Factors influencing the intensity of larval diapause in Ostrinia nubilalis

Abstract

A study was made of the factors determining the intensity of larval diapause in Ostrinia nubilalis. Intensity was measured in terms of the number of days of long-day exposure (8 h dark–16 h light) at 30°C required to evoke a 50% incidence of pupation ( Days to P 50 ) in the experimental cultures. Intensity of diapause was found to be regulated by the duration of the scotophase and the temperature of the diel rearing regime. Rearing temperatures of 25 and 22°C evoked more intense diapause than did 19°C. Within the diel range of scotophase durations, 12 h evoked greater intensity of diapause than did either longer or shorter scotophases. Circadian resonance in the effect of scotophase duration on intensity of diapause was observed at both 22 and 19°C. Intensification of diapause was demonstrated to occur with a rearing temperature of 19°C, but not at higher temperatures (22 and 25°C). Experimental conditions that intensified diapause (increased Days to P 50 ) did not increase the percentage incidence of diapause. No correlation was detected between incidence and intensity of diapause induced by thermoperiodic regimes.