Effects of coinfection with Pomphorhynchus bulbocolli on development of Leptorhynchoides thecatus (Acanthocephala) in amphipods (Hyalella azteca)

The effect of the presence of Pomphorhynchus bulbocolli on the development of Leptorhynchoides thecatus (Acanthocephala) in amphipod intermediate host s (Hyalella azteca) was examined. Two groups of amphipods were exposed eith er to eggs of both species (experimental) or only to L. thecatus eggs (cont rol). Amphipods of both groups were dissected 39 days postexposure. The per centage of L. thecatus at the cystacanth stage and mean abundance of cystac anths and precystacanths per amphipod were determined. Contingency table an alysis and Fisher's exact tests demonstrated that a significantly smaller p roportion of L. thecatus reached the cystacanth stage in coinfected amphipo ds of the experimental group than either worms in the control group or worm s in L. thecatus-only infections of the experimental group. Interspecific i nteraction between acanthocephalans in intermediate hosts has not been repo rted previously. Coinfection reduces the number of L. thecatus in amphipods available for transmission to definitive hosts. Habitat separation by eggs of L. thecatus and P. bulbocolli might reduce this effect if amphipods are less likely to become coinfected when eggs are in different microhabitats than when they are not.