Neural Inhibition of Corpus Allatum Activity during Metamorphos of Periplaneta americana1: a Reassessment

Abstract

All last instars with a severed nervus corporis allati 1 (NCA 1) underwent a supernumerary molt, as did 80–85% of those with one corpus allatum (CA) removed. The sham operation caused an extra molt by 60–85% of the nymphs, but those that were totally allatectomized usually metamorphosed. Apparently, juvenile hormone production by the CA was enhanced or sustained following surgery. The NCA 1 and nervus corporis allati 2 (NCA 2) supplying the right CA were cut immediately after removing the opposite gland. Only supernumerary nymphal molts resulted, suggesting that neither of these nerves provides stimuli necessary for CA activity. Furthermore, the incidence of additional nymphal instars after severing NCA 2 to the remaining gland resembled that obtained after removing the left CA, so NCA 2 does not seem to constitute an important inhibitory pathway. Because CA activity fostered by cutting NCA 1 is neither as site-specific nor as direct as reported previously, it may not reflect the removal of an inhibitory innervation.