Host-parasite relationships of caryophyllaeid cestodes and aquatic oligochaetes: II. Effects of host age and mixed infections.

Experiments were conducted to assess the relationship between annelid age and susceptibility of the annelid as an intermediate host for a caryophyllaeid, as well as the effect a mixed-species infection has on rate of metacestode development and parasite mortality. Four host-parasite systems were studied: Biacetabulum biloculoides and Hunterella nodulosa in Limnodrilus hoffmeisteri and Glaridacris catostomi in Ilyodrilus templetoni and Tubifex tubifex. Annelids were divided into 3 age classes: immature, approximately 7 days old; intermediate, approximately 14 days old; and mature, approximately 30 days old. Immature oligochaetes in all groups were more susceptible to infection, their parasites exhibited a lower mortality rate than 30-day-olds, and the total number of parasites in this group was higher than for the other age classes. Metacestodes reached the infective stage earlier in immature as compared to older oligochaetes. Interspecific competition between B. biloculoides and H. nodulosa resulted in increased parasite mortality and a slower rate of parasite development for the species that became established second. A prior infection with one species of cestode also affected the susceptibility of L. hoffmeisteri to infection with another species.