Correlated effects of ecdysone and neurosecretion in puparium formation (pupariation) of flies.

A neurohormone accelerates the formation and tanning of the fly puparium in the presence of ecdysone. When larvae of Phormia regina are divided by ligation into two parts before the critical period, the hind part remains untanned, unless injected with blood from a pupariating larva. This confirms earlier observations and is in contrast to recent data with another genus. When Sarcophaga bullata larvae are ligated after the critical period, the anterior part starts to tan about two hours before the posterior part. Injecting neurosecretory material from the brain, the pars intercerebralis, or the corpora cardiaca of S. bullata, or from the brain or c. cardiaca of Periplaneta or Pyrrhocoris into the posterior part induces it to tan before the anterior part. Injection of the same material into normal larvae after the critical period similarly accelerates puparium formation and onset of tanning. Injection of ecdysone or ecdysterone does not have these effects. Thus, the neurosecretory material does not act by causing the release of ecdysone from the ring gland and its function is different from that of the classical brain ("activating") hormone. When injected before the critical period together with ecdysone it potentiates the effect of ecdysone. It is suggested that its biological significance is to coordinate puparial contraction and tanning.