Numerical Changes and Resource Utilization in Orchard Populations of Drosophila.

Abstract

Drosophila were collected monthly at a south-east Australian orchard site over 30 months. D, melanogaster was predominant in spring-summer, D. simulans in autumn, and D. immigrans in winter. These seasonal changes are consistent with trends described in an earlier study by McKenzie and Parsons (1974). Numbers of the endemic species D. lativittata tended to follow those of D. melanogaster. Comparisons of numbers of each species with environmental variables indicate that D. melanogaster is positively correlated, and D. immigrans negatively correlated, with temperature parameters. D. simulans and D. lativittata numbers were independent of all climatic variables tested. These associations are consistent with collections by McKenzie and Parsons (1974) from an orchard site, but not from their suburban sites. The associations of numbers of adults of each species with climatic variables are only in partial agreement with results from laboratory experiments on stress in adults. Sampling within the orchard indicates that D. melanogaster and D. simulans are differentially associated with fruit resources at both adult and larval stages, with D. melanogaster predominating on peach resources.