Entrainment of the Larval Locomotor Activity Rhythm of a Carabid Beetle, Carabus insulicola insulicola (Coleoptera: Carabidae) to T21 and T24 Cycles and After-Effects on Free-Running Period

Abstract

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 (10.5 h light and 10.5 h 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 (a) beginning a few hours after dusk until the end of the first half of the photophase. When a 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, ψ decreased 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 a 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 (23.4 h) at DD for T21 larvae was significantly shorter than that for T24 larvae (24.5 h). © 1992, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.