Abstract
Bark beetles use aggregation pheromones to coordinate host colonization and mating. These monoterpenoid chemical signals are produced de novo in midgut cells via the mevalonate pathway, and pheromone production is induced when an adult beetle feeds on phloem of a host tree. In Ips pini, juvenile hormone (JH) III influences key regulatory enzymes along the mevalonate pathway that leads to pheromone production. In fact, topically applied JH III is sufficient to stimulate pheromone production in unfed males. In this study, we explore the influence of feeding and JH III treatment on pheromone production in male Ips confusus, the pinyon Ips. We also characterize the influence of feeding and JH III treatment on transcript levels and activity of three key enzymes involved in pheromone biosynthesis: 3-hydroxy-3-methylglutaryl-CoA (HMG) synthase (HMGS), HMG-CoA reductase (HMGR) and geranyl diphosphate synthase (GPPS). We also extend the current understanding of the regulation of pheromone biosynthesis in I. pini, by measuring the influence of feeding and JHIII treatment on enzymatic activity of HMGS and GPPS. Feeding on host phloem alone strongly induces pheromone production in male I. confusus, while JH III treatment has no effect. However, feeding and JH III both significantly up-regulate mRNA levels of key mevalonate pathway genes. Feeding up-regulates these genes to a maximum at 32 h, whereas with JH III-treatment, they are up-regulated at 4, 8, and 16 h, but return near to non-treatment levels at 32 h. Feeding, but not JH III treatment, also increases the activity of all three enzymes in I. confusus, while both feeding or treatment with JH III increase HMGS and GPPS activity in I. pini. Our data suggest that pheromone production in Ips is not uniformly controlled by JH III and feeding may stimulate the release of some other regulatory factor, perhaps a brain hormone, required for pheromone production.
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Acknowledgements
We thank the Bureau of Land Management Carson City District Office and the US Forest Service, South Tahoe District for permission to collect harvest beetle infested trees; Marilyn Kunzli-Howell and Joni Nastal for assistance with the HMGR enzyme assays; and Anna Gilg assistance with the GPPS enzyme assay for providing partial sequences of IcHMGR and IcGPPS. This work was funded by a USDA-NRI grant no. 2004-35607-14878 awarded to MDG, a NSF-EPSCoR grant awarded to AGH and the Nevada Agriculture Experiment Station, and is a contribution of the Nevada Agriculture Experiment Station, publication no. 03087109.
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Bearfield, J.C., Henry, A.G., Tittiger, C. et al. Two Regulatory Mechanisms of Monoterpenoid Pheromone Production in Ips spp. Of Bark Beetles. J Chem Ecol 35, 689–697 (2009). https://doi.org/10.1007/s10886-009-9652-2
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DOI: https://doi.org/10.1007/s10886-009-9652-2