Isolated abdomen and pheromone gland bioassays were utilized to determine the physiological action of the pheromone-biosynthesis-activating neuropeptide (PBAN) in the corn earworm moth Helicoverpa (= Heliothis) zea. An isolated pheromone gland bioassay showed that synthetic PBAN was active at 0.02 pmol, with maximal activity occurring at 0.5 pmol and 60 min of incubation. Second-messenger studies demonstrated that extracellular Ca2+ is necessary for PBAN activity on isolated pheromone glands. The Ca2+ ionophore A23187 stimulated pheromone biosynthesis alone, whereas the Ca2+ channel blockers La3' and Mn2+ inhibited PBAN activity. However, the organic Ca2+ channel blockers verapamil and nifedipine did not inhibit PBAN activity. Both forskolin and two cAMP analogues stimulated pheromone biosynthesis in the absence of extracellular Ca2+, indicating that Ca2+ may activate an adenylate cyclase. The biogenic amine octopamine did not elicit pheromone production in isolated gland or abdomen bioassays or when in ected into intact female moths. Removal of the ventral nerve chord, including the terminal abdominal ganglia in isolated abdomens, did not affect PBAN stimulation of pheromone production. Similar levels of stimulation were found when isolated abdomens were treated with PBAN in scotophase or photophase.Sex pheromone titers in most moths, including the corn earworm moth Helicoverpa (= Heliothis) zea, fluctuate diurnally with little or no pheromone present during the day and with peak pheromone titers occurring during midscotophase (1). This fluctuation is caused by the release and/or degradation of existing pheromone and the biosynthesis of new pheromone at precise times of the photoperiod. The biosynthesis of pheromone in H. zea is regulated by a peptide produced in the subesophageal ganglion (SEG) portion of the brain complex of female moths (2). This peptide, termed pheromone-biosynthesis-activating neuropeptide (PBAN), has been isolated and sequenced from brains of H. zea (3).Two other pheromonotropic peptides, each with about 80%o sequence identity with H. zea PBAN, have been isolated from the brains of the silkworm, Bombyx mori (4, 5). These peptides have been synthesized and the synthetic peptides retain biological activity, with cross-reactivity occurring in other species of moths (3, 4, 6, 7). These reports and others indicate that a variety of moths utilize PBAN or PBAN-like peptides in controlling pheromone biosynthesis.Although PBAN or PBAN-like activity has been identified in several different moth species, the physiological mode of action of PBAN has not been determined conclusively for any one species. In fact, there are two apparently conflicting hypotheses on how PBAN activates pheromone biosynthesis, and both are based on studies utilizing Heliothis moths as experimental animals. One hypothesis suggests that PBAN is synthesized in the SEG, transported to the corpora cardiaca, and then released into the hemolymph, where it can act on the pheromone gland to induce pheromone biosynthesis (8)....

Hormonal control of the production of the main sex pheromone component, Z11-hexadecenal (Z11-16:Ald), of female Helicoverpa zea was investigated using labeled precursors to monitor the pheromone biosynthetic pathway. The pathway originates with the biosynthesis of palmitic acid followed by A11 desaturation to form the intermediate Z11-16:Acid, which is then reduced to a primary alcohol and then oxidized to Z11-16:Ald. Incubation of glands either in vivo or in an isolated gland culture with the deuterium labeled compounds, D3-16:Acid or D9-Z11-16:Acid, yielded no differences in label incorporation into pheromone in the presence or absence of synthetic PBAN (Pheromone biosynthesis activity neuropeptide). However, unlabeled pheromone titers increased about tenfold above controls in the presence of PBAN in both in vivo and in vitro cultures. When isolated glands were incubated with [1-'4Clacetate, about a thirtyfold increase in the incorporation of radiolabel into Z11-16:Ald above controls was observed in the presence of PBAN. Also, about a tenfold increase in incorporation was observed in saturated and monounsaturated fatty acids found in the gland upon stimulation with PBAN. These results indicate that the hormone PBAN controls pheromone biosynthesis in H. zea by regulating a step in or prior to fatty acid biosynthesis.

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