The Phases of the Rocky Mountain Locust Melanoplus Mexicanus (Saussure)

Abstract

Dr. Faure has shown experimentally (1932) that the brown locust, Locustana pardalina, of South Africa exists under two phases, the solitary phase and the swarm phase. Each of the individuals of the solitary phase, which live in isolation like most common grasshoppers, is a representative form of the phase solitari-r. Each of the individuals of the swarm phase, which come together in great dense swarms and then migrate over the country, is a representative of the phase gregari-r. The nymphs of the phase gregaria differ markedly from the nymphs of the phase solitaria in coloration, while the adults of gregaria differ in several morphological characters from the adults of the phase solitaria. Dr. Faure, by means of an ingenious series of experiments, has been able to transform the progeny of the solitaria phase into the phase gregaria. There is, therefore, now no doubt of the fact that the transformation of this grasshopper from one phase into the other phase occurs in nature when the conditions are present to bring it about. It has been suggested recently by several authors that our Rocky Mountain locust Melan-oPlus spretus, now apparently extinct, was the long winged migratory (gregaria) phase of our common grasshopper Melan-oplus (atlanis) mexican-us. Dr. Faure conceived the idea of attempting, by his experimental methods used so successfully with the brown locust of South Africa, to transform M. mexican-us which he surmised to be the solitaria phase into M. spretus, the phase gregaria. The following paper embodies the results of Dr. Faure's observations on M. mexican-us in rearing experiments carried out at Saint Paul, Minnesota, during l\'lay, June, and July 1932.