The gypsy moth has been a costly and persistent problem in Massachusetts since its introduction in 1869. This invasive pest causes tree defoliation through its spring feeding in the caterpillar life stage.
Guide Gypsy Moth in Massachusetts
History of Gypsy Moth in MA
The gypsy moth, Lymantria dispar, has been a costly and persistent problem in Massachusetts since its introduction in 1869. This invasive pest causes tree defoliation through its spring feeding in the caterpillar life stage. The first major defoliation in event in Massachusetts occurred in 1889. It is at this point Massachusetts state agencies became involved and began efforts to control gypsy moths. Gypsy moth management began as a laborious process, including egg mass removal and treatments applied by hand, but as technology advanced, efforts progressed to the use of spray trucks and eventually aerial pesticide applications (including the use of DDT). Despite continued efforts of control, they gypsy moth spread to every city and town in Massachusetts by 1922 and has remained a major threat to forest health in the state.
Gypsy Moth Management Plan
Massachusetts’ management approach to gypsy moth has greatly shifted from the early days of infestation; Massachusetts state agencies currently rely on nature to manage gypsy moth populations. Weather, natural and introduced enemies, and the resilience of our forests to withstand gypsy moth defoliation are all parts of this natural system. Gypsy moth populations in Massachusetts have generally experienced cyclical patterns; large population booms are interspersed by years of low population density.
Drought conditions in recent years had limited the effectiveness of a soil borne fungus, Entomophaga maimaiga, which has helped keep gypsy moth populations in check since the last large outbreaks of the 1980’s. Starting in 2015 and 2016, Massachusetts experienced an increase in the gypsy moth populations, culminating in a severe outbreak in 2017. This 2017 population boom caused over 923,000 acres of damage statewide in Massachusetts. Fortunately, ideal conditions allowed for high mortality rates of the caterpillars from the E. maimaiga fungal infections and NPV virus. Caterpillar mortality rates exceeded 90% in some locations. Though the population has peaked and we have seen a severe decline in viable egg masses and do not expect another year of widespread defoliation, gypsy moths will still be present in 2018. We are expecting there to be regionalized pockets of defoliation in Essex, Hampden, Hampshire, Norfolk, and Worcester Counties.
For More Information
To learn more about gypsy moth outbreaks in MA, contact the DCR's Forest Health Program.