The nervous system of holometabolous insects directs the behaviour of three radically different stages, the larva, pupa and adult. In some cases, larval neurones degenerate during metamorphosis and are replaced in the adult by neurones derived from retained embryonic neuroblasts1,2, but many larval neurones are retained and undergo a morphological and synaptic reorganization which allows them to perform new functions in the adult 3,4. This cellular rearrangement, however, creates a problem in that the developing adults continue to display pupal-like behaviour even after the neurones attain their adult form. We show here that in the tobacco hornworm, Manduca sexta, the adult function of a neurone is prevented from being expressed precociously by the persistence of inhibitory influences that are removed abruptly at adult emergence.
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