The implantation of three brains into freshly ecdysed last instar larvae which possess at least one of the two corpora allata induces extra larval development. Implanted brains appear to produce a neurohumoral allatotropic factor.2. Corpora allata seem to be inhibited via their nervous connections 48-60 hours after the last larval-larval ecdysis and become insensitive to the allatotropic factor. Severance of the nerves innervating the corpora allata and adjacent corpora cardiaca induces extra larval development in 7% of the experimental insects and restores sensitivity to the implanted brains in as many as 20%.3. Severance of the nerves to the corpora cardiaca—corpora allata complexes or implantation of corpora cardiaca—corpora allata complexes into allatectomized larvae in some instances causes a considerable prolongation of the last larval instar. It is suggested that disconnection of the corpora allata from the brain partly removes their inhibition and induces secretion of a low titer of juvenile hormone which is then responsible for the delay in pupation.
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Sehnal et al. (1975) studied this question.