The physiology of wandering behaviour in Manduca sexta. I. Temporal organization and the influence of the internal and external environments.

A stereotyped series of behavioural changes occurs in preparation for pupation in Manduca sexta. Feeding declines over an 8-h period, after which the larva coats its body with a labial gland secretion. The animal then begins a 10- to 30-h wandering behaviour during which it constructs a pupation chamber underground. Wandering behaviour starts during a specific temporal gate which is determined by an internal circadian timer. The scotophase of the day prior to wandering has the major influence on the timing of internal processes which activate the behaviour. Wandering duration is correlated with larval size, reflecting a possible influence of juvenile hormone. The larva appears to be irrevocably committed to begin wandering by an event that occurs about 15 h previously, a time that corresponds to the second of three prothoracicotropic hormone (PTTH) pulses and the accompanying elevation of ecdysteroids as measured by Gilbert et al. (1981). We conclude that both the initiation and duration of wandering behaviour are governed primarily by processes which are internal to the larva.