Role of the Ventral Nerve Cord and Terminal Abdominal Ganglion in the Regulation of Sex Pheromone Production in the Tobacco Budworm (Lepidoptera: Noctuidae)

Abstract

We sought to clarify the role of the nervous system, and its relationship to hormonal regulation, in controlling sex-pheromone biosynthesis in the female tobacco budworm moth, Heliothis virescens (F.). Isolation of the terminal abdominal ganglion (TAG) from the rest of the ventral nerve cord (VNC), or transection of the terminal nerves that extend from the TAG to the periphery, resulted in severe reduction in the production of sex pheromone that normally occurs during the scotophase. The amount of pheromone extracted from the sex-pheromone glands of these surgically manipulated moths, however, was greater than that extracted from glands of normal females during the photophase, a period when pheromone levels are low or undetectable. Injection of an extract of female TAGs into virgin females stimulated production of sex pheromone. Fractionation of extracts of the TAG and of the brain/subesophageal ganglion (Brain-SEG) complex by solid-phase extraction, ion exchange, and reverse-phase liquid chromatography revealed that the TAG contains pheromonotropic peptides with retention characteristics very similar to those of the Brain-SEG. Immunochemical studies showed that the TAG-derived pheromonotropic peptides have some degree of homology, at their C-termini, to the pheromone-biosynthesis-activating neuropeptide of the corn earworm, Helicoverpa zea (Hez-PBAN). Discrepancies between chromatographic properties of Hez-PBAN and the TAG pheromonotropic peptides, however, indicated that the peptides from H. virescens are not identical to Hez-PBAN. Immunocytochemical studies revealed that axons of PBAN-immunoreactive neurons in the SEG project through the VNC and terminate in the neuropil of the TAG. Because the immunoreactivity was not found in nerves or neurohemal organs of the TAG, it is likely that the pheromonotropic peptides in the TAG function within the TAG rather than as neurohormones or peripheral neurotransmitters. It is not yet clear whether these PBAN-like peptides are involved in control of the pheromone gland. Nevertheless, our findings suggest that in H. virescens , optimal production of sex pheromone depends on both neural and hormonal regulation.