A Long-Term Study on the Population Biology of Crepidostomum cooperi (Trematoda: Allocreadidae) in the Burrowing Mayfly, Hexagenia limbata (Ephemeroptera)

Abstract

A 16-year study (1969-1984) considered aspects of the population biology of Crepidostomum cooperi (Trematoda: Allocreadidae) in the burrowing mayfly Hexagenia limbata (Ephemeroptera). The study site was Gull Lake, a mesoeutrophic system in southwestern lower Michigan. Prevalence of C. cooperi metacercariae was, except for one period of 2 consecutive years, significantly higher in female subimagoes. Prevalence in male mayflies varied between 75 7O and 907O in all but 4 years; among females it was >90% in all but 3 years. Densities of metacercariae were consistently higher in female mayflies in all 16 years. There was a significant increase in density of the parasite from 1969 through 1976, followed by a significant decrease over the next 6 years; densities have risen substantially in the last 2 years. The prevalence and abundance of C. cooperi in mayfly nymphs was higher in shallow parts of the littoral zone (3 m) than at 5 or 7 m. The pattern of distribution of the parasite in mayfly nymphs and subimagoes is believed to be related to the eutrophication which has occurred in the lake during the past 15-20 years.