Life Cycle of the Mayfly Nymph, 'Hexagenia,' in the St. Marys River

摘要

Length-frequency distribution curves of Hexagenia nymphs collected in May, August, and October 1974, and May 1975 in the St. Marys River revealed a bimodal distribution for each sampling period. These curves indicate that the population of Hexagenia nymphs in the St. Marys River is composed of two year classes or cohorts. One cohort emerges per season, 2 years after egg deposition. This 2-year life cycle contributes to the stability of the food chain by providing a relatively constant supply of nymphs to predators.