Biological Control of Winter Moth in New England

Joe Elkinton – Dept. of Plant, Soil and Insect Sciences, University of Massachusetts, Amherst

The winter moth, Operophtera brumata, originally from Europe, invaded eastern Massachusetts more than a decade ago and has caused widespread defoliation of many deciduous tree species ever since. The infestation has spread to Rhode Island and is expanding westward in Massachusetts.  Invasions of winter moth have occurred at other sites in North America, namely Nova Scotia in the 1950s and in the Pacific Northwest in the 1970s. In each case, a decade-long outbreak was successfully and permanently controlled by the introduction of a parasitic fly from Europe named Cyzenis albicans. This fly is one of several natural enemies that attack European winter moth and keep it from being a pest in its native region. In Nova Scotia, C. albicans was first released in 1954. High levels of parasitism did not occur until 1961, but after that winter moth retreated to low density, where it has remained ever since. A great advantage of C. albicans is that it is highly specialized on winter moth, so it will not spread to other species and its numbers will decline once it controls winter moth. The fly focuses its attention on winter moth and is not attracted to humans or our homes and buildings, so the only impact that people will notice is the decline in damage caused by winter moth.

Because C. albicans was so successful in controlling winter moth in Nova Scotia and the Pacific Northwest, it was natural for us to introduce it here in New England. A research team led by Joe Elkinton at the University of Massachusetts in Amherst has been doing that since 2005 using flies that he and his colleagues collected in British Columbia. We achieved an important milestone in this effort in 2010. For the first time in six years, we have concrete evidence that we have now successfully established C. albicans at five of six release sites. We have recovered winter moth larvae parasitized by these flies at sites in the Massachusetts towns of Seekonk, Hingham, Falmouth, Wenham and Wellesley.  These were sites where we had not released C. albicans for the previous one to three years. Thus, the flies we recovered there must have successfully over-wintered and reproduced.. We conducted DNA tests to prove that the flies we recovered were identical to the ones we released. Our experience now matches closely the Nova Scotia project, wherein the yearly releases began in 1954, but no recoveries at all were made until 1959 (Fig 2).  Previous experience in Nova Scotia or British Columbia suggests that the levels of parasitism should now build rapidly over the next few years.

Until 2011 we released all of our flies at one or two sites each year and have done repeated releases at the same sites in subsequent years. We did this we were trying to assure establishment of the fly.  Now that we know that single releases with a few hundred flies can still result in establishment here in New England, we can spread the flies we have to more new sites and not release repeatedly at the same sites.  Accordingly, we have released about 700 flies at each of nine new sites in 2011, including one site in Rhode Island. In addition, we have collected more C. albicans for release next year by collecting parasitized winter moth larvae in British Columbia last May. From this effort we have 61,000 winter moth pupae, which now reside in the USDA quarantine lab at Otis Airbase. Previous experience tells us that about 50% of these pupae will contain immature C. albicans.  Assuming that we can successfully rear most of these to the adult stage next spring, we should have more flies to release than ever before in May 2012.

Defoliation map is courtesy of the Mass. Dept. of Conservation and Recreation.

Fig. 1. Cyzenis albicans release sites in Massachusetts  2005-2011. In 2011 we released at nine new sites more than doubling the number of release site from prior years.