Resonance in photoperiodic regulation of larval diapause in Ostrinia nubilalis

Abstract

Nanda-Hamner experimental photoperiodic regimes (Xh dark-8h light, in which X was from 8 to 88 h) were employed to demonstrate circadian resonance in the induction of larval diapause in Ostrinia nubilalis. Measured in terms of per cent incidence of diapause, manifestation of circadian resonance was shown to be dependent upon ambient temperature; resonance was not apparent at a rearing temperature of 30°C, was equivocally detected at 25°C, but strongly manifested at both 19 and 22°C. The period of the circadian resonance was 24 h at each temperature, demonstrating temperature compensation. Circadian resonance was also demonstrated between duration of the scotophase of the rearing regime and the number of days of long days (8 h dark-16 h light, 30°C) required to terminate diapause. Such resonance was detected when the temperature of the rearing regime was either 19 or 22°C, but not at 25°C. The implications of resonance in photoperiodic determination of apparent initial intensity of diapause is discussed briefly.