The Life Cycle of the Box-Tree Pyralid, Glyphodes perspectalis (WALKER) (Lepidoptera:Pyralidae): III. Photoperiodic Induction of Larval Diapause

The photoperiodic induction of larval diapause of the box-tree pyralid, Glyphodes perspectalis (WALKER) collected from four localities in Japan showed typical long-day response curves. The critical photoperiods were 14h 20min for the Miyagi and Fukuoka (Mt. Kosho; 862m above sea level) populations, respectively, 13h 50min for the Tokyo-Chiba population and 13h 40min for the Kochi population at 20°C, showing a geographical cline. The critical photoperiods for the photoperiodic response in the offspring of overwintering generation of the Tokyo-Chiba population showed large individual variations. Moreover the critical photoperiod varied with temperature conditions, being higher at 15°C than at 25°C. When reared singly or in a crowded condition on three kinds of host plants, Buxus microphylla, B. sempervirens and B. microphylla var. insularis, their photoperiodic responses were typical long-day types except in the crowded condition on B.m. var. insularis where a high level of diapause was induced even under long-day conditions. This result suggested that dietary conditions were acting as regulating factors of diapause induction. The sensitive period for the photoperiodic induction of diapause lies between the first and third instar, especially the latter half. Photothermographs for four localities suggest the occurrence of two to four generations per year depending on the locality. For the Tokyo-Chiba population the predicted life cycle fitted well with the actual field observations.