Population Dynamics of Hymenolepis diminuta in the Intermediate Host

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Abstract
Results are presented of experiments designed to investigate possible regulatory processes in the dynamics of the [rat] cestode H. diminuta in the intermediate host (Tribolium confusum). No density-dependent constraints on larval parasite establishment within individual hosts were found up to parasite burdens of 60 per beetle. An inverse relationship between cysticercoid length and cysticercoid burden per host indicated that intraspecific competition is operative once the parasites become established within the hemocoel. No density-dependent decrease in the infectivity of cysticercoids to the final host was demonstrated up to parasite burdens of 60 per beetle. A decrease in infectivity occurred with increasing cysticercoid age, beginning at approximately 4 wk post-infection. The mean parasite burden of populations of T. confusum exposed to known densities of H. diminuta eggs rose to a plateau with increasing egg density, and may have resulted from limitations imposed on parasite acquisition by the feeding behavior of the host. A functional response was demonstrated between prey density and the rate of predation of T. confusum by laboratory rats. The results of long-term experiments under specified laboratory conditions revealed a 50% depression of T. confusum equilibrium population level as a result of parasitism by H. diminuta. The experimental results are discussed in relation to the effectiveness of the various potential regulatory factors on parasite population growth under natural conditions.