Pheromone interruption

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...

Crustaceans are known to use pheromones in behavioral contexts other than avoidance, including reproduction and social interactions. For example, at least one spiny lobster, the California spiny lobster Panulirus interrupts, has been shown to be attracted to the odor of conspecifics.131 This pheromonal phenomenon is taken advantage of by workers in the lobster fishery, who use live lobsters as bait in their pots.132 However, relatively little research has been performed on the topic of aggregation pheromones, including the nature of the signal and its sensory reception. Pheromonal chemical signals are also involved in the establishment and maintenance of social hierarchies in crustaceans.133 134... 

The compound XIV occurs widely as a component of lepidopt-erous sex pheromones, especially of pests of stored grain and dried fruit (2). The synthesis discussed below is an example of the preparation of a "skipped" or "methylene-interrupted" 1,4-diene. It is important to have pure XIV for pheromone studies since the other stereoisomers can act as inhibitors of the behavioral response in some species. 

More chemical specificity is represented by the structure of the sex pheromone released by females of the Korean population of the apple leaf miner Lyonetia prunifoliella. The main compound is 10,14-dimethyl-l-octadecene (M25), which is accompanied by minor amounts of the saturated hydrocarbons, 5,9-dimethyloctade-cane and 5,9-dimethylheptadecane 902 Earlier, the three compounds were reported to be components of the sex pheromone for the North American population of the moth.903 During bioassays in Korea, all (S, -configured isomers proved to be electrophysiologically active, whereas (105,145)-dimethyloctadec-l-ene elicited the strongest response. In contrast to the North American insects, (105,145)-M25 was found to attract the moths as a single compound. In the case of the Lyonetia compounds, the structure M25 suggests the incorporation of two propanoate units interrupted by an acetate unit. 

Arrangements involving the formation of two (or more) methyl groups and formal interruptions by acetate will typically result in an uneven number of methylene groups between the methyl branchings — just as it is shown by most of the branched-chain insect pheromones. 

We observed that when adult females of the corn earworm moth (Heliothis zea) were ligated between the head and thorax so that normal hemolymph circulation between the brain and the rest of the body was interrupted, they did not produce sex pheromone. However, the ligated females could be stimulated to produce pheromone, in amounts not different from that produced by normal females, by an injection of a saline extract of the female brain. Our studies with this nocturnal moth indicate that the neurohormone is stored in the brain and released into the hemolymph in the scotophase causing timely production of pheromone by the female. 

Because synthetic ( )-87 was pheromonally inactive, Tumlinson et al. carefully studied in 1977 the relationship between the enantiomeric purity of 87 and its pheromone activity.60 They synthesized the enantiomers of 87, starting from the enantiomers of glutamic acid. The bioactive enantiomer is (/ )-(—)-87, and (5 )-(+)-87 severely inhibits the action of (R)-87. Accordingly, (R)-87 of 99% ee is only two-thirds as active as pure (R)-S7 that of 90% ee is one-third as active, that of 80% ee is one-fifth as active as pure (R)-87. Both (7v )-87 of 60% ee and ( )-87 were inactive. These results illustrate convincingly the importance of enantiomeric composition in chemical communication. Later in 1996, Leal found that the sex pheromone of the female scarab beetle (Anomala osakana) is (S )-87, while (R)-87 interrupts the attraction caused by (.S )-87,61 Thus, chirality accounts for species discrimination. 

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. 

Nine stimuli were used. These were 3 non-familiar stimuli (amyl acetate, B-ionone, 2-phenylethanol 10 M), various relevant natural stimuli, such as 4 amino acids (L-Ala, L-Glu, L-Arg, L-Lys 10 - 10 M), a bile acid (taurolithocholic acid, I0 - 10" M), and a preovulatory pheromone (17a,20B-dihydroxy-4-pregnen-3-one, 10" - 10 M). The compounds were dissolved in tap water and for 15s repetitively applied to the olfactory epithelium. The 15s stimulus applications were interrupted by 180s tap water application of similar (1 ml/min) velocity during the interstimulus phases. 

Comparison of the pheromone systems of closely related species, has revealed that the attraction and the pheromone-receptor interaction found between them correlates with the degree of relatedness (Lanier and Wood, 1975 Priesner, 1979a, b). However, such a cross attraction could be disadvantageous for related species living in the same area, and under such circumstances an additional interspecific mechanism - interruption - is found which serves to maintain the isolation between sympatric species (Birch, Chapter 12). Thus, one species may produce an additional pheromone compound which interrupts the attraction of the other species. Chemical compounds which function as pheromones may also serve as cues for predators, parasitoids and prey (Vincent, Chapter 8). In these cases the predator or parasites have developed capabilities for recognizing the pheromones of their prey or host insects. Predators may also produce the attractants of their prey (Weaver, 1978 Eberhard, 1977). Conversely, some insect species have developed defensive compounds which are avoided by both insect and vertebrate predators, (cf. Eisner, 1970 Blum, 1978 Huheey, Chapter 10). Finally, during... 

Most compounds which interfere with a behavioral response elicited by another compound are interspecific interruptants and are also pheromone components of sympatric species (see Birch, Chapter 12 Card6 and Baker, Chapter 13). They interrupt the attraction of closely related sympatric species, which may otherwise be cross-attracted by other pheromone components or host volatiles. In some instances the interruption is mutual, (Light and Birch, 1979 Lanier et al., 1980 Birch et al., 1980a, b), and it might well be that this is a general phenomenon. 

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.

The sensitivity of pheromone perception in bark beetles appears to be generally typical of the very high sensitivity shown by many insects to their pheromones (Seabrook, 1978 Payne, 1979 see also Mustaparta, Chapter 2). In general, beetles have a lower threshold for their own pheromonal components than to other terpenes and related compounds (Mustaparta et al., 1979 Dickens, 1981). In I. pini, receptor cells specialized for pheromone perception respond minimally, if at all, to host compounds, and vice versa (Mustaparta et al., 1979,1980). However, the behavioral interruption of the response of I. pini to (- )ipsdienol by a few percent of (+ )ipsdienol or by ipsenol must be due to processing in the central nervous system of the insect and not to any interaction of compounds at the antennal receptor sites. Similarly, the synergistic effect of a pheromone blend is due to central integration. 

Where several species of bark beetle co-exist and also use the same host tree species for breeding, one species may exploit the pheromone of another and so colonize a host more efficiently, or conversely, it may avoid the pheromone of another species and so avoid potential hybridization or detrimental competition for a resource. Wood (1970) suggested that the specificity of pheromones in the Scolytidae might be one mechanism maintaining breeding isolation between sympatric species. This has been substantiated for sympatric species of Ips, and besides breeding isolation, competition for host resources is also mediated via chemical communication. Two mechanisms have been discovered (i) nonattraction to the pheromone of another species, and (ii) interruption of a potential response to host material occupied by another species. 

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... 

Table 12.2 Mutual interruption of response to their aggregation pheromones by Ips paraconfusus and I. pini. Treatments are male beetles of one or both species boring in ponderosa pine, with, in some treatments, one or more enantiomers or racemic ipsenol and ipsdienol. Responses are given as a percentage of the response to conspecifics. (Data from Birch and Wood, 1975 Light and Birch, 1979 Birch et al., 1980a)...

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