The quantitative analysis of climate in relation to insect abundance

Abstract

(1). All natural complexes are related, directly or indirectly, through climate. The importance of quantitative methods of evaluating the role of various climatic factors is, therefore, apparent.(2). In addition to a pronounced seasonal rhythm in abundance, plagues and dearths of insects come and go with considerable regularity, when viewed over a series of years. The most important period is one of approximately eleven years, with a tendency to mass periodicity during the years closely following the epoch of sunspot-minima.(3). Insect -populations are controlled by a complex of continually varying environmental factors, of which the climatic ones assume the dominant r6le in the causation (but not always the termination) of insect - outbreaks.(4). There are great differences in the relative susceptibility of the different phases of the life-cycle to environmental conditions, so that critical periods can be recognised. As the latter are usually restricted to a few days or weeks associated with reproduction or the early stages of existence, and the damage is caused by a more mature stage, the weather during the critical periods has a high predictive value.(5). Insect-outbreaks result from an unusual combination of circumstances during a particular period. These 'optimum' conditions are widely separated in space and time, so that the environment normally imposes control, and outbreaks mean escape from control - an abnormal phenomenon.(6). In addition to the academic interest of the results, particularly in relation to the equilibrium of Nature, it is believed that they may have considerable economic value, by providing a scientific basis for the prediction of outbreaks.