Temperature Regulation of the Sphinx Moth, Manduca Sexta: II. Regulation of Heat Loss by Control of Blood Circulation

1. The circulatory anatomy of Manduca sexta is such that heat loss from the thorax is minimized when the flow of blood is reduced, and maximized when it is increased. 2. Abdominal temperatures immediately after flight suggested that blood flow was substantially increased during flight at high TA, and greatly reduced during flight at low TA. 3. When the thorax was artificially heated, the pulsation rates of the abdominal blood vessel increased, the amplitudes of the pulsations became large, and the pulsations were always in the posterior-anterior direction. 4. Heating of the abdomen often resulted in the constriction of the abdominal vessel and a reduction in the amplitude of the pulsations. 5. Transection of the ventral nerve cord reduced the frequency of the high-amplitude pulsations and abolished the ability of the abdominal heart to respond to thoracic heating. 6. When the heat was applied to the thorax, but not to the abdomen: (a) TTh increased while TAb remained near TA; (b) TAb then increased while TTh stabilized near 40-42 °C; (c) finally, if the heat input was not excessive, TAb also stabilized at a temperature above TA. 7. Neither stabilization of TTh nor increase of TAb were observed during thoracic heating of dead moths or those with transected nerve chords. 8. The distribution of temperature observed in the abdomen during thoracic heating is not explicable in terms of heating by conduction from the thorax. 9. During modest thoracic heating, decreases of TTh were correlated with intervals during which there were full-length pulsations of the dorsal vessel. During periods where movement of the vessel was observed only at the anterior end of the abdomen, the temperature of the thorax increased. 10. Calculations of blood flow and heat flux indicate that the regulation of TTh in the observed range is physically reasonable by blood circulation alone.