ACTIVATION OF PHOSPHORYLASE IN RESPONSE TO COLD AND HEAT-STRESS IN THE FLESH FLY, SARCOPHAGA-CRASSIPALPIS

Glycogen phosphorylase can be activated in diapausing pupae and nondiapausing pharate adults of the flesh fly, Sarcophaga crassipalpis in response to both cold and heat stress. The greatest activation was observed at 0 and above 30°C. Activation was rapid: following exposure to 0°C activated phosphorylase increased 36-58% within 30 min. The proportion of activated phosphorylase was consistently lower in diapausing pupae than in nondiapausing pharate adults. Among the nondiapausing stages, only pharate adults and adults responded to cold stress (2 h at 0°C) and heat stress (2 h at 40°C) by activating phosphorylase. No such response was observed in larvae or young pupae. During diapause, the proportion of activated phosphorylase was highest at the onset of diapause, declined and remained fairly constant throughout the remainder of diapause. Diapausing pupae held continuously at 0°C maintained a higher proportion of activated phosphorylase throughout the diapause than pupae held at 20°C. Cold stress consistently activated phosphorylase in diapausing pupae held at 20°C, but heat stress elicited this response only during the last half of diapause. The activation of phosphorylase by brief periods of chilling and the activation observed in diapausing pupae held continuously at low temperature is consistent with our earlier work showing an elevation of glycerol under these conditions. © 1990.