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Gypsy moth is a destructive, exotic forest pest that was accidentally introduced into the United States in 1869. It is currently established throughout the northeast and parts of the upper mid-west.

  • It feeds on over 300 species of trees but oaks are most preferred.
  • 75 million acres have been defoliated by gypsy moth since 1970.
  • Gypsy moth defoliation causes extensive tree mortality, reduces property values, adversely affects commerce and causes allergic reactions in sensitive individuals that come in contact with the caterpillars.
  • Most (almost 70%) of the susceptible hardwood forests in the United States have not been infested by gypsy moth and are still at risk.

Since Congress funded the Slow the Spread Program (STS) in the year 2000, eleven states located along the leading edge of gypsy moth populations, in cooperation with the USDA Forest Service, have implemented a region-wide strategy to minimize the rate at which gypsy moth spreads into uninfested areas.  As a direct result of this program, spread has been dramatically reduced by more than 70% from the historical level of 13 miles per year to 3 miles per year.  In its first 6 years, this program prevented the impacts that would have occurred on more than 40 million newly infested acres.

  • STS reduces spread of this destructive pest to 3 miles per year, which will prevent infestation of more than 150 million acres over the next 20 years.
  • STS protects the extensive urban and wildland hardwood forests in the south and upper mid-west.
  • STS protects the environment through the use of gypsy moth specific treatment tactics.
  • STS unifies the partners and promotes a well coordinated, region-wide action based on biological need.
  • STS yields a benefit to cost ratio of more than 4 to 1 by delaying the onset of impacts that occur as gypsy moth invades new areas.


While traditional approaches to gypsy moth management address potentially defoliating populations occuring in generally infested areas, the STS project focuses on populations in the area between that of general infestation and generally uninfested. In this transition zone, populations are low and somewhat discontinuous. Male moths are the primary population indicators, and other life stages are rarely found. The project attempts to meet its goals by conducting intensive monitoring with pheromone-baited traps in order to detect isolated or low-level populations in the transition zone. Although all available tactics to control gypsy moth populations will be considered, emphasis is placed upon the most environmentally benign tactic which meets management objectives.


The STS Project is composed of two types of management areas: the Action Area, where STS management strategies are applied, and the Evaluation Area, where normal state and federal management strategies are maintained. Data from the Evaluation Area, along with data from surrounding state gypsy moth surveys, will be used to assess the efficacy of STS management strategies in the Action Area. Intensive monitoring within the Action Area is the foundation of the project and provides the trap catch data used in a decision-making algorithm to determine the appropriate management activities.

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