Physiological Control of Molting in Insects

SYNOPSIS. The initiation of a molting cycle in insects is neithera random nor a strictly periodic event. Insofar as molting canaccomplish different things under different circumstances, suchas a change in size or a change in form, it is reasonable toasume that the timing of a molt must be adapted to these functions.The onset of a metamorphic molt, in particular, must be preciselycontrolled because the onset of metamorphosis terminates thegrowth phase of a larva and establishes the body size of theadult insect. This aspect of the control of molting has receivedrelatively little attention and our knowledge of specific physiologicalmechanisms for the control of molt initiation is restrictedto three species: the blood-sucking bug, Rhodnius prolixus,the greater milkweed bug, Oncopeltus fasciatus, and the tobaccohornworm, Manduca sexta. The present review discusses the stateof our knowledge about the factors that render these insectscompetent to molt and about the stimuli that serve as a directtrigger for molting.