LARVAL FORAGING BEHAVIOR AND COMPETITION IN DROSOPHILA-MELANOGASTER

Populations of Drosophila melanogaster derived by bidirectional select ion for high (HA) and low (LA) aggregated oviposition behaviour differ significantly in the duration of the larval period and adult size bec ause of differences in the developmental profiles for feeding rate ove r successive phases of larval growth. Feeding rates of HA larvae are s ignificantly lower than those of LA larvae during the flexible period of growth which precedes attainment of critical mass for pupation. Con sequently the HA larvae have a slower mean rate of development. In the fixed postcritical period of development the feeding rates of HA larv ae are significantly higher than those of LA larvae. This causes a gre ater postcritical growth increment and larger adult flies. HA and LA l arvae respond adaptively by changing the expression of components of t heir foraging behaviour depending on whether they are in or out of foo d. LA larvae exhibit a more flexible pattern of response and are also more successful competitors when food resources are limiting.