ENDOTHERMY AND FLIGHT THRESHOLDS FOR HELICOVERPA-PUNCTIGERA AND HELICOVERPA-ARMIGERA (LEPIDOPTERA, NOCTUIDAE)

Patterns of endothermic warm-up and flight thresholds were determined for Helicoverpa punctigera and H. armigera. Both species utilise endot hermic mechanisms of heat gain to raise thoracic temperature (T(th)) t o a level at which flight is possible. Endothermic warm-up, accomplish ed by wing shivering, was possible from a minimum of 3-5-degrees-C. Ti me taken to warm-up is inversely related to ambient temperature (T(amb )). At T(amb) higher than 28-degrees-C, flight was spontaneous. At T(a mb) of 10-25-degrees-C, both species maintain T(th) of 20-30-degrees-C during flight. During free flight both species display independence o f T(th) from T(amb) and a narrowing of the thoracic excess (T(exc)) wi th increasing T(amb). Tethered-flight methodologies are intrusive on n ormal thermoregulatory balance, manifested as increased dependence Of T(th) on T(amb). Thoracic scales act as thermal insulation, removal of scales acts to increase thermal conductance. Warm-up for both species is energetically more expensive at low T(amb) than at high T(amb). Th e increased energy requirements for warm-up at low ambients may limit the frequency of warm-up and flight.