Do the brains of wax moth larvae secrete an allatotropic hormone?

The hypothesis that the brains of young, last instar larvae of Galleria mellonella (L.) initiate supernumerary larval apolyses by secreting an ‘allatotropic factor’ was reexamined. It was confirmed that following bilateral allatectomy the larvae lose their ability to produce supernumerary instars (superlarvae) in response to implanted brains. The JH analog Altosid caused the allatectomized larvae to undergo extra apolyses irrespective of whether or not brains had been implanted. Although the percentage of superlarvae obtained following Altosid treatment was not increased by the implanted brains, the onset of extra apolyses was accelerated. This suggests that the brain can promote larval-larval apolyses without acting first on the corpora allata (CA). Presumably, it does so by producing prothoracotropic hormone.The propensity to generate new larval structures was tested by injecting ecdysterone into larvae 48 and 65 hr after they had been allatectomized. Within 48 hr after both CA had been removed the precocious apolysis resulted in individuals with antennae that were partly larval and partly pupal, and by 65 hr the ability to reproduce larval parts had diminished further. Those that were hemi-allatectomized did not demonstrate this impairment. The results were consistent with the interpretation that allatectomy abolishes the capacity to produce superlarvae because the JH titer declines to a level insufficient to permit expression of the larval genetic program during the next moulting cycle. This is offered as an alternative to the hypothesis that allatectomy prevents implanted brains from producing superlarvae because the target organs of the ‘allatotropic factor’ have been removed.An attempt was made to confirm the observation that brains from young, last instar larvae are more effective initiators of supernumerary apolyses than those from donors in the process of pupating. There was no evidence for a different endocrine function by the brain during the two stages.