Some Ecological Relationships of Natural Populations of Calliphorine Blowflies

Abstract

Relation of blowfly populations to season and to vegetational environment was studied a number of years by serial trappings on periphery of an aerodrome in a mixed-farming area near Carlisle. Throughout blowfly season the population consisted mainly of Calliphora erythrocephala, and this sp. was 1st to appear and last to disappear. Lucilia caesar group formed a 2d major component in the summer months, representing up to 40% of the total. In this group, L. illustris was slightly more frequent than L. caesar and L. ampullacea relatively scarce. Lucilia sericata and L. silvarum, Phormia terraenovae and Cynomyia mortuorum were all present in low numbers only; Calliphora vomitoria occasionally represented up to 10% in late season. Other spp. of calliphorine blowflies were caught rarely. Differences between spp. occurred in the sex-ratio of trapped samples, and these varied between seasons and for different types of habitat. A species-pattern similar to the above was obtained on reclaimed bogland and on upland sheep-grazing. General proportions of major spp.-groups in the population were confirmed by tent-trapping of the ground without attractant bait. Calliphora vomitoria and Lucilia ampullacea apparently need dense cover such as wood. Calliphora erythrocephala was more numerous in the open near hedgerows than in wood, Lucilia caesar preferred tall-field-layer with some interrupted canopy, and L. illustris rather more open conditions. There is possibly a shift of some spp. of the caesar group population into more open conditions in the late part of the season. Relatively more males of Calliphora and Lucilia were caught by bait-traps in canopy habitats than elsewhere; this was not confirmed by the tent-trap catches. Calliphora erythrocephala was estimated by the release - recapture method at 50 to 200 flies per acre in August, 400 to 1000 in September, and 700 to 1000 in October. The caesar group was estimated as 40 to 70 per acre in August and September, and under 1 per acre (Lucilia caesar) in October. Lucilia sericata and Cynomyia mortuorum were estimated to be in very low numbers. Bait-trap estimates of the population of ecologically uniform subsections of the area showed significant differences in population level and also differences in species-pattern. The concept of arenas of activity as applied to blowflies is outlined in general terms. Some limitations to the use of the release-recapture method of estimating numbers are discussed in relation to the results.