Adult eclosion timing of the onion fly, Delia antiqua, in response to daily cycles of temperature at different soil depths.

For 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 the soil. Therefore pupae located deeper in the soil may 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.