Yellowstone National Park Report
Aspects of the life cycle of D. cordiceps have been known for more than a century, viz., the occurrence of plerocercoids in the secondary intermediate host(s), cutthroat (and other) trout, in Yellowstone National Park (Leidy, 1872); and the development of the adult parasite in various homoithermic definitive hosts (pelican, gull, bear, others) on ingestion of the larval plerocercoids with the flesh of the infected intermediate host (Scott and Honess, 1934). Attempts by various workers to complete the life cycle by incubation and matching of eggs of the tapeworm and infection of the primary intermediate host (presumably some copepod) have been unsuccessful (Crosby, 1970; Post, 1971).
Kingston, N. and Diem, Kenneth L.
"The Life Cycle of Diphyllobothrium Cordiceps (Cestoda: Pseudophyllidea) in Yellowstone Lake,"
University of Wyoming National Park Service Research Center Annual Report: Vol. 2
, Article 22.
Available at: http://repository.uwyo.edu/uwnpsrc_reports/vol2/iss1/22