HORMONAL FACTORS IN THE CNS AND HEMOLYMPH OF PUPARIATING FLY LARVAE WHICH ACCELERATE PUPARIUM FORMATION AND TANNING

¹ Department of Entomology, University of Illinois, Urbana, Illinois

1. Hemolymph or central nervous system (CNS) homogenates from Sarcophaga bullata larvae in various stages during puparium formation were injected into red-spiracle larvae (due to pupariate within a few hours), where they cause an acceleration of pupariation. The predominant effect of CNS is on puparial contraction and tanning, and that of hemolymph on retraction of the anterior end.

2. The activity of CNS-preparations changes little from the mature larva through the 24-hours puparium stage. The activity in the hemolymph is absent up to 4 hours before pupariation, at a peak from the white puparium through 4 hours later and then declines. Sixteen hours after pupariation the effect on retraction has disappeared, while that on contraction and tanning is still considerable

3. The active substances in CNS and hemolymph which accelerate retraction or contraction/tanning are not identical and have been designated as X_r and X_t, respectively.

4. Both X_r and X_t can appear in the blood in the absence of the CNS, viz. in the hind part ligated after the critical period, or ligated before that period and injected with ecdysone.

5. The X-factors in CNS and hemolymph are of the nature of proteins. They are denatured by heat, alcohol, or acetone, precipitable by TCA and (NH₄)₂SO₄, non-dialyzable, and destroyed by trypsin or pronase (tested only for CNS).

6. These observations fit a scheme whereby ecdysone causes the appearance and/or accumulation of the X-factors in some tissue and their ultimate release into the hemolymph where they induce pupariation. A product of neurosecretion in the CNS accelerates the release. An alternative explanation assumes that the X-factors originate as a neurosecretion which is stored in the peripheral axons or synapses prior to their release into the hemolymph by the action of ecdysone.