Effects of Photoperiod and Thermoperiod on Hatching Rhythm in Homorocoryphus jezoensis Matsumura et Shiraki (Orthoptera: Tettigoniidae)

When eggs of Homorocoryphus jezoensis were kept under 12L : 12D at 30, 25 or 20 degree C, nymphs hatched 6-10 h after light-off. Under continuous darkness (DD) or light (LL) at 25 degree C, hatching was not synchronized. When exposed to various photoperiods of 24 h cycle at 25 degree C, however, eggs mainly hatched at around light-on with photophases longer than 16 h. With photophases shorter than 12 h, eggs hatched during the darkphase, and the mean hatching time (light-off=hr 0) tended to be later as the photophase was shortened. Under thermoperiodic conditions (with 12 h each of warm and cool phases) in DD or LL, eggs hatched 6-10 h after temperature fall. Under a combination of photoperiod (12L : 12D) and thermoperiod (25 degree C : 20 degree C, each 12 h), hatching time basically depended on the photoperiod. Under the treatments with an un-naturally large phase angle between thermoperiod and photoperiod, however, their interacting effect was observed. When eggs were transferred to constant conditions from photoperiodic or thermoperiodic treatments, the hatching rhythm continued and it showed the circadian rhythm.