A GYPSY MOTH POPULATION STUDY IN THE UPTON ECOLOGICAL AND RESEARCH RESERVE, BROOKHAVEN NATIONAL LABORATORY, UPTON, NEW YORK

By Christopher Duffner,

Longwood High School Science Department,

Longwood High School, Middle Island, NY.

Acknowledgement: The following Longwood High School students contributed to this project by assisting with egg mass counts, gathering information from internet resources and organizing and analyzing the data: Joan Burger, Chris Cells, Katie Finnigan, Sean Flood, Michael Guss, Paula Huang, Jeanne Imhof, Jennifer Rosenthal, Leahana Rowehl, Kurt Spielmann, and Adam Yakaboski.
 

Introduction

The gypsy moth (Lymantria dispar) is one of the most important defoliating pests in both forested and residential areas in the northeastern United States (Thorpe, 2001; Shetlar et.al., 1999; Buss et. al., 1996; Thorpe et. al., 1995; Klass, 1990). Since its introduction into the U.S. near Boston, Massachusetts in the late 1860's (Baker, 2001; Shetlar et. al.; Liebhold et. al., 1998), it has expanded its range to include all of the northeastern states, and most of the mid-Atlantic states. Damaging populations have been reported as far south as North Carolina, and as far west as Michigan (Solomon, 2002; Baker; Shetlar et. al.). The presence of significant populations of gypsy moths, as well as the defoliating effects of those populations, on Long Island, has been observed and documented for at least the past twenty five years (Baker), and probably longer. "…Gypsy moth populations typically thrive on Long Island and elsewhere in coastal New England." (Liebhold, 2002)

Gypsy moth egg masses over-winter on tree trunks and branches, as well as on houses, fences and a variety of other surfaces. Larvae generally emerge from mid-April to early May, depending on local conditions (Baker). This is timed to coincide with the emergence of the leaves on which they feed. On Long Island, there is generally a time lag as one progresses form west to east for both leaf and gypsy moth larvae emergence (Cornell Cooperative Extension Bulletin, 2002). Newly emerged larvae will climb in search of leaves to eat. They may spin silken threads to suspend themselves from branches, etc. and may be transported by the wind to nearby trees, a process known as "ballooning" (Shetlar, et. al; Klass). The larvae pass through several growth stages known as "instars," punctuated by molts. The various larval stages, during which active feeding occurs, last for about seven weeks (Klass), after which they pupate. Most of the defoliating damage is done by older caterpillars during the last two weeks of June (Shetlar, et. al) or early July (Gage, 1996). Ten to fourteen days later, the adult gypsy moths emerge. Adult female gypsy moths do not fly and remain near where they emerge from their cocoons. They emit pheromones to attract the male moths, and, after mating, deposit the eggs in a single egg mass. Depending on location, this can occur from July to September. The adult moths die soon after reproducing. The egg masses then remain on the tree (or other object), until the following spring.

Figure 1. Calendar of Gypsy Moth activities.

From: http://www.ent.msu.edu/gypsyed/docs/lifecycle.html

Please note: This calendar was developed by researchers at Michigan State University. The time intervals indicated most likely apply to the particular climactic conditions for that region and some latitude must be given when applying this information to other areas.

Gypsy moth caterpillars are polyphagous and will feed on almost any tree or shrub depending on the population density and resulting competition (Liebhold, 1998; Liebhold et. al.,1998; Gypsy Moth: an informational guide, 2000). They have, however, displayed a preference for oaks and other hardwoods such as maples and elms (Liebhold; Gypsy Moth an informational guide) as well as willows, poplars, basswood, birch and fruit trees, especially apple (Klass). There are numerous reports of the gypsy moth's particular affinity for oaks (Baker; Liebhold; Gypsy Moth Ed. Program, M.S.U., 1997).


Tree Species at Risk for Gypsy Moth Defoliation
At Most Risk
 
 

Aspen (Populus
Apples and crabapples (Malus
Birches (Betula
Blue spruce (Picea
American beech (Fagus
Basswood (Tilia
Hawthorn (Crataegus
Hazelnut (Corylus
Oaks (Quercus
Poplar (Populus
Sweetgum (Liquidambar
Serviceberry (Amelanchier
Mountain ash (Sorbus
Witch hazel (Hamamelis
White pine (Pinus

Somewhat at Risk
 
 

Alder (Alnus
Balsam fir (Abies
Black walnut (Juglans
Butternut (Juglans
Cherry (Prunus
Eastern hemlock (Tsuga
Easter redbud (Cercis
Elm (Ulmus
Hickory (Carya
Hophornbeam (Ostrya
Hornbeam (Carpinus
Maples (Acer
Paw Paw (Asimina
Plum (Prunus
Sassafrass (Sassafrass
White and 
Norway Spruce (Picea

Minimal Risk
 
 

Arborvitae (Thuja
Ash (Fraxinus
Azalea (Azalea
Black locust (Robinia
Catalpa (Catalpa
Dogwood (Cornus
Eastern redcedar (Juniperus
Honey locust (Gleditzia
Horsechestnut (Aesculus
Lilac (Syringa
Rhododenron (Rhododendron
Tuliptree poplar (Liriodendron
Viburnum (Viburnum

Figure 2. Tree Species at Risk to Gypsy Moth Defoliation.

From: http://www.entm.purdue.edu/Entomology/ext/Moth/lifetabl.htm




Significant gypsy moth populations can result in varying levels of defoliation and defoliation may result in tree mortality. Many trees can survive a single defoliation depending on other additional, possibly synergistic factors. "If more than 60 percent of the canopy is consumed…, trees typically refoliate…; each refoliation stresses the tree, reducing its energy reserves." (Gypsy Moth Education Program, M.S.U.) Previously defoliated trees are more susceptible to disease, drought or other insects (Buss et. al.) as well as subsequent defoliations. This, in turn, may influence other forms of plant and animal life in the region (Millar, 2002). Some trees, apparently, may succumb to a single defoliation event.

"Tree mortality may result from one year's defoliation to hemlock, pine and spruce. Deciduous trees can normally withstand one year of defoliation, but two or more successive years may result in moderate to high mortality." (Hoover, 2000) On Long Island, the orange striped oak worm, a secondary defoliator, may attack certain refoliated trees later in the same growing season, thus greatly increasing the risk of stress and possible tree mortality (Wilkens and Vanderklein, 2002). Reports of defoliation and mortality abound (Baker; Gypsy Moth Ed. Prog., M.S.U.; ), and a number of individuals have also reported that such events occur in a regular cycle (Baker; Liebhold, 1998; Millar).
 
 

Figure 3. Areas frequently defoliated by gypsy moths, 1975-1994.

From: http://www.fs.fed.us/ne/morgantown/4557/gmoth/atlas/7594def.html




Purpose of the present study:

The purpose of this study was to involve a group of Longwood High School students in the collection, organization and analysis of data pertaining to the gypsy moth population in the Upton Ecological and Research Reserve (hereafter referred to as the "Upton Reserve"). The Upton Reserve is comprised of 530 acres located within the eastern portion of Brookhaven National Laboratory (B.N.L.) property, owned and operated by the U.S. Department of Energy (U.S.D.O.E.). It is also located within the "Core Preservation Area" of the Central Pine Barrens, Long Island, New York. Longwood High School is located just down the road from the lab, about one mile away. In November, 2000, the U.S.D.O.E. designated this property as protected habitat and entered into an agreement with the U.S. Fish and Wildlife Service (U.S.F.W.S.) to manage the property and to use it for educational and research activities (General Information on the Upton Ecological and Research Reserve).

The Long Island Pine Barrens constitutes one of only four such regions in the northeastern United States.

Figure 4. Pine Barrens ecosystems in the northeastern U.S.

From: http://www.pb.state.ny.us/maps_pdf/northeast.pdf






The Central Pine Barrens of Long Island consists of over 100,000 acres of

"…pitch pine and pine-oak forests, coastal plain ponds, marshes and streams. This region contains one of the greatest concentrations of endangered, threatened and special concern plant and animal species in New York, and provides deep flow recharge to the aquifer from which Long Island draws significant portions of its drinking water." (New York's Central Pine Barrens: Fact Sheet)

Figure 5. Long Island, New York Central Pine Barrens

From: http://www.pb.state.ny.us/maps_pdf/longis.pdf

Brookhaven National Laboratory constitutes about five percent of the Long Island Pine Barrens. There is little surface runoff or open water due to the general topography and porous soil (Natural Resources at B.N.L.). The Upton Reserve:

"…is a treasure trove of diversity, providing a home for more than 220 species of plants and 162 species of mammals, birds, reptiles and amphibians. Populations that are threatened or nonexistent elsewhere in New York State, such as tiger salamanders and hognosed snakes, appear to be thriving at B.N.L." (General Information on the Upton Ecological and Research Reserve) The Upton Reserve also contains the headwaters of the Peconic River. The dominant oak types in the Upton Reserve are a mix of scarlet and black oak species. They have been under attack by both gypsy moths and orange-striped oakworms (Wilkens and Vanderklein). In the summer of 2002, an aerial survey was conducted to document the extent of defoliation damage caused by both of these organisms.

Materials and Method

The protocol described by Liebhold et. al. in Gypsy Moth Egg Mass Sampling for Decision-Making, 1994, was followed. Twenty fixed-radius plots were randomly selected, with the intent of scattering them about the Upton Reserve property, as much as possible. Once the center of each plot was selected, a piece of rope, 18.6 feet in diameter was used to mark the perimeter with biodegradable tape. This radius yields a plot that is exactly 1/40th acre. Then all egg masses on trees with centers that fell within the perimeter of the plot were counted, along with any egg masses on any other objects within the confines of the plot. The overall percentage of new egg masses was determined by closely examining all those that were within reach. This was done by feeling each one as well as looking for exit holes and noting the coloration. "Current year egg masses have a good, buff, tan color and are hard and velvety to the touch; older ones are faded and soft to touch…" (Klass).
 
Characteristics useful for differentiating new vs. old egg masses.

Old Egg Masses New Egg Masses

soft to touch firm to touch

usually dull or bleached coloration usually darker beige

exit holes present no holes or small parasitoid exit holes present

Figure 6. Characteristics of new vs. old egg masses.

From: "Gypsy Moth Egg Mass Sampling for Decision-Making"

The overall percentage of new egg masses was determined by summing the counts from all twenty plots. This percentage was then applied to those egg masses that were out of reach, in order to determine final counts. Tree limbs and branches were examined from bottom to top, in a systematic way, with field glasses. This was done from several vantage points depending on the size of the tree.
 
 
 
 

Data and Calculations
 
 

Figure 7: Approximate location of the twenty sampling sites in the Upton Reserve






The following data were collected from the twenty sampling sites:
 
 
 
 
 
Sampling Date
Sampling Site 
Tree Tag Number
Ground Level Egg Masses (Old) 
Ground Level Egg Masses (New) 
Total Egg Masses (Crown)
*Egg Mass Density (number per acre) 
03/27/2003
I
EB7
6
9
24
722.9
03/27/2003
II
ED7
20
19
37
1319.4
03/29/2003
III
EN7
7
3
35
649.2
03/29/2003
IV
EK7
10
13
56
1366.7
03/29/2003
V
EF7
3
2
4
140.5
03/29/2003
VI
EG7
7
6
25
618.0
04/03/2003
VII
EV5
16
13
49
1260.9
04/03/2003
VIII
EC5
19
22
101
2407.1
04/03/2003
IX
ED5
6
8
56
1166.7
04/03/2003
X
EK5
8
4
14
371.7
04/03/2003
XI
EJ5
42
9
145
2552.4
04/24/2003
XII
EA1
0
0
2
30.2
04/24/2003
XIII
EB1
7
3
19
407.3
04/24/2003
XIV
EE1
10
9
5
435.6
04/24/2003
XV
EC1
10
5
15
426.8
04/24/2003
XVI
ED1
29
10
44
1065.3
04/24/2003
XVII
EF1
25
6
23
587.8
05/01/2003
XVIII
EM1
5
1
16
281.9
05/01/2003
XIX
EF5
0
0
0
0.0
05/01/2003
XX
EG1
4
4
14
371.7

 
 
 

Total number of new egg masses at ground level = 142

Total number of old egg masses at ground level = 234

Percent of total egg masses estimated to be new = 37.8%

* For each sampling site: estimated egg mass density per acre = [(percent of total egg

masses estimated to be new) x (total egg masses (crown)) + (ground level

egg masses(new)) ] x **40.

** Since each sampling site was 1/40th of an acre.
 
 

The following statistical data were determined using Microsoft Excel:
 
Mean
809.104
Standard Error
158.08319
Median
602.88
Mode
371.68
Standard Deviation
706.96952
Sample Variance
499805.91
Kurtosis
1.4353605
Skewness
1.3288859
Range
2552.4
Minimum
0
Maximum
2552.4
Sum
16182.08
Count
20

 
 
 
 
 
 
 
 
 
 
 

Discussion
 
 

In the "Gypsy Moth Egg Mass Sampling for Decision Making: A Users Guide," Liebold et.al. suggest that the study area should be between 10 and 500 acres. At 530 acres, the Upton Reserve did not seem to exceed that recommendation by enough to warrant subdividing it into smaller plots. Additionally, the methods outlined in this publication were primarily intended for making decisions about possible treatments, i.e., pesticide applications or other alternatives. Liebhold (2002) also recognizes the use of these methods for the study of population dynamics and many researchers have used egg mass counts for scientific purposes Andresen et. al., 2000; Kopchak, 2001).

Egg mass counts have traditionally been conducted during the late fall and winter, when leaves are off the trees. Long Island experienced an unusually harsh winter this past year and that, along with the logistics of transporting a group of high school students back and forth to the study area, which could be accessed only by unpaved roads, prevented us from conducting any sampling until late March and into early May. May 1st was the final sampling date. However, even on May 1st, the trunks and branches of trees were still clearly visible, and no significant leaf development had yet occurred. Additionally, there was no evidence that any gypsy moth larvae had emerged from the new egg masses. Weseloh (2003) conducted gypsy moth egg mass counts in April. It should also be noted that, although the egg mass counts for the twenty plots showed a high degree of variability, according to Liebhold et. al., that is exactly what should be expected when population densities are highest, and, "…side by side survey plots can contain vastly different numbers of egg masses."

The correlation between egg mass density and subsequent levels of defoliation varies, and, in fact, there are a number of variables that may ultimately determine the actual outcome. According to Liebhold et.al. (1994), egg mass densities of from 600 to 1000 per acre will result in approximately 30 to 45 % defoliation, but caution that there is a great deal of uncertainty in the relationship because "true" egg mass density and "true" defoliation are variable. Probyn (2003) equates defoliation with egg mass densities of 300 to 500 per acre, although she does not specify the extent of defoliation to be expected. Based on the predictions of Liebhold et. al. (1994), an approximately 40% defoliation level can be expected at the Upton Reserve. Also, since significant defoliation was observed there last summer, not once, but twice, this could mean a high degree of mortality for the trees that are there. The second defoliation last summer was at the hands (or, more correctly, the mouths) of the orange-striped oakworm (Wilkens and Vanderklein). "Expected mortality risks are generally considered high… in areas that have already been defoliated." (Kopchak)

There are a number of mitigating factors that may work on behalf of the trees, at least with regard to the gypsy moths. Researchers from Michigan State University and the USDA Forest Service have studied the relationship between egg mass hatching and microclimatic conditions like maximum and minimum temperatures and temperature variability. They found that egg masses with southern aspects, in two study areas in Michigan, had over 70% mortality and that egg masses on the bottom two meters of trees also experienced significant mortality rates (Andresen et. al; Probyn). This was attributed to higher temperatures within these egg masses in the fall due to solar loading. Gypsy moth caterpillars may also be killed by a number of disease organisms including fungi, bacteria, viruses and protozoans (Gypsy Moth in Southwest Michigan, 1999). The most significant of these, at high gypsy moth population densities, appear to be a nucleopolyhedrosis virus (NPV) and the fungus, Entomophaga maimaiga (Gypsy Moth in Southwest Michigan; Weseloh; USDA Forest Service Fact Sheet, 2003).

NPV is a disease that affects only gypsy moths and is naturally present in gypsy moth populations. When these populations are dense, epizootics may occur and are the most common reason for the collapse of these populations. Cadavers of caterpillars that succumb to NPV typically hang in an upside down V-shape and will liquefy and rapidly disintegrate (Gypsy Moth in Southwest Michigan; USDA Forest Service Fact Sheet). A commercially produced biological pesticide called "Gypcheck" makes use of NPV and is dispensed in limited quantities by some governmental agencies (Thorpe et. al.). Entomophaga maimaiga was introduced into the United States in 1910, but had little effect on gypsy moth populations until the late 1980's. "Since 1989, it has been widely released in states with gypsy moth populations." (Gypsy Moth in Southwest Michigan) Since 1992, numerous epizootics have been observed, but numerous constraints limit its use for pest control (USDA Forest Service Fact Sheet). The disease is spread by the fungal spores and the bodies of dead caterpillars appear dry, stiff and brittle (Gypsy Moth in Southwest Michigan).

Cool, rainy weather in the spring and early summer seems to favor the fungus (Weseloh; Gypsy Moth in Southwest Michigan). The six week period from May 1st through June 15th, 2003, has been one of the coolest and wettest ever, on Long Island.

Bacillus thuringiensis (BT), a naturally occurring, soil-dwelling bacterium, has also been used by government agencies to control gypsy moths. Unfortunately, it may also impact harmless butterflies and moths, some of which may be important pollinators. It is also only effective on young caterpillars with gut linings thin enough for the BT toxin to penetrate (Shetlar et. al.), so it must be used fairly soon after the larvae emerge from the egg masses. Chemical pesticides are also available, but all are toxic to other organisms including fish, bees, birds and aquatic invertebrates (Cornell Cooperative Extension Bulletin). They would not be suitable for use in the Upton Reserve. Gypsy moth sex pheromones have been used to trap males or disrupt mating behavior, but this is not very effective when population levels are high (Thorpe; Cornell Cooperative Extension Bulletin).
 
 

Summary and Conclusions

The gypsy moth population in the Upton Ecological and Research Reserve is significant. Many of the trees in the reserve suffered defoliation from the gypsy moth last May and June, and many of the oaks were defoliated a second time by the orange-striped oakworm, later in the summer. There is certainly cause for concern and significant tree mortality may occur. An egg mass density threshold of 250 egg masses per acre has been used elsewhere to justify treatment in both forest and residential areas (Liebhold et. al., 1994; Kopchak). The egg mass density in the Upton Reserve was more than double that number. Unfortunately, it is too late in the season or simply impractical for any kind of treatment at this time. It is hoped that the unusually cool, damp weather this spring will promote the spread of the fungus, Entomophaga maimaiga, and significant caterpillar mortality will result. Future studies should be conducted for the purpose of determining if the population is increasing or declining. According to Liebhold et. al.(1994), large numbers of old egg masses (greater than 50%) are indicative of a declining population. Hopefully, that is the case in the Upton Reserve, but more information should be gathered to support this hypothesis, as well as to aid in making decisions about possible future treatments.
 
 

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