Plant-derived pheromone

A question that was posed early on in determining biosynthetic pathways of the pheromones was the origin of the precursors. There was some indication that plant derived compounds could be ingested and modified by the insect into a pheromone. We now know that in some cases this occurs [7], but for the most part pheromones are biosynthesized de novo by the insect [8]. For most of the pheromones studied to date it is apparent that biosynthetic pathways of normal metabolism have been altered to produce specific pheromone components. Several enzymes in these biosynthetic pathways have been modified to produce species specific pheromone components. 

In the next chapter we will look at the ways in which the ideas and principles we have talked about in this chapter, and the reactions you have met in the 23 preceding ones, can be used in a practical way to make useful and interesting molecules. We will look at the synthesis of some of the molecules found in nature, such as hormones, plant-derived products with medicinal properties, and insect pheromones, as well as others that Nature has not made but that for one reason or another man has chosen to make. 

Tony Hooper (Rothamsted Research, UK) discussed local applications of push-pull insect-control strategies with plant-derived semiochemicals and pheromones in the control of crop pests. For example a sudan grass trap crop reduced the number of stem borers on maize grown in adjacent plots. Five thousand African farmers have already been involved in a practical test of the methodology which exploits plant diversity in a very creative way. It was an excellent example of an understanding of chemistry and biotechnology being put to practical use in a local context. 

Aphid Alarm Pheromone. The alarm pheromone of aphids in the subfamily Aphidinae is ( )-P-famesene. The pheromone can be synthesized easily, but it is unstable under field conditions and therefore has limited potential for application. Although many plants produce this volatile chemical constitutively in their essential oil, aphids can differentiate between plant-produced material and aphid-produced material by the presence of other plant-derived terpenes, particularly ( )-caryophyllene, in the volatile blend. 

Host plants may influence sex pheromone behaviour in insects both in pheromone production and release and in the responses obtained (Landolt and Phillips, 1997). Food odour synergists or other host-plant derived semiochemicals may be incorporated in pheromone trapping systems to improve their performance (Phillips, 1997). The combination of sex pheromone and food odour probably has... 

Biopesticides include microbial living systems primarily based on bacteria, fungi and viruses. They may also include macro-organisms such as entomopathogenic nematodes, insect predators, and parasites. Biological pesticides may also include plant-derived metabolites as well as insect pheromones and most interestingly... 

The alarm pheromones of aphids often are sesquiterpenes such as ( )-3-famesene (71) and germacrene A (72) (Bowers, 1985). Upon release of these compounds, aphids drop from the plant on which they have been feeding. The compounds are very labile and break down in only a few minutes. This is important to prevent the aphids from being in a constant state of alarm (Bowers, 1985). Although this sesquiterpene elicits response in many species of aphids, the turnip aphid Lipaphis (Hyadaphis) erysimi responds only weakly. Addition of plant-derived isothiocyanates to p-famesene has a synergistic effect and greatly enhances the effect of P-famesene (71) (Dawson et al., 1987 Harbome, 1989). 

Dawson, G. W., D. C. Griffiths, J. A. Pickett, L. J. Wadhams, and C. M. Woodcock, Plant-derived synergists of alarm pheromone from turnip aphid, Lipaphis (Hyadaphis) erysimi (Homo-ptera, Aphididae), J. Chem. EcoL, 13, 1663-1671 (1987). 

Specialized lepidopterans not only sequester PAs from their host plants but also transform them into insect-specific metabolites. The two best-studied examples are the PA-derived pheromones and the so-called insect PAs. 

Mahroof RM, Phillips TW (2008) Responses of stored-product Anobiidae to pheromone lures and plant-derived volatiles. Journal of applied Entomology 132 161-167... 

Figure 6.8 The structure of myrcene and the aggregation pheromones of two species o/Ips beetles that are now found not to be made from plant-derived myrcene, but Ips paraconfusus males and females convert a-pinene to ds-verbenol...

Interestingly, the first biosynthetic experiments with [3H]linolenic add and the terrestrial plant Senecio isatideus (Asteraceae) as a model system for the biosynthesis of algal pheromones were unsuccessful. If, however, labeled dodeca-3,6,9-trienoic add is administered, a rapid transformation into ectocarpene takes place (36). Nevertheless, the C12 add ultimately derives from linolenic acid via three /3-oxidations, since labeled tetradeca-5,8,11-trienoic acid, which requires only one /3-oxidation, is converted into labeled ectocarpene albeit with very low effidency (37). 

Marine lipophilic semiochemicals are well known, in particular the C hydrocarbon pheromones of brown algae (Oldham 19%, Chart 8.2.FA/PO). Hydrophilic semiochemicals, which are more difficult to identify, are also emerging. Those from tobacco plants are the first known multiple polypeptide hormones deriving in plants from a polyprotein precursor, like in animals and yeast (Pearce 2001). 

In addition to mating-disruption pheromones, there are a number of naturally occurring, nonpheromonal attractants and repellents. Many are typically used as food additives or in cosmetics or perfumes, and are derived from diverse plant and animal sources. Capsaicin [44], the spicy component of chili peppers, is used in several bird, deer, and rodent repellents. Maple lactone [45], a common food additive and flavoring, is used in traps to attract cockroaches with its stale beer odor. Methyl... 

Some early and obvious questions about bark beetle pheromone components concerned their origins are they synthesized de novo from acetate or derived from plant precursor molecules And are the biochemical reactions performed by insect tissues or symbiotic bacteria Ipsdienol and ipsenol are clearly monoterpenoid alcohols. Since de novo monoterpenoid biosynthesis was unprecedented in the Metazoa before 1995, and monoterpenes are produced by host trees, it seemed logical that monoterpenoid pheromone components were derived from ingested plant precursor molecules (reviewed in Vanderwel and... 

Availability of biosynthetic precursors from food, as in some danaid butterflies and arctiid moths, which modify plant pyrrolizidine alkaloids into volatile derivatives that are used as male pheromones (e.g. Schneider et al., 1975). In... 

The CM of fatty acids and derived compounds also has been used for the production of fine chemicals that are difficult to obtain by other synthetic approaches. Some examples include the synthesis of a plant growth stimulant, an insect pheromone precursor, the sex pheromone of the peach twig borer moth, and others [28]. Furthermore, the conjugation of fatty acid derivatives, sugars, and amino acids via CM was shown by Vemall and Abell [41]. C4 with a catalyst loading of 20 mol% was used to perform the CM of either Ai-Boc-L-ly sine or N-Boc-L-cysteine bearing a 10-undecenoic chain with methyl 10-undecenoate or a sugar olefin. 

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