STRETCH-INDUCED MOLTING IN ONCOPELTUS-FASCIATUS

Fifth instar nymphs of Oncopeltus fasciatus initiate a moulting cycle when they reach a critical weight of 27.9±1.1 (±S.D.) mg for females or 23.7±1.2 mg for males. This critical weight is not absolute. Its precise value depends on the somatic size of the individual. Large-bodied individuals have a higher critical weight than small-bodied ones. Sexual size-dimorphism accounts largely for sex differences in critical weights. Animals of a subcritical weight can be induced to moult by means of a saline injection, in the absence of further food intake or growth. Since a saline injection only stretches the abdominal wall it is suggested that moulting in Oncopeltus is triggered by stimulation of abdominal stretch receptors, as in bloodsucking Reduviidae. The critical weight is thus an index of the size at which a critical degree of stretch is achieved. © 1979.