Pomphorhynchus laevisin its intermediate hostEchinogammarus stammeriin the River Brenta, Italy

Infection rates of larvalPomphorhynchus laevisMu¨ller, 1776 (Acanthocephala) were studied in its intermediate hostEchinogammarus stammeriS. Karaman, 1931 (Amphipoda). Crustaceans were collected monthly, from July 1990 to July 1997, at two sites on the River Brenta (northern Italy). Of over 50,000E. stammeriexamined, more than 24% were parasitized withP. laevislarvae. The differences in the prevalence of infection between the two stations were significant. The intensity of infection varied from one to 15 acanthocephalans per host. Amphipods with multiple infections constituted 28–32% of each monthly sample. During the 7 years of investigation, the prevalence of infection typically reached its highest and lowest levels in the summer and spring months, respectively. Acanthocephalan larvae showed no preference for host sex. Infected ovigerous females ofE. stammeriwere found carrying eggs or juveniles in their brood pouches, but had fewer and smaller eggs.Pomphorhynchus laevislarvae co-occurred withAcanthocephalus clavula(Dujardin, 1845) and also with the tapewormCyathocephalus truncatus(Pallas, 1781) in the same host.