United States

Department of

Agriculture

Forest

Service

Northern

Research Station

General Technical

Report NRS-37

Cost Analysis and 

Biological Ramifications for 

Implementing the Gypsy Moth 

Slow the Spread Program

Patrick C. Tobin
Abstract

The gypsy moth Slow the Spread Program is a joint U.S. Forest Service and state 

effort aimed at reducing the rate of gypsy moth, Lymantria dispar (L.) (Lepidoptera: 

Lymantriidae), spread into new areas in the United States. Between 2000 and 2007, 

federal funding for this program has ranged from $8 million to $10 million, with an 

additional 25 percent of funds contributed by participating states. Changes in funding 

levels can have important ramifications on the implementation of this Program, 

consequently affecting the rate of gypsy moth spread. This report presents a cost analysis 

for implementing the Slow the Spread Program across a range of funding levels, and 

predicts the consequent changes in gypsy moth spread rates. This work should be useful 

to program managers in implementing the Slow the Spread Program given yearly 

financial constraints and fluctuations, and also potentially serve as a template in the 

design of barrier zone management programs against other nonindigenous species.

Manuscript received for publication 13 August 2008

Published by:

USDA Forest Service

Northern Research Station

11 Campus Blvd., Suite 200

Newtown Square, PA 19073

December 2008

For additional copies:

USDA Forest Service

Publications Distribution

359 Main Road

Delaware, OH 43015

Fax: 740-368-0152

A and D: Future predictions of gypsy moth range 

expansion (yellow) under two finding levels 

(see Fig. 11).

B: Relationship between future gypsy moth 

spread rates and annual funding levels for 

STS (see Table 5).

C: Conceptual strategy for implementing 

STS with increased funding constraints by 

reducing the active management area (Action 

Zone) and increasing the area used in STS 

evaluation (Monitoring Area).

About the Author:

PATRICK TOBIN is a research 

entomologist with the U.S. Forest 

Service, Northern Research Station, 

Morgantown, WV.
United States

Department of

Agriculture

Forest

Service

Northern

Research Station

General Technical

Report NRS-37

Cost Analysis and 

Biological Ramifications for 

Implementing the Gypsy Moth 

Slow the Spread Program

Patrick C. Tobin

U.S. Department of Agriculture, Forest Service

Northern Research Station

11 Campus Blvd., Suite 200

Newtown Square, PA 19073

www.nrs.fs.fed.us
1

Introduction

The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae), was introduced 

outside of Boston, Massachusetts, in 1869 (Riley and Vasey 1870, Forbush and 

Fernald 1896). It has since slowly but relentlessly spread to the north, south, east, 

and west at variable rates, from 2.6 to 21.1 km/year (Tobin et al. 2007a), and is now 

established from Ontario to Virginia, and Nova Scotia to Wisconsin (Fig. 1). Gypsy 

moth larvae are highly polyphagous folivores that can exploit more than 300 host 

trees including species within the preferred host genera of Quercus, Larix, Populus, 

Salix, and Malus (Liebhold et al. 1995). Since 1890, a variety of management 

programs have been implemented to reduce its movement from generally infested 

areas (i.e., areas regulated under the gypsy moth quarantine; U.S. Code of Federal 

Regulations, Title 7, Chapter III, Section 301.45) to uninfested areas (e.g., Forbush 

and Fernald 1896, Burgess 1930, Perry 1955, Ravlin et al. 1987, Reardon et al. 1993, 

Sharov et al. 2002b, Tobin and Blackburn 2007). The Slow the Spread Program 

(STS) is a management strategy that uses a barrier zone located along the expanding 

gypsy moth population front, and is currently implemented across the states of 

Figure 1.—Portions of the United States and Canada considered generally infested 

by the gypsy moth (red area) and consequently regulated under a quarantine, 2008 

(U.S. Code of Federal Regulations, Title 7, Chapter III, Section 301.45 and Canadian 

Food Inspection Agency, Plant Health Division, Policy Directive D-98-09). The initial 

site of the gypsy moth introduction into North America (Medford, Massachusetts) is 

also shown.
2

North Carolina, Virginia, West Virginia, Kentucky, Ohio, Indiana, Illinois, Wisconsin, 

and Minnesota, encompassing nearly 40 million ha. Its primary goal is to reduce 

the rate at which the gypsy moth invades new areas. The delay in the future socioeconomic and environment impacts due to gypsy moth provides an approximate 4:1 

benefit-to-cost ratio (Leuschner et al. 1996).

The Slow the Spread Program

Under STS, extensive grids of pheromone-baited traps (>80,000 traps/year) are 

deployed to identify newly established gypsy moth populations ahead of the 

population front and estimate its yearly rate of spread. Management tactics target 

newly established populations, as colonies left unmanaged could persist, grow, 

and eventually coalesce with the moving population front. This increases the rate 

of spread through a process known as stratified dispersal, which results from both 

local growth and dispersal coupled with stochastic, long-distance jumps through 

anthropogenic or atmospheric transport mechanisms (Fig. 2; Hengeveld 1989, Andow 

et al. 1990, Shigesada and Kawasaki 1997). Higher management priorities are placed 

upon those colonies that are thought to most affect gypsy moth spread rates, such as 

higher density colonies located farthest from the generally infested area (Sharov et al. 

2002b, Tobin et al. 2004, Tobin and Blackburn 2007).

Figure 2.—Hypothetical range expansion of an invading species from initial time t to 

t+n when spread proceeds by local growth and dispersal (a) or stratified dispersal (b). 

Long distance jumps can have profound ramifications in the rate at which an invader 

spreads into new areas.
3

The Slow the Spread Program area is divided into two zones: (1) an Evaluation 

Zone that is located proximal to the gypsy moth generally infested area, and (2) an 

Action Zone that is located distally (Fig. 3; Tobin et al. 2004). From 2000-2006, 

the extent of the Evaluation and Action zones were approximately 70 and 100 km 

wide, respectively (Fig. 3). The width of both zones were based upon prior research 

demonstrating that most new gypsy moth colonies arise within these distances from 

the generally infested area (Sharov and Liebhold 1998).

Pheromone-baited traps are deployed in both the Evaluation and Action Zones, 

but at different trap grid intensities (Fig. 3; Tobin et al. 2004). In the Evaluation Zone, 

traps are set 3 to 8 km apart, while in the Action Zone, traps are approximately 2 km 

apart. Higher gypsy moth densities, such as those within the Evaluation Zone, require 

less spatial resolution in trap deployment because gypsy moth populations tend to be 

highly spatially autocorrelated (Sharov et al. 1996). Therefore, gypsy moth densities 

at unsampled locations can be estimated through geostatistical methods (Isaaks and 

Srivastava 1989). In contrast, in the Action Zone, gypsy moth populations are rarer, 

lower in abundance, and consequently less spatially autocorrelated; thus, to detect 

newly established populations in this area, a greater trap resolution is needed 

Figure 3.—The STS Program Area in 2007, showing the locations of the Action 

Zone (grey area) and Evaluation Zone (orange and yellow areas). The map of West 

Virginia presents an example of the different trap grid densities (pheromone-baited 

traps represented as small black dots) used in STS.
4

(Sharov et al. 1998). The Action Zone is also where active management is 

implemented (i.e., the elimination of low-density gypsy moth populations). In 

response to the initial detection of a newly established population in the Action Zone, 

the area is generally delimited through more extensive trapping, using traps set 500 to 

1000 m apart, to better define the density and spatial extent of the newly established 

population (Sharov et al. 2002b, Tobin et al. 2004). Also, following a treatment 

against the population, delimiting trapping will be used to evaluate the effectiveness 

of the treatment (Sharov et al. 2002a, Tobin and Blackburn 2007). Different trap 

grid densities in the Evaluation and Action Zones were previously optimized for 

use in detection (Sharov et al. 1996), treatment evaluation (Sharov et al. 2002a), 

and in the estimation of gypsy moth spread (Sharov et al. 1995). An example of the 

management process of the Slow the Spread Program is presented in Figure 4.

Georeferenced trap catch data from the Evaluation Zone are used to estimate 

gypsy moth abundance and to delineate various gypsy moth population boundaries. 

The spatial location at which 1, 3, 10, 30, 100, or 300 male moths are expected to 

be trapped per trapping area is estimated (Sharov et al. 1995), and the mean spatial 

displacement between these gypsy moth population boundaries in successive years 

is calculated to estimate gypsy moth spread (Sharov et al. 1997, Tobin et al. 2007a). 

Annual rates of spread are then used to evaluate STS, and to adjust the boundaries of 

the Evaluation and Action Zones in response to gypsy moth range expansion.

The primary costs associated with STS are from treatment applications, traps 

and trap deployments, and fixed costs (i.e., personnel and database management). 

Several treatment options are used against different population densities and at 

different doses and/or number of applications, all of which affect the cost. There are 

also several technical considerations when implementing any management program 

such as STS across such broad geographical scales. Since the variable costs in STS 

are treatment and trap costs, altering the scale of STS (i.e., increasing or decreasing 

the width of the Action and/or Evaluation Zones) would affect its overall cost. In this 

analysis, I used 2000-2006 budget data for STS to decompose the costs associated 

with various trap grid densities and treatments. I then combined these costs with fixed 

costs to determine the extent over which STS can be implemented across a range of 

funding levels. This report should provide a template for federal and state program 

managers to make informed decisions as to how to coordinate STS given financial 

constraints. Finally, I estimated the biological ramifications, in terms of gypsy moth 

spread rates, based upon various implementation scenarios.
5

Figure 4.—Gypsy moth monitoring under STS in 2005 for a selected area, showing 

the spatial interpolation of trap catch data, estimated locations of gypsy moth 

population boundaries (3, 10, 30, and 100 moths per trap), and the boundary 

between the Action and Evaluation Zones (a).The trap catch data (represented as 

dots) from the ‘hot spot’ is shown in the prior year (b). The dark grey area represents 

an implemented treatment targeting the population in 2005 (c), and the trap catch 

data from 2006 reveal a substantially reduced population (d).
6

Methods

Treatment Costs in the Slow the Spread Program

Treatment data from 2000 to 2006 were used to estimate costs for each treatment 

tactic used in STS. The primary treatment option is mating disruption. Plastic flakes 

impregnated with synthetic pheromone (Disrupt® II, Hercon® Environmental, 

Emigsville, PA) are applied aerially to foliage, flooding the air with pheromone and 

consequently interfering with the male moth’s ability to locate females for mating 

(Thorpe et al. 2006). Other options are the biopesticide Bacillus thuringiensis variety 

kurstaki (Reardon et al. 1994), the insect growth regulator diflubenzuron (registered 

as Dimilin®) (U.S. Dep. Agric. 1995), and the gypsy moth nucleopolyhedrosis virus 

(registered as Gypchek®) (Reardon et al. 1996). Only those treatment tactics that 

were analyzed and were part of the record of decisions under the gypsy moth Final 

Environmental Impact Statement (U.S. Dep. Agric. 1995) can be used in STS.

Treatment tactics vary according to the density of the targeted population. 

Mating disruption is more effective in low-density populations that tend to be farther 

from the generally infested area, while B. thuringiensis kurstaki is more effective 

against high-density populations that tend to be closer to the generally infested area 

(Tobin and Blackburn 2007). Mean pretreatment moth density in areas treated using 

mating disruption (2000-2006) was 4.7 moths per trap (SE=0.3). Mating disruption 

is rarely used in areas where moth densities exceed 10 moths per trap (90 percent of 

the treatment blocks had pretreatment moth densities < 10), or when alternate life 

stages are found (i.e., egg masses). In contrast, mean pretreatment moth densities 

in areas treated with B. thuringiensis kurstaki was 17.5 moths per trap (SE=2.0). To 

account for the differences in the location of various treatment tactics, the proportion 

of acreage treated with each tactic and dose, across all years, was calculated based 

upon the location of the tactic relative to the beginning of the Action Zone (i.e., 

the boundary separating the Action and Evaluation Zones, cf. Fig. 3). Nonlinear 

regression (PROC NLIN, SAS Institute 1999) was used to fit an exponential model to 

each tactic and dose according to

(1)

where P is the proportion of treated acreage, D is the distance (km) from the 

beginning of the Action Zone, and r and B are parameters representing the rate of 

decrease and lag, respectively (Brown and Mayer 1988). This function was then used 

to estimate the mean acreage treated, per tactic and dose, at a given distance from 

the beginning of the Action Zone. Mean treated acreage was then combined with 

treatment costs to determine the average annual treatment costs given the overall 

width of the Action Zone implemented under STS.

P =

(–rD+B) 1 + e

1 ,

( )
7

Trapping Costs in the Slow the Spread Program 

I measured the trap grid density within the implemented Action and Evaluation 

Zones, and then related the trapping costs as a function of the distance from the 

Action and Evaluation Zone common boundary. A uniform cost per trap of $48 was 

used, which reflects the average cost per trap (excluding fixed costs associated with 

trapping, i.e., personnel salaries and fringe benefits) across all participating states 

from 2000 to 2006. Linear regression (PROG GLM, SAS Institute 1999) was used to 

estimate the total costs for trapping as a function of the distance from the Action and 

Evaluation Zone common boundary. Trap costs were then used to estimate Programwide costs given the combined widths of the Action and Evaluation Zones.

Fixed Costs in the Slow the Spread Program 

The fixed costs associated with STS are listed in Table 1. They include state and 

federal personnel costs, travel, database management including web support (e.g., 

www.gmsts.org), financial management services in support of the STS Foundation, 

Program-wide aerial applicator contracts, and work in support of National 

Environmental Policy Act (NEPA) compliance for gypsy moth management on 

federally owned lands. I used data from 2005 and 2006 to ensure that fixed costs were 

expressed in the most current dollars. Future increases in fixed costs due to inflation 

were not considered. Increases in the efficiency of STS due to advances in research 

and development, which could reduce costs, also were not considered.

Year

Budget Category 2005 2006

State costs 

 (personnel salaries, fringe, and travel) 1,171 (46.9%) 1,400 (53.1%)

Financial management services 30 (1.2%) 30 (1.1%)

Forest service costs 

 (personnel salaries, fringe, and travel) 140 (5.6%) 140 (5.3%)

Mating disruption application contract 15 (0.6%) 15 (0.6%)

NEPA 25 (1.0%) 25 (0.9%)

Database management 846 (33.9%) 759 (28.8%)

APHIS-Regulatory 270 (10.8%) 270 (10.2%)

TOTAL 2,497 (100%) 2,639 (100%)

Table 1.—Summary of recent fixed costs for STS, in thousands $USD (percentages 

in parentheses)
8

Program Implementation and Gypsy Moth Spread 

The annual rate of gypsy moth spread is based upon the mean year-to-year spatial 

displacement across all gypsy moth population boundaries (i.e., the 1, 3, 10, 30, 

100, and 300 moths per trap boundaries; Sharov et al. 1995, Tobin and Blackburn 

2007, Tobin et al. 2007a). I used annual gypsy moth spread rate data from 2000 to 

2006 to estimate 3-year moving averages of spread (i.e., 2000-2002, 2001-2003, ..., 

2004-2006) (Table 2). These spread rates do not reflect regional or state differences 

in spread previously reported (Sharov et al. 1999, Tobin and Whitmire 2005, 

Tobin et al. 2007a and b), but instead reflect overall spread rates under the current 

implementation of STS.

Previously, Liebhold et al. (1992) estimated gypsy moth spread at 21.7 

km/year (in the absence of STS or any other management program). Sharov et al. 

(1998) derived a theoretical estimate of gypsy moth spread (17 km/year) using a 

model parameterized from gypsy moth demographic data, also in the absence of a 

management program. These values, coupled with 3-year moving averages of spread 

observed during the implementation of STS, were used to predict the relationship 

between levels of management activity (as denoted by the width of the Action Zone 

over which treatments are deployed) and projected rates of gypsy moth spread. 

These projected rates were then extrapolated to demonstrate the impact of long-term 

management activity on the expected gypsy moth range 20 years into the future.

Table 2.—Gypsy moth spread rates under STS, based upon the yearly displacement 

of male moth population boundaries

3-Year moving average

Year Spread rate (km/year) of spread rate (km/year)

2000 –4.0 6.0

2001 13.8 9.7

2002 –0.4 3.1

2003 12.6 8.6

2004 –9.8 0.8

2005 4.8 2.5

2006 6.7 0.6
9

Results

Treatment Costs

A summary of the use of treatment options available in STS and their respective costs 

is listed in Table 3. The relationship between the proportion of acres treated by each 

treatment tactic as a function of the distance from the beginning of the Action Zone 

is shown in Figure 5. Depending on the extent of STS, especially the width of the 

Action Zone over which the majority of treatments are deployed, treatment costs will 

vary nonlinearly (Fig. 5). Nonlinear parameter estimates for each treatment tactic 

function are listed in Table 4.

Trapping Costs

The mean overall cost for trapping within the Evaluation Zone is $28,138 for each 

5 km of width. Costs in the Evaluation Zone are fairly stable within 50 km of the 

boundary between the Action and Evaluation Zones, and then the costs begin to 

decline as the intertrap distance changes from 3 to 5 to 8 km (Fig. 6b and d). A piecewise linear regression model was fit to this relationship to account for these different 

trapping costs. In the Action Zone, trapping costs decline linearly as the distance from 

the beginning of the Action Zone increases (Fig. 6a and c). The intertrap distance of 

traps (approximately 2 km) within the Action Zone is fairly standardized; however, 

because more new gypsy moth colonies occur closer to the generally infested area, 

there are consequently more traps set near the beginning of the Action Zone (Fig. 6a) 

due to the use of pre- and post-treatment trapping delimits in which traps are set 500 

to 1000 m apart. As a reference, the overall mean trapping cost for each 5 km width 

of Action Zone is $152,000.

Table 3.—Summary of treatment options and their use in STS

Dose/acre × number Average acres

Treatment option of applicationsa Cost/acre treated/year

B. thuringiensis kurstaki 24 BIU × 1 $22.00 10,062

24 BIU × 2 $44.00 68,984

30 BIU × 1 $22.00 422

30 BIU × 2 $44.00 1,988

38 BIU × 1 $28.00 8,729

Mating disruption 6 g × 1 $8.34 273,741

15 g × 1 $13.73 145,532

Dimilin® 1 oz × 1 $20.00 3,258

Gypchek® 5×1011 PIB × 1 $20.00 5,941

a

BIU, billion international units. PIB, polyhedral inclusion bodies.
10

Table 4.—Nonlinear regression parameter estimates (cf. Eq. 1) for the relationship 

between acres treated and distance from the beginning of the Action Zone

a

BIU, billion international units. PIB, polyhedral inclusion bodies.

Parameter Estimates (SE)

Dose/acre × number

Treatment Option of applicationsa Rate (r) Lag (B)

B. thuringiensis kurstaki 24 BIU × 1 0.1478 (0.0195) 0.2301 (0.1295)

24 BIU × 2 0.0704 (0.0010) 1.7203 (0.0258)

30 BIU × 1 1.2586 (0.3673) –11.2081 (3.3255)

30 BIU × 2 0.1400 (0.0089) 1.4774 (0.1190)

38 BIU × 1 0.1432 (0.0320) 2.9736 (0.6453)

Mating disruption 6 g × 1 0.0654 (0.0010) 2.1729 (0.0338)

15 g × 1 0.0644 (0.0015) 1.3055 (0.0365)

Dimilin® 1 oz × 1 0.0753 (0.0106) 2.1292 (0.3182)

Gypchek® 5×1011 PIB × 1 0.0770 (0.0068) 0.7015 (0.0860)

Figure 5.—Nonlinear relationships between the proportion of acres treated by 

each treatment tactic as a function of the distance from the beginning of the Action 

Zone (a-c). The utility of these relationships, using B. thuringiensis kurstaki (red; 

24 BIU/acre × 1 application) and mating disruption (blue; 6 g/acre) are shown as 

examples (d). On average, half of the treated acreage for B. thuringiensis kurstaki

(red dotted line) and mating disruption (blue dotted line) occurs within 2 and 33.2 km, 

respectively, of the beginning of the Action Zone. Btk, B. thuringiensis kurstaki; 

MD, Mating disruption.
11

Figure 6.—Relationship between the number of traps deployed (a, b) and 

corresponding costs (c, d) for the Action and Evaluation Zones relative to the 

distance from the Action Zone/Evaluation Zone common boundary. Linear regression 

equations for the trap costs: (c) Predicted costs = –1.50(Distance) + 237.95; 

(d) Predicted costs = 29.92 and Predicted costs = –0.81(Distance) + 72.43.

Program Implementation and Gypsy Moth Spread 

The combination of trapping and treatment costs, and the manner in which they 

are deployed, can be used to determine the extent that STS can be implemented at 

a given funding level. In this report, the assumption was made that annual budgets 

are more likely to decrease rather than increase. To examine the effect of increased 

financial constraints, I explored the feasibility of reducing the widths of the Action 

and Evaluation Zones.

Trap catch data from the Evaluation Zone are used primarily to estimate annual 

spread (Fig. 7), and this information is not trivial. The primary goal of the Slow the 

Spread Program is to slow the rate at which gypsy moth invades new areas. The 

displacement in moth population boundaries is used to estimate annual spread rates 

and thus is critically important in determining if the goals of STS are being achieved. 
12

It becomes infeasible to eliminate or drastically reduce the width of the Evaluation 

Zone without jeopardizing the ability to estimate spread. Moreover, even if the 

Evaluation Zone were to be reduced in width, the Program costs would not greatly 

change since few treatments are deployed here (Fig. 5) and trap costs are minimal 

relative to other costs in the Program (Fig. 6). 

The overall width of STS (Action and Evaluation Zones) would thus need 

to be maintained, at least in the near future, at roughly 170 km to estimate annual 

gypsy moth spread rates and to identify newly established populations ahead of the 

generally infested area. Trap grid densities are already optimized for detecting new 

colonies and estimating spread; thus, reducing the intensity of trapping deployments 

would be counterproductive. The primary, most biologically feasible manner by 

which STS could be implemented with budgetary constraints would be to decrease 

the width of the Action Zone (essentially reducing treatments) and increase the width 

of the Evaluation Zone (Fig. 8). This results in savings in both trapping (since trap 

grid density would be reduced) and treatment costs. An example of how treatments 

would be reduced with a corresponding reduction in Action Zone width is shown 

in Figure 9. Since gypsy moth spread occurs through stratified dispersal, the goal 

Figure 7.—Mean (±SD) locations of the 1, 3, 10, 30, 100, and 300 moth population 

boundaries (Sharov et al. 1997) relative to the common boundary of the Action 

and Evaluation Zones. All but the 1 moth/trap boundary are estimated using traps 

deployed in the Evaluation Zone.
13

Figure 8.—Implementing STS with increased financial constraints.

Figure 9.—Hypothetical example of the effects of a reduced Action Zone width on 

treatment acreage. The cumulative percentage of all acreage treated under STS (red 

curve) is shown across the length of the Action Zone. The top graph is the current 

implementation design, and the bottom graph illustrates the loss in treatment acreage 

(red area) when the Action Zone width is reduced by X km. This strategy ensures that 

the most distal colonies are still targeted for elimination since they would be the ones 

most likely to contribute to increased rates of spread under stratified diffusion.
14

of slowing its spread can still be achieved, albeit to varying levels of success, when 

the Action Zone is reduced in width providing that the most distal colonies are still 

targeted for treatment. However, since fewer colonies would be targeted, the rate of 

gypsy moth spread would increase because colonies left unmanaged would contribute 

to gypsy moth spread.

Using gypsy moth spread rate data observed during the current implementation 

of STS (Table 2) and data in the absence of STS (Liebhold et al. 1992, Sharov et al. 

1998), linear regression was used to predict spread rates across varying widths of 

the Action Zone (Fig. 10). This relationship is challenging to predict given the lack 

of empirical or theoretical data on spread between the two extremes (i.e., a 100-kmwide Action Zone under STS, and no STS), but still the only empirical approach 

currently available to estimate the impact of reduced funding on spread. Moreover, 

it is still reasonable to assume that gypsy moth spread rates with some reduced level 

of STS would likely be between those spread rates observed in the absence of and 

in the presence of STS as currently implemented. In the event that future financial 

constraints force the Action Zone to be reduced, then spread rate data can be used to 

enhance the predictions displayed in Figure 10.

Figure 10.—Mean gypsy moth spread rates under current STS operating procedures 

(diamonds) coupled with spread in the absence of STS (circles; Liebhold et al. 1992, 

Sharov et al. 1998). Linear regression was fit (solid line; 95% CI as dashed lines) to 

these data to extrapolate the expected rate of spread over a range of Action Zone 

widths.
15

Table 5.—Costs in millions $USD and projected gypsy moth spread rates associated 

with the implementation of STS. Percent of the total program cost allocated to 

trapping, treatment, and fixed costs are noted in parentheses.

Width of zones (km)

 Projected gypsy

Action Evaluation Trapping costs Total moth spread

Zone Zone Fixed Treatment program rate, km/yr

(AZ) (EZ) AZa EZb Total (%) costs (%)c costs (%)d coste (±95% CI)f

100 70 $3.34 $0.39 $3.73 (28.7) $2.30 (17.7) $6.98 (53.7) $13.01 4.9 (2.2–7.7)

95 75 $3.11 $0.40 $3.51 (28.3) $2.30 (18.5) $6.61 (53.2) $12.42 5.7 (2.9–8.4)

90 80 $2.89 $0.42 $3.31 (28.2) $2.30 (19.6) $6.15 (52.3) $11.75 6.4 (3.7–9.1)

85 85 $2.67 $0.43 $3.11 (28.2) $2.30 (20.9) $5.61 (50.9) $11.02 7.1 (4.4–9.8)

80 90 $2.47 $0.45 $2.91 (28.5) $2.30 (22.5) $5.00 (48.9) $10.22 7.8 (5.1–10.6)

75 95 $2.27 $0.46 $2.73 (29.1) $2.30 (24.5) $4.36 (46.4) $9.39 8.6 (5.8–11.3)

70 100 $2.07 $0.48 $2.55 (29.8) $2.30 (26.9) $3.70 (43.3) $8.55 9.3 (6.6–12.0)

65 105 $1.89 $0.49 $2.38 (30.7) $2.30 (29.7) $3.07 (39.6) $7.75 10.0 (7.3–12.7)

60 110 $1.71 $0.51 $2.22 (31.7) $2.30 (32.9) $2.48 (35.4) $7.00 10.7 (8.0–13.5)

55 115 $1.54 $0.53 $2.06 (32.5) $2.30 (36.3) $1.96 (31.0) $6.33 11.5 (8.7–14.2)

50 120 $1.38 $0.54 $1.92 (33.4) $2.30 (40.1) $1.52 (26.5) $5.74 12.2 (9.5–14.9)

45 125 $1.22 $0.56 $1.78 (34.0) $2.30 (43.9) $1.16 (22.1) $5.24 12.9 (10.2–15.6)

40 130 $1.07 $0.57 $1.64 (34.0) $2.30 (47.7) $0.87 (18.0) $4.82 13.6 (10.9–16.4)

a

Average cost/5km of Action Zone based on $48/trap, and a linear function of trap density over width (Fig. 6).

b

Average cost/5 km Evaluation Area based on $48/trap, and a linear function of trap density over width (Fig. 6).

c

Fixed costs include fulltime salaries and fringe, travel, audit and management services, database management, 

and NEPA and regulatory costs (Table 1).

d

Estimated by a cost function using yearly treatment data from 2001-2006 (Table 3, Fig. 5).

e

Total assumes 75% federal contribution + 25% participating state contribution.

f

Interpolated from relationship presented in Figure 10.

A combination of all treatment, trapping, and fixed costs across a range of 

widths for the Action and Evaluation Zones is presented in Table 5. The projected 

gypsy moth spread rates are also listed in Table 5. The total width of STS is constant, 

with the primary change being the gradual shift of area from the Action Zone into 

the Evaluation Zone (cf. Fig. 8). Costs in the Evaluation Zone are almost exclusively 

related to trapping costs, which are proportionally inexpensive. For example, a 

70-km-wide Evaluation Zone would cost $390,000 to implement, while a 130-kmwide Evaluation Zone would cost $570,000. In contrast, corresponding changes in 

the Action Zone would decrease the costs from $3.3 million (under a 100-km-wide 

Action Zone) to $1.1 million (under a 40-km-wide Action Zone, Table 5). Using 

the estimated rates of gypsy moth spread across selected funding levels, I predicted 

long-term impacts on gypsy moth range expansion by determining the increase in the 

gypsy moth quarantined area from 2006 to 2025 (Fig. 11).

In this report, I presented an overview of the costs associated with STS and 

the biological ramifications of maintaining or modifying its extent. There are several 

additional points that could affect gypsy moth spread but are not easy to quantify. 
16

Figure 11.—Projections of gypsy moth range expansion over the next 20 years 

(2006-2025) at selected levels of STS funding.

First, STS is only one management program targeting gypsy moth. Others include 

cooperative suppression programs that operate within the generally infested area 

(Fig. 1) to mitigate gypsy moth outbreaks. The absence of gypsy moth suppression 

programs could affect gypsy moth spread since new gypsy moth introductions seem 

to be more frequent following outbreaks in source areas (Myers and Rothman 1995).

It is uncertain how potential future higher rates of gypsy moth spread, possibly 

resulting from a reduction in the extent of STS, will affect the degree of “boundary 

compression.” This phenomenon has been demonstrated both theoretically (Sharov et 

al. 1996) and empirically (Tobin and Whitmire 2005). Sharov et al. (1996) described 
17

a model of gypsy moth spread that predicts when spread was reduced, the distance 

between moth population boundaries (i.e., boundaries representing low, intermediate, 

and high density populations) were likewise reduced or “compressed.” If moth 

population boundaries become less compressed due to higher spread rates, it is not 

clear what effect this could have on the ability to accurately estimate moth population 

boundaries, even within a wider Evaluation Zone. This could hinder the Program’s 

ability to accurately measure the rate of gypsy moth spread. 

It is also unclear if reduced boundary compression would affect the abundance 

of natural enemies, such as the gypsy moth entomopathogens Entomophaga 

maimaiga (Hajek 1999) and the nucleopolyhedrosis virus (LdMNPV) (Elkinton 

and Liebhold 1990), and their regulation of gypsy moth populations. It is possible 

that when higher density populations are in closer proximity to intermediate 

density populations, then entomopathogens, especially E. maimaiga, could disperse 

from high gypsy moth population density areas and exert population control in 

intermediate density populations. In fact, any additional regulatory mechanism, 

whether through biological control agents or cooperative suppression programs, that 

operates within or near STS likely has some positive synergistic effect on the efficacy 

of STS.

Lastly, increased rates of gypsy moth spread will increase the rate at which 

new counties become regulated under the gypsy moth quarantine (U.S. Code of 

Federal Regulations, Title 7, Chapter III, Section 301.45). The movement of goods, 

including nursery stock and personal household items, from a quarantined area to 

an unquarantined area is regulated. Specifically, commercial products are required 

to obtain compliance prior to the movement of goods through interstate or intrastate 

commerce. This regulation obviously comes at a cost. An economic benefit of STS 

is to delay the costs associated with maintaining the quarantine (Sills and Bigsby 

2007), as well as delaying the costs associated with gypsy moth outbreaks (Leuschner 

et al. 1996). Thus, reducing the implemented area of STS will have future additional 

management and regulatory costs that could eliminate any savings gained through 

budget reductions.
18

Summary

The gypsy moth invasion in the United States proceeds through a process known as 

stratified dispersal. Local growth and dispersal are coupled with long-range, spatially 

disjunct “jumps” in the population (Hengeveld 1989, Andow et al. 1990, Shigesada 

and Kawasaki 1997). Newly founded populations can greatly contribute to the rate of 

gypsy moth spread when they grow and coalesce with the expanding population front 

(Fig. 2). The STS Program is implemented along the leading edge of the population 

front to identify and eliminate these new populations formed by these “jumps” before 

they contribute to the rate of spread (Tobin and Blackburn 2007). Future budgetary 

constrains could force STS managers at the state and federal levels to modify the 

relative widths of the Action and Evaluation Zones (Table 5), and hence the degree to 

which new populations can be managed. The less the gypsy moth is managed under 

STS, the greater the estimated rate of gypsy moth spread (Fig. 10) and the greater the 

rate at which the gypsy moth quarantined area is increased (Fig. 11).

The rationale behind STS could be applied in the development and 

implementation of other invasive species management programs. Any species that 

spreads according to stratified dispersal and does not yet fully occupy its susceptible 

host range could benefit from such a program, assuming that (1) there is a method for 

detecting low-density populations, which are more feasible to eradicate than higher 

density populations; (2) effective treatment tactics exist; and (3) the benefits of the 

program outweigh the costs. For example, there is currently an interest in developing 

a similar management program for the emerald ash borer, Agrilus planipennis

Fairmaire (Coleoptera: Buprestidae). Such an effort will undoubtedly incur many of 

the same types of costs reported here, and likewise would face parallel logistic and 

biological constraints. Consequently, costs and biological analyses from STS could 

serve as a valuable template when designing programs to reduce the spread of other 

nonindigenous species.

Acknowledgments

I thank Laura Blackburn, Melody Keena, John Kyhl, Sandy Liebhold, Donna 

Leonard, Rick Turcotte, and Susan Wright (USDA Forest Service); Andy Roberts 

(Virginia Tech University); and Kevin Thorpe (USDA Agricultural Research Service, 

retired) for their valuable assistance and comments during the preparation of this 

report.
19

Literature Cited

Andow, D.A.; Kareiva, P.M.; Levin, S.A.; Okubo, A. 1990. Spread of invading 

organisms. Landscape Ecology. 4: 177-188.

Brown, R.F.; Mayer, D.G. 1988. Representing cumulative germination. 2. The use 

of the Weibull function and other empirically derived curves. Annals of 

Botany. 61: 127-138.

Burgess, A.F. 1930. The gipsy [sic] moth and the brown-tail moth. Farm. Bull. 

1623. Washington, DC: U.S. Department of Agriculture.

Elkinton, J.S.; Liebhold, A.M. 1990. Population dynamics of gypsy moth in North 

America. Annual Review of Entomology. 35: 571-596.

Forbush, E.H.; Fernald, C.H. 1896. The gypsy moth. Boston, MA: Wright and Potter 

Printing Co.

Hajek, A.E. 1999. Pathology and epizootiology of Entomophaga maimaiga

infections in forest Lepidoptera. Microbiology and Molecular Biology 

Reviews. 63: 814-835.

Hengeveld, R. 1989. Dynamics of biological invasions. London: Chapman and Hall. 

160 p.

Isaaks, E.H.; Srivastava, R.M. 1989. An introduction to applied geostatistics. New 

York: Oxford University Press. 561 p.

Leuschner, W.A.; Young, J.A.; Waldon, S.A.; Ravlin, F.W. 1996. Potential benefits 

of slowing the gypsy moth’s spread. Southern Journal of Applied Forestry. 

20: 65-73.

Liebhold, A.M.; Gottschalk, K.W.; Muzika, R.M.; Montgomery, M.E.; Young, R.; 

O’Day, K.; Kelley, B. 1995. Suitability of North American tree species to the 

gypsy moth: a summary of field and laboratory tests. Gen. Tech. Rep. NE211. Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern 

Research Station. 34 p.

Liebhold, A.M.; Halverson, J.A.; Elmes, G.A. 1992. Gypsy moth invasion in North 

America: a quantitative analysis. Journal of Biogeography. 19: 513-520.

Myers, J.H.; Rothman, L.D. 1995. Field experiments to study regulation of 

fluctuating populations. In: Cappuccino, N.; Price, P.W., eds. Population 

dynamics: New approaches and synthesis. San Diego, CA: Academic Press: 

229-250.

Perry, C.C. 1955. Gypsy moth appraisal program and proposed plan to prevent 

spread of the moths. Tech. Bull. 1124. Washington, DC: U.S. Department of 

Agriculture.
20

Ravlin, F.W.; Bellinger, R.G.; Roberts, E.A. 1987. Status of gypsy moth 

management programs in the United States: status, evaluation, and 

recommendations. Bulletin of the Entomological Society of America. 33: 

90-98.

Reardon, R.; Dubois, N.; McLane, W. 1994. Bacillus thuringiensis for managing 

gypsy moth: a review. FHM-NC-01-94. Radnor, PA: U.S. Department of 

Agriculture, Forest Service, National Center of Forest Health Management. 

32 p.

Reardon, R.C.; Podgwaite, J.; Zerillo, R. 1996. Gypchek – the gypsy moth 

nucleopolyhedrosis virus product. FHTET-96-16. Radnor, PA: U.S. 

Department of Agriculture, Forest Service, Forest Health Technology 

Enterprise Team. 33 p.

Reardon, R.; Venables, L.; Roberts, A. 1993. The Maryland integrated pest 

management gypsy moth project 1983-1987. NA-TP-07-93. Radnor, PA: 

U.S. Department of Agriculture, Forest Service, Northeastern Area, State and 

Private Forestry. 35 p.

Riley, C.V.; Vasey, G. 1870. Imported insects and native American insects. 

American Entomologist. 2: 110-112.

SAS Institute. 1999. SAS/STAT® User’s Guide, Version 8. Cary, NC. 3809 p.

Sharov, A.A.; Leonard, D.S.; Liebhold, A.M.; Clemens, N.S. 2002a. Evaluation of 

preventive treatments in low-density gypsy moth populations. Journal of 

Economic Entomology. 95: 1205-1215.

Sharov, A.A.; Leonard, D.S.; Liebhold, A.M.; Roberts, E.A.; Dickerson, W. 2002b. 

Slow the Spread: a national program to contain the gypsy moth. Journal of 

Forestry. 100: 30-35.

Sharov, A.A.; Liebhold, A.M. 1998. Model of slowing the spread of gypsy moth 

(Lepidoptera: Lymantriidae) with a barrier zone. Ecological Applications. 

8: 1170-1179.

Sharov, A.A.; Liebhold, A.M.; Roberts, E.A. 1996. Spatial variation among counts 

of gypsy moths (Lepidoptera: Lymantriidae) in pheromone-baited traps at 

expanding population fronts. Environmental Entomology. 25: 1312-1320.

Sharov, A.A.; Liebhold, A.M.; Roberts, E.A. 1997. Methods for monitoring the 

spread of gypsy moth (Lepidoptera: Lymantriidae) populations in the 

Appalachian mountains. Journal of Economic Entomology. 90: 1259-1266.

Sharov, A.A.; Liebhold, A.M.; Roberts, E.A. 1998. Optimizing the use of barrier 

zones to slow the spread of gypsy moth (Lepidoptera: Lymantriidae) in 

North America. Journal of Economic Entomology. 91: 165-174.
21

Sharov, A.A.; Pijanowski, B.C.; Liebhold, A.M.; Gage, S.H. 1999. What affects 

the rate of gypsy moth (Lepidoptera: Lymantriidae) spread: winter 

temperature or forest susceptibility? Agricultural and Forest Entomology. 

1: 37-45.

Sharov, A.A.; Roberts, E.A.; Liebhold, A.M.; Ravlin, F.W. 1995. Gypsy moth 

(Lepidoptera: Lymantriidae) spread in the central Appalachians: three 

methods for species boundary estimation. Environmental Entomology. 24: 

1529-1538.

Shigesada, N.; Kawasaki, K. 1997. Biological invasions: theory and practice. New 

York: Oxford University Press. 205 p.

Sills, E.O.; Bigsby, K. 2007. Balancing the costs and benefits of slowing the 

spread. In: Proceedings: Annual Gypsy Moth Review 2007; October 29-

November 1; Shepherdstown, WV. Charleston, WV: West Virginia Department 

of Agriculture.

Thorpe, K.; Reardon, R.; Tcheslavskaia, K.; Leonard, D.; Mastro, V. 2006. A review 

of the use of mating disruption to manage gypsy moth, Lymantria dispar

(L.). FHTET-2006-13. U.S. Department of Agriculture, Forest Service, Forest 

Health Technology Enterprise Team. 86 p.

Tobin, P.C.; Liebhold, A.M.; Roberts E.A. 2007a. Comparison of methods for 

estimating the spread of a nonindigenous species. Journal of Biogeography. 

34: 305-312.

Tobin, P.C.; Blackburn, L.M., eds. 2007. Slow the Spread: a national program to 

manage the gypsy moth. Gen. Tech. Rep. NRS-6. Newtown Square, PA: U.S. 

Department of Agriculture, Forest Service, Northern Research Station. 109 p.

Tobin, P.C.; Sharov, A.A.; Liebhold, A.M.; Leonard, D.S.; Roberts, E.A.; Learn, M.R. 

2004. Management of the gypsy moth through a decision algorithm under 

the STS project. American Entomologist. 50: 200-209.

Tobin, P.C.; Whitmire, S.L. 2005. The spread of gypsy moth and its relationship to 

defoliation. Environmental Entomology. 34: 1448-1455.

Tobin, P.C.; Whitmire, S.L.; Johnson, D.M.; Bjørnstad, O.N.; Liebhold, A.M. 2007b. 

Invasion speed is affected by geographic variation in the strength of Allee 

effects. Ecology Letters. 10: 36-43.

U.S. Department of Agriculture. 1995. Gypsy moth management in the United 

States: a cooperative approach. Final environmental impact statement. 

Volumes 1-5. Washington, DC: U.S. Department of Agriculture.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, 

sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.) 

Persons with disabilities who require alternative means for communication of program information 

(Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at 202-720-2600 

(voice and TDD). To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, 

Room 326-W, Whitten Building, 1400 Independence Avenue SW, Washington, DC 20250-9410 or 

call 202-720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

Printed on recycled paper

Tobin, Patrick C. 2008. Cost analysis and biological ramifications for 

implementing the gypsy moth Slow the Spread Program. Gen. Tech. Rep. 

NRS-37. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 21 p.

The gypsy moth Slow the Spread Program aims to reduce the rate of gypsy 

moth, Lymantria dispar (L.), spread into new areas in the United States. The 

annual budget for this program has ranged from $10-13 million. Changes in 

funding levels can have important ramifications to the implementation of this 

program, and consequently affect the rate of gypsy moth spread. This report 

presents a cost analysis for implementing the Slow the Spread Program 

across a range of funding levels, and predicts the consequent changes in 

gypsy moth spread rates. This work should be useful to program managers in 

implementing the Slow the Spread Program given yearly financial constraints, 

and more generally could serve as a template for barrier zone management 

programs against other nonindigenous species.

Key Words: Lymantria dispar, invasive species management, spread, 

biological invasions

The mention and use of product and trade names does not constitute 

endorsement by the USDA Forest Service.
Capitalizing on the strengths of existing science capacity in the Northeast and Midwest 

to attain a more integrated cohesive landscape scale research program