Timing of Attack by Lypha dubia Fall. (Diptera: Tachinidae) on the Winter Moth Operophtera brumata (L.) (Lepidoptera: Geometridae) as a Factor Affecting Parasite Success

Abstract

Operophtera brumata (L.), in several European countries and was introduced into Canada (with other species of parasites) in an attempt to control the winter moth outbreak in Nova Scotia, but failed to establish itself there (Embree 1966). However, in population models developed for the winter moth on oak at Wytham, Berkshire, Varley & Gradwell (1968) consider Lypha to be relatively unimportant; so much so that in their model they describe the effect of Lypha, together with that of some other winter moth parasites, as either a constant or a very weak inverse density-dependent mortality. Preliminary analyses of the data from Wytham showed that there were four relationships between Lypha and winter moth which were unexpected and which required further investigation. (1) Most of the Lypha larvae in winter moth larvae feeding on oak were dead, whereas most of those in winter moth on other food-plants were alive; (2) The percentage parasitism of winter moth larvae on oak was lower than that of larvae feeding on other food-plants; (3) The percentage parasitism of winter moth on the different oak trees varied inversely as the winter moth densities on those trees; and (4) The density of Lypha adults was relatively constant from year to year in spite of large fluctuations in the densities of its hosts.