Sucrose-stimulated searching behaviour of Drosophila melanogaster in a uniform habitat: modulation by period of deprivation

Abstract The local searching behaviour of sucrose-fed, apterous Drosophila melanogaster was analysed to quantify the effects of starvation on search parameters and to determine if a genetic dissection of local searching behaviour was feasible. Three distinct ‘searching states’ were observed: pre-feeding ranging prior to feeding, local searching immediately following feeding, and post-feeding ranging after local searching was terminated. Differences between the first and third states indicate that the searching behaviour of D. melanogaster is not a simple alternation between ranging and local searching. Unfed D. melanogaster females walk relatively straight in the horizontal plane, a phase of searching referred to as pre-feeding ranging. Locomotory rate declines as the period of starvation increases from 0 to 48 h. Time actually spent moving increases to a maximum at 3–12 h of starvation and then declines. Satiated flies and flies starved for 48 h move very little. After a fly feeds on a drop of sucrose, its local searching is characterized by a decrease in locomotory rate and an increase in turning rate. These values then decay to post-feeding asymptotes. Flies starved longer than 24 h exhibit a somewhat different pattern of changes in the motor values. The duration of local searching increases with the period of starvation. ‘Thoroughness’ values, a combination of path length and minimum circumscriptive circle, demonstrated that there were periodic bouts of searching, and a decline over time in the amplitude of area-restricted searching. The relative time spent ranging and searching and the rate of movement during these activities are discussed in terms of differing energy reserves resulting from a balance between the period of starvation and food intake.