The emergence, or eclosion, of large moths from the confines of the pupal case has been shown to be initiated by a blood-borne factor, the eclosion hormone (Truman and Riddiford 1970; Truman 1971). The release of this neurohormone into the blood is a vital link in a chain of events that leads from a circadian clock, located in the brain (Truman 1972), to the performance of a stereotyped sequence of behaviors that effect the moth’s escape from the old cuticle (Truman 1971). Thus, the brain clock (which in turn is entrained by environmental variables) is able to determine the time at which eclosion occurs by controlling the release of the eclosion hormone. Once the hormone appears in the blood, eclosion inevitably follows. In the Saturniid silkmoths, the interval between eclosion hormone release and the performance of eclosion behavior is relatively invariant (Truman 1971; 1973a); in Manduca sexta (a Sphingid), on the other hand, the actual initiation of eclosion behavior once eclosion hormone has been released is somewhat subject to the influence of environmental variables (Reynolds et al, 1979).
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