On the responses of the african migratory locust to different types of background

Abstract

It is known that the hoppers (or immature forms) of certain species of locusts, in the solitary phase, bear a marked colour resemblance to the immediate environment in which they are living. They are, for example, green when living among fresh green vegetation, light brown on sand, speckled greyish white on white limestone rocks, and so on. Faure (1932) conducted a series of experiments with Locustana pardalina (Walk.) and Locusta migratoria subspecies migratorioides R. and F. in South Africa. His object was to discover whether there was only a coincidence between the prevailing coloration of the hoppers of these two species and that of their environment, or whether a genuine colour adaptation is involved. He isolated a number of young hoppers, of the same stock, placing each insect in a separate wooden box, provided with a sliding glass lid and reared it to the adult instar. The wood of each box was painted on the inside with ordinary commercial oil paints and, when dry, the latter were compared with the coloured plates of Ridgway (1912) and named according to the tints which they resembled most closely. The experiments of Faure were done out of doors, and he recorded the general coloration assumed by each locust during and at the end of the experiments, noting them as “good”, “fair”, “slight” or “none”, according to the degree of resemblance their coloration bore to that of the insides of the boxes. He obtained a majority of “good” or “fair” resemblances on white, black, grey, yellow and brown backgrounds in the boxes, and one striking resemblance on a black and white striped background. No resemblance occurred when confined in boxes painted green, pink, blue, or with black and orange stripes. Faure also carried out some other experiments on a smaller scale, such as using glass lids of the colours resembling those of the walls of the boxes, but these, as he states, were, on the whole, inconclusive. He brought forward evidence, however, of great importance as regards the production of green hoppers. These, he found, did not result in response to a green background and were only produced in the presence of a moist atmosphere and an abundance of succulent food. He further showed that the green colour-producing substance was spectroscopically very different from chlorophyll, and prepared extracts showed none of the characteristic fluorescence. The present paper describes experiments which have been made with a view to determining the relation between the general coloration of the hoppers and the wave-lengths of the effective colours forming different backgrounds.