The retardation of puparium formation in Diptera: could factors other than ecdysone control cuticle stabilisation in Glossina and Sarcophaga species?

Abstract

Evidence gained using blowflies (Calliphora vicina R.-D., Lucilia sericata (Mg.), L. cuprina (Wied.) and Protophormia terraenovae (R.-D.) ), fleshflies (Sarcophaga spp.) and tsetse flies (Glossina spp.) in ligaturing experiments and by the injection of prepupal haemolymph (with added ecdysone) suggests that factors other than ecdysone, released in the posterior segments, may initiate pupariation. They could act as synergists for ecdysone. Puparium formation is reduced from 77·5±3·1% to 35·7±2·8% (PSarcophaga argyrostoma (R.-D.) larvae instead of into the abdomens of singly tied larvae. The pupariation score is increased to 57·2±4·8% if haemolymph from rounded-off prepupae is injected into the middle region of isolated abdomens. The uninjected posterior region sometimes darkens alone. Ligature of the abdomens of S. peregrina R.-D. and S. argyrostoma prepupae which have just reached the orange-peritreme stage before rounding-off confines the pupariation to the posterior segments.The effects of retarding puparium formation for 12–24 h by the use of dopa decarboxylase inhibitors or by means of a loose constriction (‘ cummerbund‘) are reported because the location of the patches of cuticle which stabilise and darken as the inhibition slowly wears off implicates certain areas under the integument as the sites of production or secretion of puparial tanning hormone or ‘ posterior darkening factor ’. Retardation of pupariation results from the pressure stimulus applied to rounded-off prepupae because either a hormone is held back or an inhibitor is released as a consequence of the distortion of the cuticle by the cummerbund. When fleshfly larvae are tightly ligatured every hour in front of or behind the brain for 18 h after removal from a moist environment which inhibits pupariation, the percentage of larvae which pupariate in both situations suggests that the CNS itself can inhibit pupariation of the anterior region because of the presence of the stricture. This inhibition, which is not due to lack of oxygen, can be reversed by the presence of factors produced in the abdomen.