Accelerating and Inhibiting Effects of Crowding on Sexual Maturation in Two Species of Locusts

Abstract

ISOLATED pairs of Locusta migratoria (R. and F.) kept in optimum laboratory conditions may begin to copulate seven days from their emergence as adults, and the majority of females lay their first egg-pods before the 14th day of adult life¹. Isolated pairs of Schistocerca gregaria (Forsk.) kept in the same conditions seldom copulate or oviposit before the fourth week of adult life, and maturation is frequently delayed for long periods². Crowding accelerates maturation in Schistocerca but retards it in Locusta. This difference between two acridids of similar gregarious habit seemed anomalous. However, the observation that continuous crowding of Schistocerca with very young individuals, or fledglings, less than 8 days old retards maturation suggested that the difference between the two species might be mainly one of timing³. This suggestion is confirmed by the results of the following experiment which show that in Locusta, as in Schistocerca³, mature males exert an accelerating influence on the maturation or readiness to copulate of young males.