Multicomponent pheromones

Probably the best-studied communication behavior in ants is chemical communication, but other sensory modalities, such as mechanical cues, also play an important role in the formation of multicomponent signals in ant communication. Chemical releasers are produced in a variety of exocrine glands, and considerable progress has been made in chemically identifying many of these glandular secretions (for reviews see refs. 1 and 2). In this essay I will not emphasize, however, the natural product chemistry of ant pheromones, but rather concentrate on the proposition that communication in ant societies is often based on multicomponent signals, on nested levels of variation in chemical and other cues, which feature both anonymous and specific characteristics (3). 

This long-chain unsaturated ester serves as one component of a mnlticomponent female sex pheromone for 140 species of moths as well as the Asian elephant. This is nnlikely to cause any real confnsion in nature. On the one hand, the 140 species of moths keep ont of each other s way and out of the elephant s way by varying the nature and relative concentrations of other components in the multicomponent pheromone. On the other hand, the male elephant is not likely to detect the extremely small amonnts of this pheromone released by female moths. Chemistry aside, there are other obvions difficnlties in moths mating with elephants in the wild. 

For mammals, if not vertebrates in general, multicomponent pheromones appear to be the rule. Such mixtures can comprise compounds of a wide range of volatility. They have been variously termed odor profile, pattern, odor image (Albone, 1984), gestalt (Evans ct al., 1978), or mosaic (Johnston, 2005). One of the best-investigated odor profiles is that of the scent mark of the saddle-back tamarin, S. fuscicoUis, (Smith et al, 1985). Here, not even the 16 butyrate esters are sufficient for subspecies recognition. Additional volatiles are also required. 

A second example of a mammalian multicomponent pheromone is the puberty-delaying pheromone from female house mice, Mus musculus. Two acetate esters and a pyrazine are biologically active in various combinations, but the pyrazine is also active alone (Novotny etal, 1985a). 

Shu S. and Jones R. L. (1993) Evidence for a multicomponent sex pheromone in Eriborus terebrans (Gravenhorst) (Hymenoptera Ichneumonidae), a larval parasitoid of the European com borer. J. Chem. Ecol. 19, 2563-2576. 

Francke W. (1986) Convergency and diversity in multicomponent insect pheromones. In Advances in Invertebrate Reproduction 4, eds M. Porchet, J.-C. Andries and A. Dhainaut, pp. 327-336. Elsevier Science Publishers, Amsterdam. 

An antennal-specific aldehyde oxidase (AOX) of M. sexta (MsexAOX) was the next identified pheromone-degrading enzyme (Rybczynski el al., 1989). The activity of MsexAOX was visualized on non-denaturing PAGE, and was shown to be antennal specific but present in sensilla of both male and female antennae. MsexAOX was observed as a dimer with a combined estimated molecular mass of 295 kDa. M. sexta uses a multicomponent pheromone consisting exclusively of aldehydes including bombykal (Starratt el al., 1979 Tumlinson el al., 1989, 1994) MsexAOX was shown to degrade bombykal to its carboxylic acid. Both TLC and spectrophotometric assays were established and a variety of substrates and inhibitors were characterized. Making adjustments for the concentrations and volumes within a sensillum lumen, the in vivo half-life of pheromone was estimated at 0.6 msec in the presence of this enzyme (Rybczynski el al., 1989). 

Picimbon J. F., Gadenne C., Becard J. M., Clement J. Land Sreng L. (1997) Sex pheromone of the French black cutworm moth Agrotis ipsilon (Lepidoptera Noctuidae) identifcation and regulation of a multicomponent blend. J. Chem. Ecol. 23, 211-230. 

For example, changes in the composition of the active ingredient caused either by degradation of the pheromone or a change in the ratio of components of a multicomponent formulation would not be detected by this method. 

Prior to delving into the details, this overview briefly summarizes the recent progress made as follows (1) progress in structure elucidation, (2) complexity of the multicomponent pheromone, (3) stereochemical aspects of chemical ecology, (4) dual roles of semiochemicals such as pheromones and kairomones, and (5) new trends in mammalian chemical ecology. 

Recently in 2008, Lacey et al.1 reported a typical example showing the complexity of a multicomponent pheromone. A male-produced aggregation pheromone of the cerambycid beetle Megacyllene caryae contained as... 

In addition to 3,1 l-dimethylnonacosan-2-one (M12) and 3,1 l-dimethylheptacosan-2-one, products of u>-oxidation, that is, 29-hydroxy-3,ll-dimethylnonacosan-2-one and 19,27-dimethyl-28-oxononacosanal (M37) as well as the two corresponding C27 compounds are components of a multicomponent contact pheromone contained in the cuticula of sexually mature females of the German cockroach B. germanica932... 

The male D. crlstata respond to 8-methyl-2-decanol acetate. However, when the four isomers of the acetate were tested, D. crlstata males responded only to the (2S,8R)-isomer (39). Thus both structural diversity and stereoisomerism are being used by this group of insects to achieve specificity in their chemical signals. NO evidence of multicomponent pheromones in this group has yet been discovered. 

The chirality of only one of these male produced pheromones has been determined, i.e. (Z)-3-dodecen-ll-olide. However, it appears that here again both multicomponent blends and chirality are being used to achieve specificity in the pheromone signals... 

The first insect sex pheromone to be identified was bombykol, (E,Z)-10,12-hexadecadien-l-ol [58]. The elucidation of the structure spanned 20 years and required half a million female abdomens. A few years later, (Z)-7-dodecenyl acetate was identified as the sex pheromone of the cabbage looper, Trichoplusia ni [59]. Silverstein worked on bark beetles, in which three terpenes were identified as a synergistic pheromone blend for Ips paraconfusus [60], and it became reeognised that most insect pheromones consisted of multicomponent blends. 

As the pheromones of fish and crustaceans become better understood, species specificity through multicomponent blends may be revealed (Stacey and Sorensen 2006). Multicomponent synergy, with two or more pheromone components needed together, has been demonstrated to stimulate a gonadotropin surge in male goldfish. 

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