Jeffreyi pheromone components

Evidence for de novo synthesis of pheromone components was obtained by showing that labeled acetate and mevalonate were incorporated into ipsdienol by male Ips pini [103,104]. Similarly, labeled acetate and other labeled intermediates were shown to be incorporated into frontalin in a number of Dendroctonus species [105]. Possible precursors to frontalin include 6-methyl-6-hep-ten-2-one, which was incorporated into frontalin by D. ruffipennis [106]. The precursor 6-methyl-6-hepten-2-one also was shown to be converted to bre-vicomin in the bark beetle, Dendroctonus ponderosae [107]. In addition, the expression patterns of HMG-CoA reductase and HMG-CoA synthase are tightly correlated with frontalin production in Dendroctonus jeffreyi [108, 109]. A geranyl diphosphate synthase cDNA from I. pini was also isolated, functionally expressed, and modeled [110]. These data indicate that the de novo isoprenoid biosynthetic pathway is present in bark beetles. A variety of other monoterpene alcohols such as myrcenol, pityol, and sulcitol are probably synthesized through similar pathways [111]... 

Hall G. M., Tittiger C., Blomquist G. J., Andrews G., Mastick G., Barkawi L. A., Bengoa C. S. and Seybold S. J. (2002b) Male Jeffrey Pine Beetles, Dendroctonus jeffreyi, synthesize the pheromone component frontalin in anterior midgut tissue. Insect Biochem. Mol. Biol. 32, 1525-1532. 

Specialization of midgut cells for synthesis of male isoprenoid pheromone components in two scolytid beetles, Dendroctonus jeffreyi and Ips pini. Tissue Cell. (in press). 

Nardi J. B., Young A. G., Ujhelyi E., Tittiger C., Lehane M. J. and Blomquist G. J. (2002) Specialization of midgut cells for synthesis of male isoprenoid pheromone components in two scolytid beetles, Dendroctonus jeffreyi and Ips pini. Tissue and Cell 34,221-231. 

Figure 7.5 Tissue localization of HMG-R expression. Exposed whole mounts show that HMG-R mRNA is observed in the midgut of JH Ill-treated male D. jeffreyi (A) and I. pini (C), but not in untreated insects (B, D). Panels E through H show whole mount hybridizations of isolated I. pini alimentary canals. HMG-R expression in the anterior midgut (AMG, marked by brackets) correlates with pheromone production in starved, JH Ill-treated males (E) and fed males (G), while starved and untreated males (F, G), which do not produce monoterpenoid pheromone components, do not strongly express HMG-R. Asterisks mark non-specific signal in the hindguts. PV, pro-ventriculus HG, hindgut. Scale bars = 0.5 mm. Figure modified from Hall et al. (2002a, 2002b) with permission.

Evidence accumulated for and against the paradigm that bark beetle pheromone biosynthesis involved direct modification of host precursor monoterpenes. For 1. pini, the issue was laid to rest with the demonstration that male tissues incorporate radio-labeled acetate into ipsdienol in a manner consistent with pheromone production. Similar experiments proved the de novo biosynthesis of frontalin, an important isoprenoid-derived semiochemical produced by male Dendroctonus jeffreyi It is probable that other Coleoptera can also synthesize monoterpenes, either as pheromone components " or defensive compounds. Despite the capacity for de novo biosynthesis, plant precursor modification is likely an important source of pheromone components for some species. In these cases, plant chemicals could enter the pheromone biosynthetic pathway at later steps. 

HALL, G.M., TITTIGER, C., BLOMQUIST, G.J., ANDREWS, G.L., MASTICK, G.S., BARKAWI, L.S., BENGOA, C., SEYBOLD, S.J., Male Jeffrey pine beetle, Dendroctonus jeffreyi, synthesizes the pheromone component frontalin in anterior midgut tissue,/wsecr /oc/ er . Molec. Biol, 2002, 32, 1525-1532. 

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