Endocrine Mechanisms Controlling Phase Polymorphism and Body-color Polymorphism in Locusta migratoria

The migratory locust,Locusta migratoria,occurs in two extreme phases,solitarious and gregarious,with intermediate forms in between.Solitarious and gregarious individuals look so different in morphological,physiological,behavioral traits,and body-color that they had been regarded as two different species until Uvarov (1921) formulated the phase polymorphism theory.In this locust,the juvenile hormone is responsible for the induction of green color in solitary hoppers.In recent studies,a dark-color inducing neuropeptide,His7-corazonin,was isolated and identified from the corpora cardiaca (CC) of locusts through a convenient bioassay using an albino mutant of L.migratoria.Albinism in this mutant is controlled by a single recessive Mendelian unit and it is caused by an absence of His7-corazonin from the brain and the CC.Injection of His7-corazonin into nymphs caused them to develop various non-green colors,such as fawn,brown,reddish-brown,black (solitarious body-color) and black patterns with an orange background color (gregarious body-color).Injection of His7-corazonin into isolated-reared nymphs caused a shift in morphometrics towards values typical for gregarious insects.Those studies provide strong evidences for an important role of His7-corazonin in the control of phase polymorphism in L.migratoria.