Prothoracic Gland and Gregarious Behaviour in Locusts

Abstract

LOCUST hoppers of the gregarious phase are attracted towards one another and so form groups. Such social aggregation depends on learned reactions and is not shown by hatchlings or by individuals which have lived in isolation (solitary phase). In contrast, the vigorous marching shown by bands of gregarious locusts is not learned and is exhibited in a lesser degree by solitary hoppers¹. The amount of marching is related to the general level of activity of the animal and is greater in larger than in smaller groups of hoppers. Not only does the vigour of marching depend on the degree of crowding of the hoppers, but also on the history of their parents. The offspring of crowded parents march more vigorously than those from isolated parents².