The thoracic mechanism for eclosion and digging during the extrication behaviour of Diptera

ABSTRACT. Dipteran flies escape from the puparium by coordinated contractions of all segments of the body. Whereas special eclosion muscles have been identified in the abdomen and head, none has previously been described in the thorax. Three pairs of large thoracic muscles are described in this paper which are involved solely with eclosion. They have ultrastructures consistent with an ability to supercontract and all three degenerate within 48 h following escape from the puparium. Recordings of electrical activity show them to be rythmically active, coincident with thoracic contractions during eclosion. Many of the non-fibrillar flight muscles are also incorporated in the eclosion motor pattern and have a precise sequence of activity. Following escape there is a rapid switch from eclosion to flight motor and this is discussed with reference to afferent mediation and changing inputs to the muscles.