This paper studies a class of periodic n species cooperative Lotka-Volterra systems with continuous time delays and feedback controls. Based on the continuation theorem of the coincidence degree theory developed by Gaines and Mawhin, some new sufficient conditions on the existence of positive periodic solutions are established.
"Positive Periodic Solutions of Cooperative Systems with Delays and Feedback Controls." Int. J. Differ. Equ. 2013 (SI2) 1 - 9, 2013. https://doi.org/10.1155/2013/502963