Thermoperiodic Effects on the Regulation of Larval Diapause in the Tufted Apple Budmoth (Lepidoptera: Tortricidae) 1

Abstract

Combinations of photoperiods and thermoperiods strongly influence the induction of larval diapause in the tufted apple budmoth, Platynota idaeusalis (Walker). Photoperiodic effects may be intensified when the cryophase of the thermoperiod coincides with scotophase of the photoperiod, or the effects may be reduced when the thermophase occurs during scotophase. Photoperiodic and thermoperiodic interactions may be nullified by either a thermoperiod with a high temperature cycle (36:24°C) or a cryophase (15°C) duration of <11 h, even though it coincides with scotophase. Under continuous illumination or darkness, thermoperiods with half cycles of 12 h and 4°C temperature range (23:19°C) to a 16°C temperature range (29:13°C) failed to induce diapause. Larval exposure to one of a series of 26:16°C thermoperiods in which the duration of the cryophase was increased in 2-h increments from 10 to 20 h in continuous darkness showed that thermoperiod under constant darkness does not induce diapause.