Winter Moth and Gypsy Moth Update
Winter moth and gypsy moth are two insects that have defoliated areas of Massachusetts in the recent past. These defoliation events have left many wondering what to expect in 2019.
Winter moth was identified causing defoliation in Massachusetts in the 1990s and previously had caused defoliation outbreaks in Nova Scotia and British Columbia. Winter moth caterpillars defoliate trees by feeding on emerging buds of deciduous forest and shade trees. Shortly after winter moth was identified, researchers at the University of Massachusetts Amherst, led by Dr. Joseph Elkinton, began a biological control effort using a tachinid fly, Cyzenis albicans. C. albicans is a parasitic fly that develops as a pupa inside the infected winter moth pupa, killing the winter moth in the process. C. albicans was a primary reason for winter moth populations being reduced to below pest levels in both Nova Scotia and British Columbia.
The work of Dr. Elkinton’s team has included the collecting, rearing, and releasing of C. albicans since 2005. In that time, the fly has been released at 44 sites and found to be established at 32 of them. Research at several of the release sites has shown parasitism of winter moth by C. albicans and a corresponding decline of winter moth densities. Winter moth populations in eastern New England are now at an all-time low since 2005 and defoliation from winter moth has largely disappeared. The decline has for the most part has reduced winter moth to a non-pest status similar to what occurred in Nova Scotia as a result of C. albicans and the hard work of Dr. Elkinton’s team. To read more about this, go to https://www.fs.fed.us/foresthealth/technology/pdfs/FHAAST-2018-03_Biology_Control_Winter-Moth.pdf
Gypsy moth was introduced into the US in the late 1860s accidently here in Massachusetts. Gypsy moth had been responsible for periods of wide spread defoliation in Massachusetts, with the largest defoliation occurring in 1981. In 1989, the entomopathogenic fungus Entomophaga maimaiga was found infecting gypsy moth caterpillars. Since that time, the population of gypsy moth has not caused widespread defoliation in Massachusetts until recently. Starting around 2015, increased populations of gypsy moth were being observed as a result of a lack of adequate precipitation during crucial parts of the gypsy moth caterpillar’s development in the spring, reducing infections by E. maimaiga and leading to population increases in gypsy moth. Over the next 2 years, gypsy moth caused widespread defoliation, peaking in 2017 and causing almost 1 million acres of defoliation in Massachusetts.
In 2017, early summer rains lead to widespread mortality of the gypsy moths by E. maimaiga. Defoliation was greatly reduced in 2018, resulting in approximately 150,000 acres of defoliation. The MA Department of Conservation and Recreation Forest Health Program conducted their annual egg mass survey, which helps predict the potential for defoliation (Figure 1).
Fig 1. Mass DCR Gypsy Moth Egg Mass Survey Results 2018
There seems to still be a concentration of high egg mass numbers in central Massachusetts for 2019. Outside of that area, egg mass numbers appear to be spottier. Look closely at your trees for gypsy moth egg masses to determine whether management may be necessary this year. For more info on managing gypsy moth, go to https://ag.umass.edu/sites/ag.umass.edu/files/pdf%2Cdoc%2Cppt/final_gypsy_moth_fact_sheet_1_column.pdf For info on current conditions, go to https://www.mass.gov/guides/gypsy-moth-in-massachusetts.
The years of defoliation from winter moth, gypsy moth, cynipid gall wasp and the severe drought of 2016 have left a lot our trees, especially oaks, in a state of decline or poor health. These stresses have weakened many of our trees, making them susceptible to further attacks by boring insects like two lined chestnut borer and decay fungi like Armillaria. So, even though winter moth and gypsy moth may not be as a significant threat as in the recent past, don’t forget to keep a close eye on the health of your trees and consider hiring a tree care professional to evaluate tree health and make management suggestions.
Russ Norton, Agriculture & Horticulture Extension Educator, Cape Cod Cooperative Extension