Female Helicoverpa armigera sex pheromone production is under the control of pheromone biosynthesis-activating neuropeptide (PBAN). After mating, females undergo suppression of sex pheromone production and enhanced oviposition as a result of the transfer of male-derived seminal peptides. In a previous study we identified a putative H. armigera sex-peptide receptor (HeaSP-R) and demonstrated a significant up-regulation in gene expression levels of this receptor in brains and pheromone glands of mated females, thereby implicating a regulatory role for sex peptide in the reproductive behaviour of H. armigera. In the present study, we show that virgin females injected with Drosophila melanogaster SP (DrmSP), in addition to inhibition of pheromone production, also exhibited a suppression of calling behaviour and a significant reduction in the gene expression levels of the PBAN-receptor. In addition, RNA interference (RNAi) silencing of the HeaSP-R expression by 50-60% prevented DrmSP-suppression of pheromone production and calling behaviour. Moreover, mated, silenced females failed to increase their oviposition rates as is normally observed in mated females, and their behaviour did not differ from that of virgin females. However, sex pheromone production by mated, silenced females remained low, comparable to mated, normal females, thereby indicating the probable involvement of additional factors in the suppression of sex pheromone production after mating.

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Insect males produce accessory gland (MAG) factors that are transferred in the seminal fluid to females during copulation, and elicit changes in the mated female's behavior and physiology. Our previous studies showed that the injection of synthetic Drosophila melanogaster sex-peptide (DrmSP) into virgin females of the moth Helicoverpa armigera causes a significant inhibition of pheromone production. In this and other moth species, pheromone production, correlated with female receptivity, is under neuroendocrine control due to the circadian release of the neuropeptide PBAN. In this study, we show that PBAN, present in the hemolymph during the scotophase in females, is drastically reduced after mating. We also identify 4 DrmSP-like HPLC peaks (Peaks A, S1, S2, and B) in MAGs, with increasing levels of DrmSP immunoreactivity during the scotophase, when compared to their levels observed during the photophase. In H. armigera MAGs, a significant reduction in the pheromonostatic peak (Peak B) was already evident after 15 min of copulation, and depletion of an additional peak (Peak S2) was evident after complete mating. Peak A is also detected in female brains, increasing significantly 1 h after mating, at which time inhibition of pheromone biosynthesis also occurs. However, changes corresponding to the other MAG peaks were not detected in mated female tissues.

Abstracti mb_937 77..86Sex pheromone production in Helicoverpa armigera is regulated by pheromone-biosynthesis-activating neuropeptide (PBAN), which binds to a G-protein coupled receptor at the pheromone gland. We demonstrate the temporal differential expression levels of the PBAN receptor (PBAN-R) gene, reaching peak levels at a critical period of 5 h post-eclosion. Previous studies implied a possible regulatory role for juvenile hormone (JH). We herein demonstrate that PBAN-R expression levels increase normally when females are decapitated or head-ligated, removing the source of JH, before peak transcript levels are reached. Similarly, sex pheromone production can be induced by PBAN in such decapitated females. These results indicate that up-regulation, at this critical time, is not dependent on JH originating from the head. Conversely, JH injected in vivo at this critical period significantly inhibits PBAN-R transcript levels.