Regulation of pheromone production in the gypsy moth, Lymantria dispar, and development of an in vivo bioassay

Abstract

Production of sex pheromone in females of the gypsy moth, Lymantria dispar, is regulated primarily by a pheromonotropic factor originating in the head. Decapitation of a female caused depletion of pheromone in the pheromone gland; however, in contrast with several other species of moths, biosynthesis could not be reinitiated by injection of brain-suboesophageal ganglion homogenates or synthetic pheromone biosynthesis activating neuropeptide (PBAN). Severing the ventral nerve cord (VNC) in the abdominal region of females cuased termination of pheromone production. While PBAN was inactive in decapitated females, if the VNC was also transected, PBAN injection resulted in significant pheromone production. Moreover, delivery of PBAN directly to the posterior cut-end of VNC, injection of PBAN into the terminal abdominal ganglion (TAG), or electrical stimulation of TAG, resulted in significant pheromone production. Together, these results suggest that in this species, the pheromonotropic factor travelling via the VNC is an important regulator of pheromone production. However, the pheromonotropic response was very high only if VNC posterior to the thoracic ganglia was severed before injection of PBAN into the TAG or electrical stimulation of TAG. The latter result indicates that an inhibitory factor may be present in the thoracic ganglia. Administration of pheromonotropic factors to the posterior cut-end of VNC can be used as a bioassay for the gypsy moth and possibly for other species in which these factors are transported via the VNC.