Cyzenis albicans is a species of fly in the family Tachinidae. A parasitoid, it lays its eggs on leaves of oak, maple, birch and other trees, so that when the leaves are consumed by the larvae of the host winter moth, the eggs hatch inside the larvae. The fly is native to Europe and Asia but has been introduced into North America as a biological control agent of the invasive winter moth. Ecology Cyzenis albicans is a parasitoid, the female laying its eggs on the surface of leaves which are then eaten by the larvae of suitable host moth species. This fly is synovigenic, continuing to produce and mature eggs throughout its adult life and needing to feed in order to do so. The fly larvae feed internally on the moth larvae, pupating within the moth pupae when their hosts have fallen to the ground, and emerging as adults the following spring. Hosts In Europe and Asia, where this fly is native, the larvae of several geometrid moths are parasitised. These include the winter moth (Operophtera brumata), the northern winter moth (Operophtera fagata), the oak nycteoline (Nycteola revayana), the elm autumn moth (Ypsolopha vittella) and the pimpinel pug (Eupithecia pimpinellata). In North American, where it has been introduced, it is only known to use winter moth (Operophtera brumata) as a host. Use in biological control The winter moth first appeared in Nova Scotia, Canada, in the 1920s. By 1949 it had spread, causing defoliation of trees on a wide scale, and had been identified as a pest species. In 1954 and 1955, several insect species were introduced from Europe in an attempt to control it. The most successful of these were the parasitic wasp Agrypon flaveolatum and the parasitoid fly C. albicans, both of which became established in Canada. As the numbers of parasites built up, so the populations of the winter moth declined. Winter moths were first noted in the United States in the late 1990s in the state of Massachusetts. During the next decade they spread from Boston, south to Martha's Vineyard and Cape Cod, into Rhode Island, and Connecticut. There also have been outbreaks of winter moth in coastal New Hampshire and Maine. Winter moth defoliates maples, oaks, fruit trees, and other deciduous trees. Attempts at biological control followed with the release of C. albicans since 2005. The wasp was considered unsuitable because it is unknown if