Patterns of endothermic warm-up and flight thresholds were determined for Helicoverpa punctigera and H. armigera. Both species utilise endothermic mechanisms of heat gain to raise thoracic temperature (T(th)) to a level at which flight is possible. Endothermic warm-up, accomplished by wing shivering, was possible from a minimum of 3-5-degrees-C. Time 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(amb) of 10-25-degrees-C, both species maintain T(th) of 20-30-degrees-C during flight. During free flight both species display independence of T(th) from T(amb) and a narrowing of the thoracic excess (T(exc)) with increasing T(amb). Tethered-flight methodologies are intrusive on normal 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). The increased energy requirements for warm-up at low ambients may limit the frequency of warm-up and flight.