The life cycle and seasonal variation of Davainea tetraoensis Fuhrmann 1919, a cestode parasite of ruffed grouse, Bonasa umbellus (L.)

Abstract

Ruffed grouse (Bonasa umbellus) were collected from August 26, 1965, to August 25, 1966, and examined for cestodes. Two morphological variations of Davainea tetraoensis were found, fully developed mature worms being recovered during the summer months and poorly developed winter forms with no mature prolottides being recovered during the winter months. Various causes are considered and investigated experimentally. Changes in diet and changes in photoperiodicity do not seem to effect any change from one form to the other; changes in temperature, however, seem to be closely related to the transition from summer forms to winter forms, this transition occurring at around 0C. The change back to mature forms may be linked to gonad development in the host or to those environmental factors which influence gonad development. Cysticercoids from experimentally infected molluscs are described and compared. The rate of development of cysticercoids in Zonitoides arboreus under different conditions is investigated showing that full development, from oncospheres, can occur within 12 days in small individuals (2 mm) but takes at least 19 days in larger individuals (4.5 mm). Examination of grouse and chickens after experimental infection with up to 450 cysticercoids showed no apparent ill effects, or damage of any kind, to the hosts.