Dormancy in Lymantria dispar (Lepidoptera: Lymantriidae): Analysis of Photoperiodic and Thermal Responses

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Abstract
Dormancy in the gypsy moth is a dynamic process characterized by complex and seasonally variable responses to physical factors. At the end of summer and the beginning of autumn, short daylengths play a small, but perceptible role in diapause maintenance in a small proportion of individuals. By comparison, temperature has a much larger role in diapause maintenance and in the timing of postdiapause hatching. Temperatures >;15.6°C decelerate diapause development, and thus maintain diapause, whereas exposure to 5.0 or 10.0°C accelerates diapause development and enhances the incidence, speed, and synchrony of hatching under warm conditions. A small proportion of individuals in some egg masses need not experience low temperature before they hatch; these individuals hatch in the fall. The thermal responses of the larvae within the eggs change as they undergo dormancy in nature; these changes are evident in the temperature-developmental response curves, the lower thermal thresholds and heat units required for hatching, and the relative rates of development under a range of temperatures. The pattern of change in the thermal responses throughout dormancy suggests that as autumn and winter proceed, there is a gradual transition from diapause to postdiapause periods of dormancy. Thermal responses during dormancy vary considerably among egg masses.

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