Paraconfusus pheromone components

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. 

Figure 6.11 Biosyntheses of isoprenoid pheromone components by bark and ambrosia beetles from host conifer monoterpenes. (A) Conversion by the male California fivespined ips, Ips paraconfusus Lanier (Coleoptera Scolytidae), of myrcene from the xylem and phloem oleoresin of ponderosa pine, Pinus ponderosa Laws., to (4S)-(+)-ipsdienol and (4S)-(-)-ipsenol, components of the aggregation pheromone (Hendry et al., 1980). (B) Conversion by male and female I. paraconfusus of (1 S,5S)-(-)-a-pinene (2,6,6-trimethyl-bicyclo[3.1,1]hept-2-ene) from the xylem and phloem oleoresin of P. ponderosa to (1 S,2S,5S)-(+)-c/s-verbenol (c/s-4,6,6-trimethyl-bicyclo[3.1,1]hept-3-en-2-ol), an aggregation pheromone synergist and of (1 R,5R)-(+)-a-pinene to (1 fl,2S,5fl)-(+)-frans-verbenol (frans-4,6,6-trimethyl-bicyclo[3.1,1]hept-3-en-2-ol), a compound of unknown behavioral activity for /. paraconfusus. Male and female western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera Scolytidae), convert (1 S,5S)-(-)-a-pinene to (1S,2ft,5S)-(-)-frans-verbenol, an aggregation pheromone interruptant and (1R,5R)-(+)-a-pinene to (1 R,2S,5R)-(+)-frans-verbenol, a compound of...

Figure 6.16 Model illustrating interspecific regulatory differences in an early-stage reaction in isoprenoid pheromone biosynthesis between male Ips paraconfusus Lanier and Ips pini (Say). Feeding on host phloem results in synthesis of the full amount of the major pheromone component and full activity of HMG-R for both species. The impact of feeding on HMG-R transcript levels is yet to be determined. Topical treatment of male I. pini with JH III mimics feeding nearly completely in terms of pheromone mass and HMG-R activity. Topical treatment of male I. paraconfusus with JH III does not mimic feeding in terms of pheromone mass or HMG-R activity. Topical treatment of both species with JH III results in significantly enhanced levels of HMG-R transcript. One hypothetical explanation for the interspecific difference is that a second hormone (SH) or factor may be associated with the synthesis, stability, and/or activity of HMG-R in I. paraconfusus.

A similar phenomenon was reported by us in 1976.50 (13 ,43 ,53 )-dx-Verbenol (Figure 4.25) is a pheromone component of the bark beetle, Ips paraconfusus. At that time there was a confusion concerning the name of that pheromone component. Some people called (15 ,45 ,55 )-cw-verbenol as (+)-dx-verbenol, while others called it (-)-ds-verbenol. Our study of this compound revealed it to be levorotatory in chloroform, while dextrorotatory in methanol and acetone. 

QUILICI, D.R., De novo biosynthesis of aggregation pheromone components by the pine bark beetles, Ips paraconfusus (Lanier) and Ips pini (Say) (Coleoptera Scolytidae), and identification of an interruptant and a synergist produced by Ips pini., Ph.D., 1997, University of Nevada, Reno. 

Male I. paraconfusus have a greater overall antennal sensitivity to ( - )ipsdie-nol produced by I. pini than to their pheromonal component (+)ipsdienol (Light and Birch, 1982). Females, however, show a greater and more typical response to their pheromonal enantiomer. 

This distinction clarifies the surprising differential sensitivity of male and female 7. paraconfusus to components of their pheromone and to that of I. pint. Males and females are equally sensitive to their natural pheromone and to its component, (+ )ipsdienol, over a wide range of concentrations. However, females are significantly more sensitive to pheromonal ( + )ipsdienol than to allomonal (-)ipsdienol (the pheromone of I. pini), whereas males are more sensitive to allomonal (- )ipsdienol than to their own pheromonal (+ )ipsdienol (Light and Birch, 1982). There is a clear adaptive advantage for males to locate new host material quickly and to avoid resources occupied by /. pini, unless nothing else is available, since if the two species do co-colonize a resource, the reproductive potentials of both are reduced. This premium on selection of unoccupied resources underlies the high sensitivity of males to allomonal ipsdienol. The interruption of response in 7. paraconfusus by verbenone from D. brevicomis may have a similar basis. 

The small proportion of (- )ipsdienol in the pheromone blend of 7. paraconfusus might similarly be advantageous in spite of it being the pheromone of its competitor, 7. pini, because (- )ipsdienol also appears to deter 7. latidens. The exploitation of pheromone components by predators need not necessarily select for different attractive blends but could result in selection for components that interrupt the predator response. For example, the highly specific response of T. chlorodia to exo-brevicomin from female D. brevicomis is interrupted by... 

As with the previous discussions of the selective forces that mold the communication channel, it is difficult to arrive at either definitive proofs or absolute refutations of these models. Notwithstanding such difficulties, several cases provide illuminating evidence of the potential contribution of sex pheromones to the speciation process. In many of the bark beetles it is known that the aggregation pheromone is biosynthesized from precursors obtained by the feeding adult beetles from the phloem of the host trees. In Ips paraconfusus the pheromone component cw-verbenol is biosynthesized from the host terpene (-)-pinene. Ingestion of the opposite isomer produces the opposite optical form of the pheromone (Renwick et al., 1976). Clearly this suggests that beetles... 

Addition of an allylsilane to acid chlorides has been used to synthesize ipsenol and ipsdienol, principal components of the aggregation pheromone of the bark beetle Ips paraconfusus (Figure Si6.3). It is of note that the allylsilane used in these syntheses is a versatile source of the isoprene unit. 

Ipsenol (111, Figure 4.63), ipsdienol (112) and cw-verbenol (A) were isolated and identified in 1966 by Silverstein et al. as the components of the male-produced aggregation pheromone of a bark beetle, California five-spined ips (Ips paraconfusus). 

Figure 4.63 Components of the aggregation pheromone of Ips paraconfusus. Modified by permission ofShokabo Publishing Co., Ltd...

That microorganisms in the gut of an insect are capable of converting substances from food plants into chemicals which can be used as pheromones has been demonstrated by several authors. Thus while Pearce et al. 171) reported that a// Aa-cubebene (11) one of the components in the aggregation pheromone released by Scolytus multistriatus, is produced by the host. Brand et al 172) found that a bacterium isolated from the gut of Ips paraconfusus converts alpha-pintnQ (12) to cis- and trans-wQvhQnol (13, 14) and myrtenol (15). 

The aggregation pheromone of I. paraconfusus consists of a mixture of three components cw-verbenone (16), ipsenol (21) and ips-dienol (22). Although the (S)-( —)-isomer of ipsenol acts as an attrac-tant to /. paraconfusus, the (i )-(-h) isomer acts as an inhibitor 469),... 

Fig. 12.1 Aggregation pheromones of (a) Ips paraconfusus, three male-produced synergistic components - (+ )2-methyl-6-methylene-2,7-octadien-4-ol (ipsdienol) (-)2-methyl-6-methylene-7-octen-4-ol (ipsenol) and cw-verbenol. (b) Dendroctonus brevicomisj three attractive components, cxo-7-ethyl-5-methyl-6,8-dioxabicyclo-[3.2.1] octane (cxo-brevicomin) from the female l,5-dimethyl-6,8-dioxabicyclo-[3.2.1] octane (frontalin) from the male and myrcene released from the host tree. Verbenone and trans-verbenol, released after a male locates the female, interrupts response to the attractant blend.

Fig. 12.3 Biosynthesis of the components of the aggregation pheromone of Ips paraconfusus by simple conversion from the host tree terpenes myrcene and a-pinene.

The production of ipsdienol and ipsenol in I. paraconfusus appears to be under hormonal control (Hughes and Renwick, 1977 Borden et al., 1969). Pheromone production, normally stimulated by feeding, could also be induced by treatment with juvenile hormone. In /. cembrae, which attacks living larch trees, ipsdienol and ipsenol are produced on contact with myrcene vapour, without feeding, but production of a third component (3-methyl-3-buten-l-ol) appears to be controlled hormonally (Renwick and Dickens, 1979). The extent of hormonal stimulation of pheromone release is, however, still equivocal. 

Specificity of communication between 7. paraconfusus and 7. pini is based not only on the non-attraction that would be expected from species of different groups, but also on mutual interruption of the other s response (Birch and Wood, 1975). Two components of the male pheromone of 7. paraconfusus, (- )ipsenol and (+)ipsdienol, completely interrupt the response of 7. pini to its own pheromone (Birch eta/., 1977 Birch etal., 1980a). Similarly, (- )ipsdienol, the pheromone of 7. pini, interrupts the response of 7. paraconfusus to its... 

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