In the establishment of insect parasites, the production of large numbers for release in heavily infested areas is often desirable. This was especially true in the case of parasites of the European spruce sawfly, Gilpinia hercyniae Htg. The rapid increase in numbers nad extent of the sawfly infestation in Canada with the resulting losses in timber as reported by Balch (1940) and Baird (1940) created a situation of grave concern, and the need for rapid colonization of insect parasites as part of the general control programme was considered urgent. Of the parasites chosen for introduction, the tachinid Sturmia sp. was considered very promising. Following initial establishment of this species, it was decided that an attempt should be made to propagate it in numbers sufficient for widespread distribution either by improving the methods in use at that time or by devising radically different methods.