Adult winter moths usually begin to emerge around Thanksgiv- ing, or earlier, as evidenced last fall on November 16, 2017, as reported by Deborah Swanson (UMass Extension Horticulturist for Plymouth County, Retired) in Hanson, MA. Adult emergence continues through December and even into January, whenever air temperatures are mild (above freezing) and the ground remains unfrozen. Small, light brown male moths can be seen flying around, often attracted to porch lights or other outdoor light sources. Females are wingless and cannot fly; they crawl up tree trunks and release a pheromone to attract males for mating. Since 2005, Dr. Elkinton and his laboratory, with the help of dedicated volunteers, have managed the large task of collecting, releasing, and monitoring the efficacy of Cyzenis albicans, a tachinid fly parasitoid of the winter moth as a biological control agent attacking winter moth (C. albicans can only successfully develop in winter moth). This fly was originally from Europe and had previously been established, in other North American locations such as Nova Scotia in the 1950’s, with much success in reducing outbreak populations of winter moth to a non-pest status. The female fly (Cyzenis albicans) lays its eggs (up to 1,000 of them) on host plant foliage of the winter moth, and while feeding, winter moth caterpillars will eat the eggs of the flies. The egg will hatch and a tiny fly maggot will lie in wait, inside the immature winter moth, until the caterpillar is done feeding and drops to the ground to pupate. The immature fly maggot will then complete its development inside of the winter moth pupa, where it will remain until the following spring. In the spring, at approximately the same time winter moth eggs hatch, the flies (Cyzenis albicans) emerge from the deceased caterpillar pupae in the soil, mate, and lay more eggs for more caterpillars to ingest. There is one generation of flies per year. To collect the fly, Elkinton’s lab manager George Boettner trav- eled each April-May for seven years to Vancouver Island in British Columbia where both winter moth and the fly were established in the 1970’s. At that location, he managed a crew of helpers who collected many thousand winter moth caterpillars over about a one-month period. About half of the winter moth caterpillars they collected had the fly larva inside them. The flies were then reared to the pupal stage in the laboratory in Massa- chusetts and the adult flies released at various locations the fol- lowing spring. To date, the Elkinton lab has released Cyzenis albicans at 43 sites in MA, CT, RI, and ME. The fly has been established at 32 of those locations and the Elkinton lab has evidence of its ability to spread throughout the local winter moth population at those sites from the initial point of release. They now have data for sites located in Falmouth, Hanson, Hingham, Wellesley, Wen- ham, and Yarmouth, MA indicating that parasitism of winter moth pupae by C. albicans ranges from 15-48%. Typically, this might not be high enough of a percentage to reduce a pest popu- lation, but in the case of winter moth – that is what the data shows at these locations. As parasitism rates for the tachinid fly increase, the density of healthy winter moth pupae decreases. So how are these tachinid flies able to have such an impact on the winter moth population at this time? Data collected by the Elkinton lab shows that native predators in Massachusetts prey heavily on winter moth pupae in the soil where they reside between May and November. At their research sites, Hannah Broadly, one of Dr. Elkinton’s PhD students, has trapped and identified 29 species of predatory ground beetles (Carabidae) feeding on winter moth pupae. She has also identified what may be a previously undescribed (unknown to science) parasitoid wasp in the genus Pimpla (Family: Ichneumonidae).