1992 Volume 36 Issue 3 Pages 169-175
The locomotor activity of individual 3rd (final) instar larva of Carabus insulicola insulicola was recorded by an infrared-beam actograph at 20°C. The larvae were raised under either LD 10.5:10.5 (10.5h light and 10.5h dark, T21), LD 12:12 (T24), LD 14:14 (T28), or constant light (LL) from eggs and placed in the actographs after the second molt. All the T21 or T24 larvae became entrained but T28 larvae did not; half of the T28 larvae showed ‘relative coordination’ and half showed no clear rhythmicity. The entrained larvae had an active phase (α) beginning a few hours after dusk until the end of the first half of the photophase. When α coincided with the photophase, the activity level remained high irrespective of the entrainment status. Phase-angle differences were read between the onset of activity and light-off (Ψon), and between the end of activity and light-on (Ψend). Within the range of entrainment, Ψdecreased as T increased; the mean change in Ψon per hour, expressed as degrees of T cycles, was 9.7°, and the change in Ψend was 17.7°. The length of α was nearly constant at the T21 and T24 entrainments, at T28 relative coordination, and at constant dark (DD) or LL free-running. The free-running period (23.4h) at DD for T21 larvae was significantly shorter than that for T24 larvae (24.5h).
