Abstract
Final (fourth) larval instars of Chaoborus americanus Johannsen overwinter beneath the ice of Nearctic ponds. These larvae are developmentally dormant but otherwise active; the maintenance and termination of diapause is known to be mediated by photoperiod and the availability of food (Bradshaw 1969). The control of the initiation of diapause has now been examined. It became possible to carry out this study when samples from George Pond on the University of Michigan's E. S. George Reserve yielded numerous early instars of C. americanus on May 1, 1970.

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