The Effects of the Variability of Cattle Dung on the Multiplication of the Bushfly (Musca vetustissima Walk.)

Abstract

During the summer months bushflies are found over most of Australia, but in winter they disappear from the cooler (southern) third of the continent (Hughes 1970). Norris (1966) described the seasonal cycle of the bushfly in the Canberra district, in S.E. Australia. In this region there is generally a more or less unimodal population curve from October to May, but the abundance of the flies decreases markedly in late January and remains lower thereafter throughout a period of apparently still favourable temperatures. As Norris was able to show that cattle dung was the most important breeding site for the bushfly, he discussed the possibility that seasonal changes in the quantity and quality of forage in late summer would affect the dung and so have an important effect on bushfly breeding. Profound effects on the success of bushfly breeding were found in experiments using dung from different pasture and management regimes during the 1967 drought (Hughes & Walker 1970). In the field, changes in cattle dung consistency and texture are readily discernible through the spring and summer. When grazing pastures consisting predominantly of new spring growth, cattle 'scour', voiding dung that is very liquid, rich, and homogeneous. When the new growth emerges through standing winter grass the dung is thicker but is still amorphous, moist and rich. As pastures mature and vegetation becomes more fibrous, dung becomes less uniform in texture and has a stiffer consistency. On 'hayedoff' pasture, dung is composed mostly of undigested plant fibre. Being stiff and dry in consistency it forms high mounds on the ground that may persist for several years (Bornemissza 1960). The present paper reviews the composition and formation of cattle dung, indicating possible causes of the variation. It then describes the collection and analysis of dung from different localities and times of year, and assays of the effect of dung variations on bushfly population biology.