ECOLOGICAL STUDY FOR CIRCADIAN CLOCK-ANALYSIS OF ADAPTIVE SIGNIFICANCE OF ECLOSION TIMING AND LOCOMOTOR ACTIVITY RHYTHMS

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For the insects pupating in the soil, the day-night temperature cycle may provide a primary time cue (Zeitgeber) for adult eclosion to occur at an appropriate time of the day. In the soil, however, the phase of temperature cycle is delayed with depth because of the low heat conductivity of soil. Therefore pupae located deeper in the soil might compensate for the depth-dependent phase delay of Zeitgeber to avoid mistimed emergence. We examined the adult eclosion timing of the onion fly, Delia antiqua, pupating at different depths in soil and under various thermoperiods in the laboratory to determine if such compensation indeed occurs. We found that D.antiqua is able to compensate for the depth-dependent phase delay of the Zeitgeber by advancing the eclosion timing in response to the amplitude of the temperature cycle decreasing with depth.Many dipteran insect emerge as adults in early morning. This trend would be associated with diel change in environmental conditions. One of the well-known hypothesis explaining this phenomenon is that relatively humid and cool air in the morning would favor the wing elongation of newly emerged adults (Pitendrigh 1954). At oresent, however, little is known how desiccation and high temperature disturb the wing elongation of newly emerged flies. To test this hypothesis, influence of humidity and temperature on wing-elongation of D.antiqua was examined. In the temperature range from 20C to 35C, desiccation has no harmful effect on the wing elongation; even if RH fell below 10%, most individuals examined elongated their wings successfully. Contrast to humidity, high temperature disturbed the wing-elongation considerably. Thus, avoidance of mid-day high temperature would be at least in part involved in the adaptive significane of early morning adult eclosion.