Frontalin biosynthesis

Jeffrey pine beetle, Dendroctonus jeffreyi Hopkins, which had been previously treated with juvenile hormone III (JH III, 2.2 pg/beetle in acetone) and then placed in an aeration tube for 25 to 30 h. Ips paraconfusus and I. pini were each injected with 0.2 pCi of sodium [1-14C]acetate prior to placement in cut pine logs and volatile collection, while D. jeffreyi were each injected with 3.8 (male) and 3.7 (female) pCi of sodium [1-14C]acetate 6.4 (male) and 10.7 (female) h after JH application. (G) The role of the mevalonate pathway in frontalin biosynthesis is supported by the incorporation of radiolabel from [2-14C]mevalonolactone into frontalin by male D. jeffreyi (2.2 pg JH 11 l/beetle in acetone, 10 h incubation and volatile collection, 1.1 pCi of [2 14C] mevalonolactone injected, 20 h volatile collection). Figures adapted from Seybold et al. (1995b) and Barkawi (2002). 

Figure 6.13 Examples of the application of normal-phase, radio-HPLC to the analysis of de novo biosynthetic pathways in bark beetles (Scolytidae). Demonstration of sex-specific de novo biosynthesis of ipsenol, ipsdienol, and amitinol through radio-HPLC analysis of pentane extracts of Porapak-trapped volatiles from (A) male and (B) female Ips paraconfusus Lanier feeding for 168 h in Pinus ponderosa and (C) male and (D) female Ips pini (Say) feeding for 168 h in Pinus jeffreyi (Seybold et al., 1995b). Demonstration of sex-specific de novo biosynthesis of frontalin through radio-HPLC analysis of pentane extracts of Porapak-trapped volatiles from (E) male and (F) female...

Barkawi L. S., Francke W., Blomquist G. J. and Seybold S. J. (2003) Frontalin de novo biosynthesis of an aggregation pheromone component by Dendroctonus spp. bark beetles (Coleoptera Scolytidae). Insect Biochem. Mol. Biol. 33, 773-788. 

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. 

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