BIOLOGICAL CONTROL OF 

WINTER MOTH

 IN NORTHEASTERN NORTH AMERICA

Joseph S. Elkinton1

George H. Boettner1

Hannah J. Broadley1

Richard Reardon2

Ronald D. Weeks, Jr.3

1

Dept. Environmental Conservation, Univ. Massachusetts, Amherst, MA 2

USDA Forest Service, Morgantown, WV 3

USDA APHIS PPQ, Raleigh, NC

FHAAST-2018-03

August 2018

Forest Health Assessment and 

Applied Sciences Team
This publication is available online at: 

https://www.fs.fed.us/foresthealth/

technology/pdfs/FHAAST-2018-03_

Biology_Control_Winter-Moth.pdf

The Forest Health Technology Enterprise Team (FHTET) 

was created in 1995 by the Deputy Chief for State and 

Private Forestry, USDA Forest Service, to develop and 

deliver technologies to protect and improve the health of 

American forests. 

FHTET became Forest Health Assessment and Applied 

Sciences Team (FHAAST) in 2016. This booklet was 

published by FHAAST as part of the technology transfer 

series.

http://www.fs.fed.us/foresthealth/technology/

Federal Recycling Program

Printed on Recycled Paper

Acknowledgments

Funding on this project has been provided by the USDA 

Forest Service FHAAST and USDA APHIS. We are grateful 

to the many cooperators and student workers who helped 

us collect and release Cyzenis albicans and/or samples 

of winter moths as part of this project. The layout of this 

brochure was designed by Rachel Winston, MIA Consulting.

Booklet front cover image: An outbreak of winter moth larvae, 

Operophtera brumata (Photo: George Boettner, University of 

Massachusetts, Amherst)
KEY FINDINGS

The goal of the WINTER MOTH

biocontrol program is to protect

native forests, cityscapes, 

agricultural lands, 

and sensitive ecosystems

The winter moth invaded North America prior to 

1950, causing widespread defoliation of forest 

and shade trees.

Two outbreaks in Nova Scotia and British 

Columbia were controlled with the biocontrol 

agent Cyzenis albicans, a tachinid fly.

The winter moth invaded New England in the 

1990s.

A New England winter moth biocontrol program 

was initiated in 2005 with the collection and 

release of C. albicans.

As of 2018, C. albicans has become established 

at 32 New England release sites.

Winter moth populations have sharply declined in 

eastern New England, and additional C. albicans 

releases are recommended for other winter moth 

populations elsewhere in North America.

Adult male winter moth, Operophtera brumata (Photo: Olaf Leillinger)
2

BACKGROUND 

INFORMATION

Winter moth (Operophtera brumata L., 

Geometridae: Lepidoptera), a leaf-feeding 

inchworm caterpillar native to Europe, invaded 

eastern Massachusetts in the 1990s and started 

causing widespread defoliation of forest and 

shade trees throughout the region (Fig. 1). Winter 

moth larvae feed on many kinds of deciduous 

trees, and the moth has become a major pest of 

blueberries throughout NE North America.

Fig. 1. Shade tree defoliated by winter moth larvae (Photo: Joe Elkinton, 

University of Massachusetts, Amherst)

Surveys from 2005-2007 revealed winter moths 

were established in coastal areas from Maine to 

SE Connecticut, as well as Nova Scotia (Fig. 2). 

Defoliation occurred at sites north and south of 

Boston in 2004 and spread west and south across 

Massachusetts and Rhode Island over the next 

decade (Fig. 3). Outbreak populations occurred in 

2012 for the first time in SE Connecticut and coastal 

Maine. The coastal distribution of winter moth 

mirrors that of winter temperatures exemplified by 

the USDA cold-hardiness zones (Fig 4). Colder 

winter temperatures evidently prevent winter moths 

from invading interior regions of New England and 

Canada. The same map implies, however, that 

winter moths will readily occupy interior 

regions of the USA further south.
3

Pheromone Trap 

Survey

 Winter moths 

captured

 No Winter moths 

Fig. 2. Winter moth establishment in NE North America from 2005-2007 

surveys (Elkinton et al. 2010. Ann. Ent. Soc. Amer. 103:135-145)

Fig. 3. Spread of winter moth around Boston 2004-2011 (compiled from 

annual aerial surveys, Elkinton et al. 2014 Biol. Invasions 16:2263-2272)

Fig. 4. Plant cold hardiness zone map for NE North America through 1990. 

Note: Zone 6a, which occurred in E Massachusetts and Nova 

Scotia, has now moved northward and inland encompassing 

coastal Maine and New Hampshire. (Source: USDA ARS)
4

WINTER MOTH 

BIOLOGY

Winter moths are so-named because adults 

emerge in late November and the males (Fig. 

5c) are observed flying throughout December, 

whenever temperatures are above freezing. 

The females are wingless (Fig. 5d), and after 

mating they lay eggs on the stems of trees. 

The eggs hatch in late April and larvae bore in 

the expanding buds of their host trees. Much 

of the leaf damage occurs before the leaves 

fully expand. Winter moth larvae are green and 

typical inchworms (Fig. 5a) in that they lack 

appendages in the middle of their body, resulting 

in their characteristic looping or inching gait. 

They complete development in late May and 

drop out of the tree canopies to burrow into the 

soil and leaf litter beneath the trees where they 

spin earthen cocoons in which they form pupae 

(Fig. 5b). They remain in these cocoons until 

late November, when the adults emerge and the 

cycle begins again. 

a b

c d

Fig. 5. Winter moth life stages: (a) larva, (b) pupa, (c) adult 

male, (d) adult female (Modified from photos by D. Wagner, 

reprinted from Elkinton et al. 2015, FHTET-2014-07)
5

HISTORICAL BIOLOGICAL CONTROL 

OF THE WINTER MOTH

Prior to the current invasion by winter moth to 

Massachusetts, there were two previous invasions 

to Canada—Nova Scotia prior to 1950 and British 

Columbia in the 1970s. Both prior invasions had been 

suppressed by the introduction of parasitic insects 

attacking winter moth in Europe, in particular the 

tachinid fly Cyzenis albicans (Fig. 6a). The immature 

fly develops and forms a pupa inside the infected winter 

moth pupa (Fig. 6b), killing the moth in the process.

a b

Fig. 6. Cyzenis albicans (a) adult, (b) puparium inside winter moth pupa 

(Photos: Nicholas Condor)

Cyzenis albicans was first released in Nova Scotia in 

1954. Initial recoveries of the flies occurred in 1957, 

and parasitization of winter moth larvae increased 

from 10% in 1959 to 60% in 1962, whereupon winter 

moth populations at the release site collapsed. 

Winter moth densities have remained at low levels in 

Nova Scotia (Fig. 7) and British Columbia ever since, 

similar to levels in most of Europe.

Fig. 7. Defoliation by winter moth and percentage of parasitism 

by Cyzenis albicans in Nova Scotia in the 1950s (adapted from 

Embree 1965 and Elkinton et al. 2015, FHTET-2014-07)
6

BIOLOGICAL CONTROL OF THE

WINTER MOTH IN NEW ENGLAND

Researchers at the University of Massachusetts, 

Amherst initiated a winter moth biocontrol 

program in New England in 2005. Over the 

next decade, they obtained the tachinid fly, C. 

albicans, by collecting winter moth caterpillars 

infested with immature flies from Vancouver 

Island, where both the fly and its winter moth 

hosts were introduced in the 1970s. 

The tachinid flies were reared over the winter 

and released the following spring at sites across 

New England (Fig. 8). 

Monitoring efforts in subsequent years indicated 

that this fly successfully established in New 

England. 

As of 2018, the fly had been released at 44 sites 

and had established at 32 (Fig. 8). 

Furthermore, at six widely spaced sites, longterm studies showed that as of 2017, parasitism 

of winter moth by C. albicans had increased 

coincident with a sharp decline of winter moth 

densities (Fig. 9). 

Winter moth defoliation has now largely 

disappeared in New England. It thus appears 

that C. albicans has converted winter moth to 

a non-pest status that seems likely to persist 

indefinitely, much as it did in Nova Scotia in 

the 1950s.
7

Fig. 8. Cyzenis albicans release and recovery sites in New England 

2005-2018 (Drawn by G. Luzader and A. Liebhold)

Fig. 9. Density of winter moth pupae (red) and percent parasitism by Cyzenis 

albicans (blue) at six widely spaced sites in Massachusetts indicated by the 

symbols with capital letters in Fig. 8. The blue symbols begin the year of first 

release. Green stars indicate years C. albicans was first recovered at each 

site (Elkinton et al. unpublished data)
8

WHAT YOU CAN DO

Look for evidence of the winter moth

Although winter moth attacks a wide variety 

of plants, it is especially problematic on oak, 

maple, birch, apple, and blueberry

Look for heavy defoliation (Fig. 10)

accompanied by high densities of winter 

moth larvae (green inchworms, see brochure 

cover and Fig. 5) in May

Look for large numbers of small brown moths 

(wingspan ~1 inch) flying in late November 

or December. Adults of most other common 

moth species are not active at that time

Fig. 10. Tree defoliated by an outbreak of winter moth larvae 

(Photo: Hannah Broadley, University of Massachusetts, Amherst)

If you live in coastal and eastern New England 

and have high densities of winter moth, do 

nothing. Cyzenis albicans will catch up and 

reduce winter moth populations

If you live in western New England or further south 

and west and encounter high populations of what 

appears to be winter moth, proper identification 

is warranted. Contact Joseph Elkinton at the 

University of Massachusetts, Amherst for more 

information (elkinton@umass.edu). DNA-based 

identification is readily available. USDA permits 

are required to make new releases of 

Cyzenis albicans.
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Booklet back cover images: Winter moth larvae (top) and defoliation 

damage (middle and bottom) (Photos: Hannah Broadley, University 

of Massachusetts, Amherst)