Temperature Regulation of the Sphinx Moth, Manduca Sexta

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.

Nervous control of the heart during thoracic temperature regulation in a sphinx moth

Heating the thorax of the sphinx moth, Manduca sexta, evoked pulsations of the heart in the abdomen. These pulsations were of relatively high rate and amplitude, and traveled from the abdomen into the thorax. While heat was continuously applied exclusively to the thorax, thoracic temperature often stabilized and abdominal temperature increased sharply. Thoracic heating of moths with transected nerve cord, however, did not evoke these responses. It is inferred that the heart in the abdomen responds to overheating of the thorax through neural influence.

Thoracic Temperature Stabilization byn Blood Circulation in a Free-Flying Moth

The sphinx moth, Manduca sexta, maintains its thoracic temperature within a degree of 42 degrees C while in free flight over a range of air temperatures from about 17 degrees to 32 degrees C. Tying off the dorsal vessel abolishes temperature control. Moths with tied off vessels overheat and then stop flying at air temperatures of about 23 degrees C. However, flight at this temperature is possible when the thoracic scales are removed. The mechanism of temperature control involves transfer of the heat produced in the thorax to the blood pumped from the dorsal vessel, and the subsequent dissipation of this heat when the blood returns to the relatively cool abdomen.