Research Article A Time Delay Predator-Prey System with Three-Stage-Structure

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Apredator-prey systemwas studied that has a discrete delay, stage-structure, andBeddington-DeAngelis functional response, where predator species has three stages, immature, mature, and old age stages. By using of Mawhin’s continuous theorem of coincidence degree theory, a sufficient condition is obtained for the existence of a positive periodic solution. 1