Grasshopper populations and weather: the effects of insolation on Chorthippus brunneus

In nature, the internal body temperature of Chorthippus brunneus Thunberg is found to be raised substantially under the influence of direct insolation. In the laboratory, similarly raised body temperatures, resulting from the radiant heat of a light bulb, lead to a 5.6‐fold increase in the rate of development, and a similar or even higher increase in the rate of adult maturation. The rate of egg‐production is even more greatly affected, being negligible in the absence of a radiant‐heat source. These physiological results provide an explanation for the frequently found correlation between grasshopper abundance and hot and/or dry weather. The results are also discussed in terms of the problems they pose for the derivation of a physiological time‐scale for basking insects, and the evolutionary forces and constraints that might give rise to them.