A comparative study of resource utilization in natural populations of Drosophila melanogaster and D. simulans

Data were collected over four vintage seasons at the "Chateau Tahbilk" winery. The distribution of adults, larvae and pupae of D. melanogaster and D. simulans was recorded over a pile of grape residues during two different stages of its decomposition. Active fermentation characterized the first of these stages, but was much less apparent in the later stage. The distribution of adults was similar for both stages. However, while larvae and pupae of both species were observed in the post fermentation residues essentially only D. melanogaster larvae and pupae were present during the fermentation stage. During this stage larvae were aggregated beneath the surface to a depth of 10 cm. Here the average temperature was about 29°C and ethanol and acetic acid concentrations were around 7% (v/v) and 3% (v/v), respectively.Laboratory results allow a description of the physiological and behavioural responses of both species to ethanol or acetic acid concentration and to temperature differences. These results appear sufficient to explain the distribution of the species between and within the residue stages. However, before general statements of resource utilization or species interaction can be made, the need to study different stages of the life cycle is highlighted.