Endocrinology Abstracts

The role of moulting hormone in determination of pupariation behaviour in flies

J. Zdarek & P. Myska

Inst. of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo nam. 2, CZ-166 10 Prague 6, Czech Republic

The moulting hormone ecdysone was originally isolated and identified using a bioassay based on the ability of the hormone to induce sclerotisation of pre-critically ligated hind parts of a blow fly larva (Calliphora-test). Later it was found that the hormone injected into non-ligated third instar larvae accelerated the whole process of puparium formation (pupariation), including cuticular tanning and behaviour responsible for attaining the proper shape of the puparium (i.e. frontal retraction and longitudinal body contraction). It was also observed that younger, 20-hydroxy-ecdysone-treated larvae, although perfectly tanned, did not form puparia of normal shape suggesting that pupariation behaviour could not properly be performed. Such a disparity may mean that the cuticular and neural responsivenesses to the hormonal stimulus have different commitment periods. Here we analyse this hypothesis in the flesh fly, Sarcophaga bullata. Our aim was to determine the time of commitment to pupariation of the neural motor centres by monitoring pupariation behaviour of the third instar larvae that had been stimulated to pupariate precociously by various doses of 20-hydroxyecdysone during feeding and post-feeding (wandering) periods. We have confirmed earlier findings that only a short feeding period (12 h) in the third instar is needed for determination of metamorphosis. Larvae removed from food after they had consumed a critical amount formed miniature puparia of normal shape, however after a prolonged period of wandering. At any time during that period they could be induced to pupariate precociously by the injection of 20-hydroxyecdysone. Puparia injected earlier remained larval in shape, indicating that only the cuticular aspect of pupariation was stimulated. Complete performance of pupariation behaviour was recorded only in larvae injected later, during the extended wandering behaviour. This indicates that the appropriate motor neurons acquire competence to initiate pupariation behaviour considerably later than the integument becomes committed to sclerotisation. The effective dose (ED50) of the hormone progressively decreased with increasing amount of food consumed.

Index terms: Sarcophaga bullata, ecdysterone, metamorphosis, motor centres

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