Studies on the relationships between air temperature and the internal body temperature of Locusta migratoria

Abstract

Changes in the body temperature of Locusta migratoria L. when the air temperature around it was slowly increased have been recorded. The responses found varied according to the physiological condition of the insect. In normal insects the body temperature showed an initial lag of about 1·4°C behind that of the air. After the first 15 min the body temperature increased at the same rate as the air temperature. When changes in air temperature were stopped, the body temperature still increased and showed a temperature excess of about 0·5°C above that of the air. Experimental technique precluded the possibility of this being due to radiant heat, exercise, or conduction from hotter objects. Normally, the locusts were brought into equilibrium with a temperature of, or just above, 20°C. If, however, they were equilibrated with a lower temperature (15°C), then the response curve showed a greater lag lasting for a longer time followed by a body temperature increasing more rapidly than the still increasing air temperature. The final overshoot was not so large and was present in only 60 per cent of the animals tested. Starved locusts were incapable of increasing their body temperatures at a rate greater than that of the air and showed a continually increasing depression until the air temperature was held steady. There was no overshoot at the end of the experiment. Injections of sub-lethal doses of potassium cyanide had a similar but less severe effect. Injections of 2 : 4-dinitrophenol (DNP) did not increase the body temperature in a constant environment of 20°C. It had a most marked effect when the air temperature was increasing, the response curve immediately after the initial depression showing a rate of increase in body temperature in excess of that of the air. The body temperature actually exceeded that of the air whilst the air temperature was still increasing. The final overshoot was about 1°C. The possible causes of these different response curves are discussed. It is thought that they cannot be explained on the assumption that body temperature depends solely upon the absorption of heat from the air with its consequent stimulation of metabolism. But, that the air temperature through the stimulation of temperature receptors causes the release of substances into the haemolymph which stimulate metabolism, and that part of the increase in body temperature results from this. The mechanism may be important in that it enables the insect to reach equilibrium conditions with its environment more quickly than it could in its absence. It also enables the insect to speed up its development by allowing the maximum use to be made of transient increases of air temperature themselves too feeble to warm the mass of the locust.