HORMONAL CONTROL OF IMAGINAL DISC REGENERATION IN GALLERIA MELLONELLA (LEPIDOPTERA)

¹ Developmental Biology Center, Case Western Reserve University, Cleveland, Ohio 44106

1. These experiments examined the mechanism whereby regeneration delays development and molting in the waxmoth, Galleria mellonella, and also the possible role of the molting hormone in controlling regeneration.

2. Removal of one or more imaginal wing discs from four-day old last instar larvae delayed the further development of unoperated discs and the pupal molt, confirming prior observations on Ephestia, Blattella and Periplaneta by other workers. The delay in molting was proportional to the amount of regenerating tissue: extirpation of one wing disc caused a five-day delay, whereas extirpation of all four discs caused a 14-day delay. When time regenerating epithelium was destroyed by cautery, no delay in molting occurred. Several possible mechanisms for this delay were examined.

3. In another series of experiments four-day old last instar larvae were ligated in such a way as to eliminate both brain and prothoracic glands. When imaginal wing discs were extirpated from these ligated larvae 0 to 14 days after ligation, the percentage of larvae in which the imaginal discs regenerated decreased from 75% to 10%. This defect was repaired by injecting 10 µg/gm of a synthetic molting hormone, alpha ecdysone, immediately after extirpating the wing disc. This treatment enabled the larvae to regenerate the missing disc.

4. It is concluded that regeneration of imaginal discs in Galleria requires ecdysone.

5. Additional experiments indicated that ecdysone promoted regeneration only within a certain range of concentrations: a concentration of 10 µg/gm promoted regeneration whereas 100 µg/gm promoted the prompt secretion of cuticle and blocked regeneration.

6. Ecdysone was less effective in promoting regeneration if the wound healed before it was applied. Thus injecting 10 µg/gm immediately after wing disc extirpation promoted regeneration, whereas an identical injection 24 hours after extirpation failed to promote regeneration. This suggests that injured tissues may be more sensitive to ecdysone.

7. Arguments were advanced that ecdysone promoted regeneration of Galleria wing discs directly by acting on the imaginal discs themselves and perhaps indirectly by promoting the growth of the tracheal system.

This article has been cited by other articles:

				L. Cherbas, X. Hu, I. Zhimulev, E. Belyaeva, and P. Cherbas EcR isoforms in Drosophila: testing tissue-specific requirements by targeted blockade and rescue Development, March 2, 2003; 130(2): 271 - 284. [Abstract] [Full Text] [PDF]

				D. L. Mykles Interactions Between Limb Regeneration and Molting in Decapod Crustaceans Integr. Comp. Biol., June 1, 2001; 41(3): 399 - 406. [Abstract] [Full Text] [PDF]

				D. J. Emlen Costs and the Diversification of Exaggerated Animal Structures Science, February 23, 2001; 291(5508): 1534 - 1536. [Abstract] [Full Text] [PDF]