Factors Altering Spiracle Control in Adult Dragonflies: Water Balance

Abstract

Dragonflies caught in the wild display a marked variation in the degree of control exercised over their spiracles. In the laboratory desiccation produces tighter control and hydration looser control of spiracle 2: that is, in a partially desiccated insect the thresholds of the spiracular responses to carbon dioxide and to oxygen lack are raised. In desiccated insects the frequency of motor impulses to the spiracles is higher than in hydrated individuals. These effects can be reproduced by perfusion with physiological salines of various strengths. The reaction does not depend on the osmotic pressure of the solution but on the concentration of one or more of its constituents. The isolated mesothoracic ganglion is able to mediate this reaction.