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Article written by L.L. Thomforde and Calvin R. Fremling regarding instructions for mayfly rearing in the controlled setting of a laboratory, including methodology and results. Abstract: "Mass emergences of Hexagenia bilineata (Say) from the Upper Mississippi River tend to occur at intervals of about 6-11 days. It has seemed likely that the waves of emergence are indicators that sub-populations or "broods" have developed sympatrically and that the short-lived adults of one emergence peak are sexually isolated by time from adults of preceding and succeeding peaks. However, preliminary experiments with laboratory populations showed that the progeny resulting from eggs laid during the time of one mass emergence will emerge at intervals and en masse over an 11-month period. It seems probable that the broods in the river may include adults from last-instar nymphs of varying ages which have emerged at the same time. Complete sexual isolation, discrete gene pools, and resulting sympatric speciation of the broods therefore seem unlikely." Fremling and Thomforde are credited as, respectively: "Professor of Biology, Winona State College, Winona, Minn." and "Biology Instructor, John F. Kennedy High School, Bloomington, Minn." Article reprinted from the Annals of the Entomological Society of America, volume 61, number 5, September 1968. 5 pages. Part of the Cal R. Fremling Collection.

Publication Date


Item Type





Winona, Minnesota


Biologists; Mayflies; Laboratory


Special Collections-Library



Rights Management

Requests to reproduce this image must be granted by the Winona County Historical Society.

Contributing Institution

Winona County History Center

Master File Format


Fiscal Sponsor

This project has been financed in part with funds provided by the State of Minnesota from the Arts and Cultural Heritage Fund through the Minnesota Historical Society.

Scanning Responsibility

Northern Micrographics

Date Digital

2019-06-24 00:00

Metadata Creation Responsibility

Anna Gaffey

Unique Identifier


Synchronous emergence of Hexagenia bilineata mayflies in the laboratory



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