Pheromone bark beetle aggregation

Terpenes are known to play important ecological roles not only in the defense of the tree, but also in bark beetle chemical ecology. Two chapters in this volume (see chapters by Raffa, et al, and Tittiger, et al.) review aspects of terpenoids as chemicals in conifer-bark beetle interactions and isoprenoid formation in bark beetle chemical ecology. While some species of bark beetles may be able to produce monoterpene pheromones de novo, bark beetles can also use host-derived monoterpenes as precursors to their own sex and aggregation pheromones. Bark beetle monoterpene pheromones are often used in a stereospecific manner such that often only one enantiomer is able to serve as a sex or aggregation pheromone. Since both enantiomeric host-derived monoterpene precursors are accepted and chemically modified by the beetle, the exact monoterpene enantiomeric mixture of conifer resin is important to both the beetle s ability to produce the correct pheromone and to the trees ability to escape an attack. ... 

This chapter has described what has been learned about bark beetle aggregation behavior in the 15 years since the first pheromone was identified from /. paraconfusus. It has also indicated how little we yet know about many of the behavioral aspects of aggregation. Our ability to make highly resolved enantiomers of pheromones opens the way to analyse these behaviors more precisely. Similarly, the biosynthesis of pheromones from host compounds, the orientation mechanisms used by beetles in flight, the pheromone production of individual beetles, and their interaction with sonic and visual stimuli can now all be used to understand the many behavioral steps taken by individual beetles from eclosion to mating and egg laying, which will result in a composite picture of tree colonization built up from information rather than intuitive assumptions. 

Claisen rearrangement of glycolates. Two laboratories 2 have reported that allylic glycolate esters undergo Claisen-Ireland rearrangement (6, 276-277) with useful diastereoselectivity. This rearrangement was used in a synthesis of 1, the aggregation pheromone of the European elm bark beetle.1... 

The male produced aggregation pheromone of the beech bark beetle, Taphrorychus bicolor is (lS,2T,5E)-bicolorin 261 [482,483]. Its carbon skeleton may represent a rearranged terpene. 

Separation of terpinen-4-ol enantiomers performed by a chiral GC columnand a chiral lanthanide shift reagent Eu(hfc)3, showed that the enantiomeric composition of an isolated compound from sweet marjoram oil was 73% (5)(- -) 27% R) —). The (4f )(—)-enantiomer was found in the oil of Eucalyptus dives Terpinen-4-ol was also found in several bark beetle species and is the main component in the aggregation pheromone of Polygraphuspoligraphus ... 

Attempts to investigate boll weevil (Anthonomus grandis) pheromone biosynthesis have identified isomerization, dehydration, and oxidation of the pheromone alcohols, and anticipated allylic oxidation of myrcene and limonene, but no evidence for the cyclization of acyclic precursors. The aggregation pheromones of bark beetles have been reviewed. Ips calligraphus responds to ipsdienol only in the presence of the c/5-verbenol (32) large additional concentrations of the enantiomer (l/ ,4i ,5/ )-(32) reduce beetle response. 5-(-)-Ipsenol, the pheromone of Ips grandicollis, increases the response of /. avulsus to its own pheromone ipsdienol. ... 

The aggregation pheromones of insects can be classified into two groups those emitted by males or females to attract both sexes simultaneously for resource exploitation and/or mating (e.g., bark beetles Byers, 1989) and those emitted to attract and arrest individuals of specific developmental stages, as found in the German cockroach Blattella germanica (Ishii and Kuwahara, 1967,1968 Sakuma and Fukami, 1990, 1993). 

As is indicated in Fig. 22-3, the same intermediate cation can yield a variety of end products. For example, pure geranyl diphosphate pinene cyclase catalyzes formation of several other terpenes in addition to a-pinene.89 Another aspect of terpene synthesis is that insects may convert a plant terpene into new compounds for their own use. For example, myrcene, which is present in pine trees, is converted by bark beetles to ipsenol (Fig. 22-3), a compound that acts as an aggregation pheromone.90... 

Cycloaddition to a cyclic allyl ether The key step in a synthesis of lineatin (3), the aggregation pheromone of the bark beetle, is the addition of dichloroketene to the alkene 1. Under usual conditions (POCl3, 8,156) the desired adduct is obtained in 7% yield. Fortunately, substitution of 1,2-dimethoxyethane for POCl3 increases the yield of 2 to 50-60%. 

Stereoselective reactions with aldehydes. The related (E)-2-pentenyltin reagent 2 also reacts with aldehydes to form predominantly erythro adducts such as 3. This reaction was used for a stereoselective synthesis of an aggregation pheromone (4) of the European elm bark beetle.1... 

The trap-out treatment generally utilizes the aggregation pheromone of the target bark beetle species in association with a trap that kills the adults, i.e. sticky traps or containers that prevent the escape of species coming in contact with them. These techniques are not species specific per se because of the attraction of the natural enemies to the aggregation pheromones, i.e. kairomonal activity. Hence, the natural enemies are also trapped resulting in mortality to the adults. 

Seybold S. J., Quilici D. R., Tillman J. A., Vanderwel D., Wood D. L. and Blomquist G. J. (1995) De novo biosynthesis of the aggregation pheromone components ipsenol and ipsdienol by the pine bark beetles Ips paraconfusus Lanier and Ipspini (Say) (Coleoptera Scolytidae). Proc. Natl. Acad. Sci. USA 92, 8393-8397. 

Barkawi L. S. (2002) Biochemical and molecular studies of aggregation pheromones of bark beetles in the genus Dendroctonus (Coleoptera Scolytidae), with special reference to the Jeffrey pine beetle, Dendroctonus jeffreyi Hopkins. PhD thesis. Univ. Nevada, Reno, 193 pp. 

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