A simulation model of seasonal changes in the value of cattle dung as a food resource for an insect

In the Canberra region the larvae of the Australian bushfly feed in cattle dung, and the quality of this dung is an important determinant of the population dynamics of the insect. A measure of this quality is provided by the mean mass of puparia reared under standard conditions in the laboratory. This paper presents a simulation model by means of which this measure and its seasonal variation can be predicted from standard observations of rainfall, temperature and 09h00-humidity. The model is based on the growth index of Fitzpatrick and Nix, but incorporates a simple model for the phenological changes occurring in the pasture from which the dung derived. The model successfully simulates the masses of pupae reared in dung derived from a number of distinct pastures within 200 km of Canberra throughout the seasons 1970–71, 1971–72 and 1972–73.