Haemolymph ecdysteroid titres at metamorphosis in the fruit fly Ceratitis capitata: multiple peaks not apparent in whole body extracts

Abstract. The titre profile of haemolymph ecdysteroids in the fruit fly Ceratitis capitata was constructed from determinations of haemolymph taken from single animals and compared with ecdysteroid levels in whole body extracts. Larvae were sampled throughout the period from the late third instar larva until eclosion and were synchronized using a conspicuous behavioural marker ('leaping') that occurs at the end of the wandering period. Extracts of the whole body exhibit two peaks of ecdysteroids, one associated with pupariation ('pupariation peak' of other authors) and the other with pharate adult development. However, the 'pupariation peak' corresponded with three temporally distinct peaks in the titre of haemolymph ecdysteroids. The first peak occurs at the time of head retraction (lh before formation of the white puparium) and may represent the initial response to release of prothoracicotropic hormone. The second peak occurs 2–3 h later at the onset of tanning and may be responsible for induction of dopa-decarboxylase. These peaks are brief ( c . 2h each), whereas the third is much longer (16 h) and occupies most of the 'pupariation peak'. The first two peaks have not been reported previously in any dipteran. Their existence illustrates that extremely brief pulses of ecdysteroids occur in vivo , apparently with profound developmental consequences. The fact that brief pulses in the haemolymph titre are not apparent in whole body extracts emphasizes that results obtained using the latter method must be interpreted with caution.