A PERSISTENT DIURNAL RHYTHM IN CHAOBORUS LARVAE. I. THE NATURE OF THE RHYTHMICITY1

Abstract

Larvae of Chaoborus punctipennis Say (Diptera: Culicidae) were maintained under constant conditions in two 152‐ × 10‐cm columns containing lake water and sediments. Visual counts of the larvae in the columns were made hourly with a flashlight equipped with a red filter and darkened reflector. Activity was observed during dark periods; however, no activity was observed during light periods. A diurnal rhythm of activity persisted up to 10 days in constant darkness. The phase of the rhythm was reset by entrainment under differing light regimes, as well as by temperatures of 5C or less. These critical low temperatures also abolished activity. The offset of light was demonstrated to be the Zeitgeber for this rhythm; therefore it is necessary that under natural conditions these larvae receive some offset stimulus from the setting sun.