LARGE-SCALE DEFOLIATION BY GYPSY MOTH IN PENNSYLVANIA:
INFORMATIONAL BASIS FOR RESPONSE TO HIGHLY DYNAMIC INFESTATIONS
John W. Quimby
Pennsylvania Department of Environmental Resources
Bureau of Forestry, Division of Forest Pest Management
34 Airport Drive
Middletown, PA 17057-5021 USA
ABSTRACT: Gypsy moth was intensively controlled up until 1968 when various
economic and environmental considerations make it impractical. Since then,
there has been a series of epidemics of gypsy moth within the Commonwealth of
Pennsylvania that have caused a variety of impacts that have affected the
political, economic, and social fortunes in a variety of habitats,
physiographic provinces, and ecological settings. The technological and
managerial tools have evolved during the last 25 years such that there are a
multitude of options available to the resource manager to confront,
ameliorate, and accommodate to gypsy moth epidemics. The decision-making
process has become unique for each forest stand. The paper addresses the
decision-making process and the informational basis behind that process.
INTRODUCTION
The gypsy moth was introduced into North America late last century. In the
early days there was a large effort to eradicate the gypsy moth before it
spread. Millions of dollars were spent in the effort -- and that was when a
million dollars was a lot of money. The most effective pesticides were used
with little regard for side effects. Lead arsenate and DDT probably accounted
for 95 percent of the volume used up to 1965. With the curtailment of DDT,
the gypsy moth was irresistible. Every other registered insecticide killed
only 70-95 percent of the gypsy moth. With a reproductive potential of 500,
they were able to repopulate some areas within one year. Even if reproductive
potential was only 100, they could still keep even. There was no stopping
gypsy moth -- they relentlessly progressed across Pennsylvania in 22 years
(it would have been faster if the prevailing winds would have been from the
Northeast).
In the early 1970's, the gypsy moth did us an enormous favor and itself a
disservice: it went epidemic in the Pocono Mountains of Pennsylvania. There
have been epidemics of greater extent and severity by other insects in other
areas of the state before 1970 without much attention from state legislators.
However, the residents of the Poconos, it seemed, really knew how to pull the
right strings. It was at that point that the gypsy moth became a political
insect in Pennsylvania.
Within a couple of years we had sufficient funding to build a biological
control laboratory and to conduct an aggressive aerial spray program. We
began an exotic parasitoid rearing program in 1972. Through foreign
exploration cooperators, the USDA Forest Service, and the Agricultural
Research Service, we have cultured 28 species of parasitoids of five families
of Hymenoptera and one family of Diptera.
The impact of gypsy moth on Pennsylvania's forests has been both great and
small. There has been considerable impact and negligible impact. The gypsy
moth leaves a path of destruction and is hardly a nuisance. You may ask,
"What's this oxymoron talking about anyway?"
All of these contradictory statements are true to a certain degree. Of
course, they cannot all be true to the same person, at the same time, in the
same place. However, given different perspectives by virtue of time and space
shifts, the consequences of gypsy moth can be both devastating and innocuous.
It is true that there is an association between tree mortality and gypsy
moth. It is also true that millions of trees have died that were in the path
of gypsy moth epidemics. During the past 21 years, gypsy moth has defoliated
an average of approximately one million acres each year. With an estimated
8.8 million acres infested, there have been numerous tracts of forestland that
have received multiple defoliations. The result of two or three defoliations
in as many years is often that 30 percent or more of the oak trees die. In
years of rainfall deficits or when other stress occurs in combination with
severe defoliation, the percentage of oak mortality may exceed 50 percent or
even 80 percent. This situation has occurred fairly often in the last decade.
There were several droughty years in the 1980s and in 1991.
Forest insect epidemics are probably not unique to the industrial age.
There are several insects that are indigenous that cause widespread heavy
defoliation. Even if they didn't, there have always been fires and droughts
affecting our forests negatively. In spite of these and the ravages of some
40 species of exotic pests (e.g., the chestnut blight, Dutch elm disease, and
several sawflies) plus the complete havesting of the forests of Pennsylvania
early in this century, the forests of Pennsylvania on average today are
verdant, growing, and overall, healthy. The reasons? The forest has a
tremendous capacity to ameliorate the effects of almost any catastrophic
event. Even where overall tree mortality exceeded 60 percent following a
gypsy moth epidemic, there has been enough growth on surviving trees and
enough new trees that grew into the stands that, after eight or so years,
these stands usually regain the lost volume and values (Quimby 1990).
The USDA Forest Service inventoried the forest resources of Pennsylvania
in 1978 and again in 1989 (Alerich 1993). This coincides with at least three
epidemics of the gypsy moth during the same period. During that period in the
gypsy moth infested areas, approximately 35 percent of stumpage died on
960,000 acres of forestland. An additional 105,000 acres were similarly
affected in 1988 and 1989 (Quimby 1990).
Indeed, the Forest Service inventory showed approximately the same amount
of tree attrition as what we have observed in our surveys. Yet, when the
total stocking was compared between the two inventories, there were
significant increases. The oaks showed some losses in percentage
representation. But not even all the oaks were losers; northern red oak
showed an 11 percent gain!
Nor were the changes uniform across the size classes. The smaller size
classes (6 inches, 8 inches, and 10 inches) were less well represented in the
1989 inventory compared to the 1978 inventory. The larger size classes (12
inches, 14 inches, 16 inches, 18 inches, and 20+ inches) all showed gains.
Volume gains occurred in red maple, pine, hemlock, birch, and other species.
All growing stock volume increased 15 percent; sawtimber was up 32 percent;
red oak sawtimber went up 30 percent.
The fact that we have gains in stocking and size and species diversity
statewide is small consolation to the forest landowner who has a large tract
of prime oak veneer-quality sawtimber and watched it get defoliated several
years in succession and then saw 50 percent of the trees die, the consequences
of which can be the loss of tens of thousands of dollars in timber value.
Also, it is of small comfort to those folks who are squeamish about small,
hairy crawling things and have to endure three weeks of defoliation, frass
precipitation, and hordes of migrating caterpillars in their retreat in the
woods.
The results of these scenarios range from hysteria and anger to apathy and
acceptance in a broad range of people from housewives to girl scouts, from
wooded-residential landowners to resort frequenters, from tree lovers to
foresters, from town councilmen to federal legislators. The result of this
sequence has been usually appropriations by local, state, and federal
legislators with the belief that with enough money, we can drive these
obnoxious critters back to France where they belong. They all want relief,
and they want scientists to provide it -- now!
The reality, though, is that, even with ten times as much money, science
can only provide temporary relief. The knowledge that we have and the tools
that are available are insufficient to manipulate such a respectable foe.
And, even if we could, we certainly do not have the ability to manage into
oblivion other catastrophic tree tormentors such as oak leafroller, pear
thrips, late-winter freezes, and drought.
Even if we did figure out all the appropriate questions and were able to
come up with the appropriate answers to those questions, and then apply them
to yield suitable solutions to these puzzles, the gypsy moth would change the
rules, and either evolve or modify some aspect of its behavior (like the
introduction of flying female) to thwart our best, and most organized,
management schemes. In sum, we had better learn to coexist with gypsy moth
because it has immigrated despite the war we have waged on it for the last
hundred years.
So that brings me to the question at hand and the theme of my presentation:
how do we respond to these highly dynamic infestations?
As I said before, this has not been an easy process. So many factors must
be considered:
A. Economic Factors
1. Income from forest?
2. Damage level determination - intensity of management effort
3. Loss of values of the future and present
a. Timber - loss of growth and loss of stumpage.
b. Recreation - aesthetics, hazard, discomfort.
B. Political Factors
1. Local and state elections - a political issue
2. Legislative mandates
a. Protect the forest.
b. Don't just stand there, do something! Funding results.
3. Responses by forest management personnel
a. Spray as much as we can.
b. Spray only certain tracts.
c. Promote biological control agents.
C. Technological Factors
1. Advancements in spray application technology
2. Advances in Bt and other insecticide technology
3. Gypsy moth fungus technology
4. Advancements in viral, parasitioid, predator, and mechanical control
tools
D. Legal Factors
1. Pesticide Act
a. notification.
b. buffer zones.
c. dosage.
d. timing.
e. overspray.
f. water contamination.
E. Social Factors
1. Activist movement
a. prospray - Entomophobia, foliage lovers, timber husbands.
b. antispray - "environmentalists."
c. ambivalent individuals.
2. Hypersenitive individuals
a. spray sensitive.
b. urticaria and other allergies to larvae, moths, and eggs.
F. Landowner Factors
1. Save the forest -- spray it all.
2. Tree species diversification -- spray only certain areas.
3. Do nothing. Why worry, since growth exceeds removals statewide?
G. Ecological Factors
1. Effect on nontarget critters.
2. Effect on biodiversity - will we lose some species?
3. Effect on species of special concern (rare and endangered species).
In conclusion, we have adopted a rather ponderous decision-making process
that is in a constant state of evolution and addresses the needs and desires
of an array of affected people. Some of the projects and activities in which
we in the state organization have engaged include:
A. Spray to alleviate the nuisance and protect certain high-value stands.
B. Encourage natural enemies, e.g., whitefooted mice, Calosoma beetle, and
Entomophaga maimaiga, plus 28 species of parasitoids.
C. Adopt various predictive tools.
1. susceptibility ratings
2. vulnerability ratings
3. identification of forested areas that meet the guidelines (qualified
treatment areas)
4. implementation of a geographic information system
a. to store qualified treatment areas
b. to store topographic information
c. to store historic weather data
d. to store defoliation and spray history
e. to store land ownership information
5. Participate in a decision-making model -- a cooperative effort between
several northeastern states, the USDA Forest Service, and the SUNY of
Syracuse, New York. This system is being developed to help forest
managers by incorporating all the technological tools and pest
attributes that are computer compatibile to produce the choices and
perhaps even identify the best choice.
The bottom line, as with most natural disturbances, is: even though the
short-term consequences can be inconvenient -- even downright costly to some
folks -- the long-term effects are not so bad statewide. After the smoke
clears and the dust settles, there's still a forest out there -- and it looks
pretty good. In my opinion, the best thing you can do to deal with
catastrophic events such as gypsy moth and the consequences of its epidemics
is to try to minimize the short-term losses and accept the inevitable.
LITERATURE CITED
Alerich, Carol. 1993. Forest statistics for Pennsylvania - 1978 and 1989.
USDA Forest Service, Northeastern Forest Experiment Station Research
Bulletin NE-126. 35 p., 157 tables.
Quimby, John W. 1990. Tree mortality following gypsy moth epidemics - 1990.
Unpublished report, PA DER Bureau of Forestry, Middletown, PA 17057.
3 p., 32 tables.