michigan
forest. The photograph was taken in July.
A single gypsy moth caterpillar
may eat 9 square feet of leaves during its lifetime. Gypsy moth
caterpillars can be identified by the prominent blue and red
dots along their backs.
On my return from a recent trip the woman next to me on the plane asked why I had gone to Pennsylvania. When I told her, she exclaimed, "You went to a four day conference to discuss one bug?"
That threw us into a long discussion on the pros and cons of bugology, know in some circles as entomology or the study of insects and their relatives.
Being a plant pathologist by training, I could understand her aversion, and her dismay that this one bug, the gypsy moth, is causing so much concern. Like many exotic species brought into the United States, gypsy moths have few natural enemies to keep their numbers in check. With the abundance of food, oak and other deciduous trees, the moth is slowly marching across the United States. And we can do little to stop it.
It already occupies most of northeastern United States, from Maine to Michigan, northern Ohio and North Carolina. Under normal conditions, moth populations spread about 15 miles per year. That means the moth will be in Missouri around the year 2030. That seems like a long way off, but there are two problems. First, when the moth gets here, it will the cost the state many millions of dollars in lost forest products, tourism and real estate revenues, so we need to be prepared. Second, the moth can hitchhike to new locations easily and thus spread at a much faster rate.
For instance, in 1992 Arkansas discovered a population near Compton, about a half hour south of Branson. It probably started with gypsy eggmasses brought in on an RV. When the eggs hatched, they started an infestation.
Over a few years, the population grew to 10,000 eggmasses per acre. While visiting the site, I found cream-colored eggmasses, about the size of a quarter, plastered all over the trees, rocks and building to imagine what this looked like, I think of the density of bubble gum wads on the bottom of bleacher seats at the local junior high school.
A gypsy moth trap (left) contains a chemical that attracts the males. Gypsy moths can hitch hike via eggmasses (right).
Missouri is bracing for an onslaught of moths that may not come for 30 years.
Gypsy moth caterpillars (left) can kill trees in the second season of their attack. When you inspect your vehicle for
eggmasses, also look for gypsy moth pupae (right).
Caterpillars had stripped 50 to 75 percent of the leaves off the white and blackjack oaks. Trees stripped at this rate can die if attacked a second year in a row. Even the dogwood and red cedar, which gypsy moths usually won't feed on, were covered with eggmasses, probably because of competition for space. In 1993, tornado winds blew the young caterpillars many miles out of the area, perhaps starting more gypsy moth infestations.
Arkansas is working hard to eradicate the gypsy moth before it can spread any more. The U.S. Forest Service working closely with Arkansas officials to control the gypsy moth using either one of two products: BT or Dimilin. Bt is a toxin produced by a common soil bacteria that affects only butterfly and moth caterpillars. Dimilin is a growth regulator that prevents molting in young insects, crayfish and their relatives.
Neither of these products have the long term residual or broad range of affected species that were trademarks of older pesticides. In addition, neither product directly affects humans, mammals or fish.
Although management efforts in Arkansas have been successful in reducing moth numbers, getting rid of the gypsy moth will be difficult. Experts predict it will take three to five years of treatment to control this heavy population. In the meantime, we in Missouri have to watch for moths moving across state lines.
Surveys found 25 to 30 moths in Taney County in 1993 that we think came from Arkansas. In 1994, only seven moths were caught in the area, so perhaps any caterpillars or moth blown in from Arkansas did not survive to set up camp. If they do in future years, we want to be there to control them.
Why is the gypsy moth so hard to stop and why are we so worried? The caterpillars are active spring feeders that can eat 9 square feet of leaves during their life. Large populations of caterpillars have completely defoliated forests in other states.
Losing their leaves in spring forces the trees to put on new leaves that same season. This greatly stresses the trees. Severely stressed trees are less likely to withstand drought or defend themselves against other insects or diseases. During the first several years of an outbreak, tree mortality can range from 10 to 85 percent, depending on the health of the trees and the species mix.
The healthier the stand the better it is able to recover. The better the mix of tree species, the better the forest is able to replace dead trees with other less susceptible to the gypsy moth. In Missouri, the high percentage of oaks and poor growing conditions make our forest vulnerable to severe tree mortality. This mortality will have direct and indirect impacts on other plant and wildlife communities and the economies that depend on them.
Gypsy Moths
Male Gypsy Moth (left) Regular scalloped lines parallel to wing edges. Smaller than female.
Female Gypsy Moth (right) Cream colored. Large body with same scalloped lines on wing as male
Not to draw an overly bleak picture, the gyps moth will not destroy the forest, but it will drastically change it. Weakened trees will begin to die. Trees not preferred by the moth will increase. In Missouri that means ash, black locust, dogwood, red cedar and hickory may begin to dominate areas that had been predominately oak.
Wildlife species will shift depending on their favorite breeding sites and food source. Birds that nest high in the forest canopy may decline because of exposure to predators. Woodpeckers may increase because of more dead standing snags. Wildlife species dependent on oaks may decline.
Because dying oaks will open the canopy and let in more light, shrub and understory species will increase along with the animals that feed on them. Water quality will be affected by large amounts of leaf bits and insect droppings falling in streams and lakes. This will affect aquatic species, favoring some and discouraging others.
Look Alikes
Tussock Moth (left) Erratic diamond patterns on wing. Smaller than male gypsy moth.
Underwing Moth (right) Erratic zig-zag lines on wing. Larger than male gypsy moth.
Forest-related industries will not be destroyed either, but they will be force to change their emphasis and broaden their scope. Timber markets dependent on oak will decline, so those less dependent on oak may be expanded. This could affect everyone from the logger to the furniture manufacturer.
Tourism will be reduced when trees are stripped of their leaves and when large numbers of caterpillars create a nuisance (May to July). As a result, tourism industries may need to refocus marketing strategies to other times of year. Land prices may decrease in areas with highly susceptible forests. All of this will greatly change the character of Missouri's natural resources and related industries.
The Missouri Department of Agriculture has developed an extensive survey program to detect spot infestations and to delay the permanent establishment of the gypsy moth in Missouri. With the help of several other agencies and private groups, thousands of detection traps are put up each year along roads and in high-use areas.
These small cardboard traps contain a chemical that only attracts male gyps moths. This chemical, known as a pheromone, is naturally released by female gypsy moths. Males following the scent to find a mate, find a sticky trap instead.
Each year, the results of the detection survey are used to determine if spot infestations exist and where they may be. When an infestation is found, the site is searched for eggmasses to determine areas to be treated. So far, no infestations have been found in Missouri, so no treatments have been made.
Although state and federal agencies are working hard to keep the moth out of Missouri, they need your help. Residents moving out of infested areas needed to inspect their out door belongings to prevent transporting the moth. Look for fuzzy eggmasses and pupae like the pictures shown here. Tourists traveling to infested states during the time of egg laying (July through September) should also inspect their vehicles before returning home.
Anyone importing wood or nursery products can help by notifying the Department of Agriculture, so they can monitor moth movement between states. If you find gyps moth eggmasses, pupae or moths, let the Department of Agriculture (573-751-5505) or the Conservation Department (573-751-4115) know so they can inspect and monitor the area.
Landowners can also help, particularly those with relatively inaccessible forest land. If you would like to participate in the detection trapping program or wish to receive future gyps moth news, please write the Forest Health Specialist at the Missouri Department of Conservation, P.O. Box 180, Jefferson City 65102.
By Sue Burks, photography by Jim Rathert, illustrations by David Bessenger
Reprinted from the April 1995 Missouri Conservationist
Copyright (c)1995, by the Conservation Commission of the State of Missouri
