Chiasma Frequency and Gregarization in Locusts

Abstract

PHASE transformation of locusts^1,2 is the reversible group of morphological, biochemical, physiological and behavioural changes in locust hoppers or instars and adults, based to a large extent on population density. The transformation to the swarming or gregaria phase occurs in the field when individuals of the grasshopper or solitaria phase congregate in large numbers due to rapid growth of population. The brown locust, Locustana pardalina Walk., is at present in a cycle of intensive gregarization after a period of about seven years of mainly solitaria life. Gregarization started during the summer of 1962–63 in many areas of the approximately 100,000 square miles of the outbreak region in the Karoo plateau, and continued in the formation of swarms over most of the region during early summer of 1963–64. Many of these swarms have consequently passed through at least three generations of gregarization in the field. Through the courtesy of the Locust Control Division our Locust Research Unit has received field collections throughout the past four years so that representative samples of solitaria, congregating populations and swarms with a history of 1, 2 or 3 generations of gregarization have been available.