A New Biometrical Phase Character in Locusts

Abstract

THE solitary and the swarming phases of the same species of locusts can be distinguished by coloration and by biometrical characters¹. Among the latter, the ratio E/F of the elytron length (E) to the posterior femur length (F) has been generally used², but no proper statistical investigation of the relative merits of various measurements and ratios exists. Careful measurements of all suitable parts of the body have now been undertaken on samples of the desert locust, Schistocerca gregaria (Forsk.), taken from wild populations of a very low density (phase solitaria), and from swarms (phase gregaria), and the data analysed statistically. None of the twenty direct measurements of body parts proved to be suitable, as the frequency distribution polygons for the two phases overlapped widely. The E/F ratios also showed an overlap which made its use uncertain. Moreover, a comparison of E values in the two extreme phases showed that the elytron-length varied, according to the phase, in an opposite direction in the two sexes, thus: