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Journal of Experimental Biology 93,51-63 (1981)
Published by Company of Biologists 1981

A Hormone Effecting Immobilization in Pupariating Fly Larvae

JAN ZDAREK ¹, REBECCA ROHLF ², JIM BLECHL ², and GOTTFRIED FRAENKEL ²

¹ Department of Entomology, University of Illinois, Urbana, Illinois 61801, U.S.A.; Institute of Entomology, CSAV, Department of Insect Physiology, Papirenska 5, Prague 6, Czechoslovakia
² Department of Entomology, University of Illinois, Urbana, Illinois 61801, U.S.A.

The haemolymph of 1-2 h old (orange) puparia of Sarcophaga bullata contains a factor (PIF) which immobilizes mature fly larvae, most strongly 6-24 h before pupariation. It has all the properties of a protein: a mol. wt. of between 100 000 and 300 000 daltons, it is heat labile, non-dialysable, destroyed by trypsin, and precipitated by NH₄SO₄. It is possibly identical with the anterior retraction factor (ARF) because the activity of both always went hand in hand. Its action seems to be unspecific in cyclorrhaphous flies. Much about PIF has been learned from studying changes in internal haemolymph pressure of larvae injected with PIF before and during pupariation. Its function is probably to shut off muscular activity after the puparium is completed. It may also function in very small dosages at the beginning of pupariation when the activity of the larvae decreases.