Abstract
The history of the winter moth, Operophtera brumata (Linnaeus), a geometrid introduced into Nova Scotia, is reviewed and an assessment is made of two introduced parasites: a tachinid, Cyzenis albicans (Fallen), and an ichneumonid, Agrypon flaveolatum (Gravenhorst). Functional response curves of both species are discussed, particularly the atypical S-shaped curve of C. albicans, which demonstrates regulatory properties. Biological control efforts to date have been successful but a virus that appeared in winter moth populations may change initial relationships between the introduced parasites and the host.