EFFECTS OF TEMPERATURE AND COLD STORAGE ON DEVELOPMENT TIME AND VIABILITY OF EGGS OF THE BURROWING MAYFLY HEXAGENIA RIGIDA (EPHEMEROPTERA: EPHEMERIDAE)

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Abstract
Eggs of Hexagenia rigida McDunnough transferred directly from 20° to 36°, 32°, 28°, 24°, 20°, 16°, 12°, and 8 °C were monitored for start of hatch, hatching rate, success of hatch, and hatching period. Eggs did not hatch at 36 °C or 8 °C. There was a direct relationship between temperature and start of hatch (from day 7 at 32 °C to day 77 at 12 °C). Over 90% hatch occurred at all temperatures except 12 °C. Hatching periods ranged from about 6 days at the higher temperatures to over 80 days at 16 °C and 12 °C. Hatching occurred at 36 °C when eggs were transferred in increments of 4 °C every 2 days.Storage capabilities of eggs in "early", "middle", and "late" stages of embryonic development were tested at 12 °C and 8 °C using a direct or stepwise transfer method. Hatching parameters monitored were hatch rate, success of hatch, and hatching period up to 90% hatch of total number of eggs. Middle stage eggs transferred in a stepwise manner could be held at 8 °C for up to 52 weeks with least effect on hatching parameters. Middle and late stage eggs could be stored for up to 16 weeks at 8 °C using the direct transfer method, and early stage eggs, which were affected most by cold storage, could be held for 2 days at 12 °C with minimal effect on hatching parameters. The storage of eggs, shown here to be possible, is potentially useful for providing such material for bioassays throughout the year.