An Analysis Of Pre-Flight Warm-Up In The Sphinx Moth, Manduca Sexta

Abstract

ABSTRACT The physiology of pre-flight warm-up in Manduca sexta was analysed with regard to rate of heat production, regional partitioning of heat between thorax and abdomen, and the control of blood circulation. When moths which have come to equilibrium with ambient temperature undergo pre-flight warm-up, the thoracic temperature increases linearly until flight temperature (37 –39 °C) is approached. The rate of increase in thoracic temperature during warm-up increases directly with ambient temperature from about 2 °C/min at 15 °C to about 7 ·6 °C/min at 30 °C. The temperature of the abdomen remains near ambient throughout the period of warm-up, but during the initial part of post-flight cooling while thoracic temperature declines sharply abdominal temperatures rise appreciably. During warm-up the rate of wing vibration increases linearly with thoracic temperature. At a thoracic temperature of 15 °C the rate is about 8/sec and at 35 °C it is about 25/sec. When resting animals are held by the legs they at once begin to beat their wings through a wide angle. These wing beats at any given thoracic temperature are slower than the wing vibrations characteristic of normal warm-up, but they cause thoracic temperature to increase at almost the normal rate. The removal of thoracic scales causes a decrease in rate of warm-up, but in still air this does not prevent the moths from reaching flight temperature. During cooling the rate of decrease in thoracic temperature is greater in live animals than in freshly killed ones. At any given difference between thoracic and ambient temperatures cooling rates are directly related to thoracic temperature. In resting moths heart pulsations are usually variable with regard to rate, amplitude, rhythm, and sometimes direction, but the records of cardiac activity simultaneously obtained from thorax and abdomen show close correspondence. During warm-up the records of changes in impedance from electrodes in the abdomen indicate that pulsations of the abdominal heart are either absent, greatly reduced, or at a frequency different from that simultaneously recorded from the thorax. The calculated rate of heat production during warm-up is linearly related to thoracic temperature. Our data are consistent with the assumption that heat produced in the thorax during warm-up is sequestered there by reduction in blood circulation between thorax and abdomen. Rates of warm-up in insects are close to the values predicted on the basis of body weight from data on heterothermic birds and animals.