Ecological investigations of the pitcher plant sarcophagid fly (Blaesoxipha fletcheri) indicate that larvae of this species are highly aggressive. The ecological basis of the larval behavior and spacing system is examined in terms of resource utilization. The unusual reproductive biology of the fly is analyzed within the context of r and K selection. The number of pitcher plant (Sarracenia purpurea) leaves ultimately limits the density of B. fletcheri larvae. Intraspecific competition for the leaf microhabitat and for food produces high density-dependent mortality and a spacing system of one B. fletcheri larva per pitcher leaf. The reproductive strategy of B. fletcheri reflects this density dependence in that comparatively few, but very large, competitive larvae are produced. It is suggested that B. fletcheri is a K strategist relative to many other sarcophagid species. The reproductive resource allocation method is potentially not sufficient for recognition of K strategy in B. fletcheri or other species.
A study of the phytotelmata of the pitcher plant, Sarracenia purpurea, was conducted from April through October 1973. Data on larval densities of Blaesoxipha fletcheri are based on 200 Sarracmia purpurea pitchers collected in 10 sets of 20 at 6-day intervals during June and July 1973. The localities from which this material was sampled were two Sphagnum bogs located near the Queen's University Biological Station, Chaffey's Locks, Ontario. A set of simple behavior experiments is described in a subsequent section.