Allomones, attractant

Abstract This chapter reviews chemical structures of biologically active, volatile compounds in beetles. Techniques used for structure elucidation are briefly discussed as well as facts and speculations on the biosynthesis of target compounds. Syntheses of selected substances are cursorily presented. The order of sections follows taxonomic classifications. Depending on the biological significance of relevant compounds in certain taxa, the corresponding sections are again subdivided into attractive compounds (mostly intraspecifically active pheromones) and defensive compounds (mostly interspecifically active allomones). 

The means by which many insects select a suitable host plant is by being attracted by plant secondary compounds that also serve as allomones. In other cases the insect may avoid the presence of a toxic compound by the correlated presence of other materials which may be repel 1 ant. 

The use of allomones to attract prey is not restricted to adult or last instar stages of M. hutchinsoni. Because juvenile spiderlings are too small to catch moths, they attract moth flies (Diptera Psychodidae). They do not use a bolas but instead seize their prey with their forelegs (Yeargan and Quate, 1996), and each spider species specializes on a specific prey species. Allomones that might mediate the attraction of prey have not yet been identified, and, indeed, the possible pheromones of psychodid moth flies are still largely unknown. To date, homosesquiterpene pheromones have been identified only from psychodid sandflies in the... 

Many hemipterans have metathoracic scent glands (e.g. Oetting and Yonke, 1978), which may produce both allomonal and pheromonal secretions. For example, females of Alydus eurinus release an attractant pheromone from their metathoracic scent gland (Aldrich et al., 2000). The internal scent gland apparatus of alydids... 

Aldrich J. R., Zhang A. and Oliver J. E. (2000) Attractant pheromone and allomone from the metathoracic scent gland of a broad-headed bug (Hemiptera Alydidae). Can. Entomol. 132, 915-923. 

Much less research has been done on food attractants than on sex pheromones. More emphasis on the understanding of such allomones and their potential use for insect control is needed. 

Defense is not the only use of allomones, however. Flowers use scent to attract pollinating insects. Honeybees, for instance, are guided to alfalfa flowers by a series of sweet-scented compounds. 

Behavior-modifying compounds are divided into two broad categories — pheromones and allelochemicals. A pheromone is a substance secreted by an animal that influences the behavior or development of other animals of the same species. The term was suggested by Butenandt, Karlson, and Liischer in 1959 (Butenandt et al., 1959 Karlson and Butenandt, 1959 Karlson and Liischer, 1959). Allelochemicals act between different species and are often called kairomones, provided that the recipient has an advantage by sensing the substance. If the substance only benefits the emitter species, the allelochemical is called an allomone, and if both emitter and receiver are benefited, the allelochemical is known as a synomone. The scent from flowers that attracts bees may therefore be called synomone. 

Camphor and <7-limonene are allomones in that the trees which produce them are protected from insect attack by their presence. For instance, Arthur Birch, one of the great terpene chemists of the twentieth century, reported finding d-limonene in the latex exuded by trees of the species Araucaria bidwilli.1 2 These trees are protected from termite attack because the d-limonene they produce is an alarm pheromone for termites that live in the same area. Similarly, antifeedants could be considered to be allomones since the signal generator, the plant, receives the benefit of not being eaten. Myrcene is a kairomone, in that it is produced by the ponderosa pine and its presence attracts the females of the bark beetle, Dendroctonous brevicomis. Geraniol is found in the scent of many flowers such as the rose. Its presence attracts insects to the flower and it can be classified as a synomone since the attracted insect finds nectar and the plant obtains a pollinator. 

The inter-specific mediators, or allomones, may work in one of two directions some are attractant, or allelostimulant, whilst others are repellent, or allelopathic. This distinction is not always clear, since the effects of such chemical mediation varies according to the receiving species within natural populations. It may, however, be retained for clarity of account. 

Defense is not the only use of allomones, however. Flowers use scent to attract pollinating insects. 

I. a. both species-specific pheromones and natural or synthetic foreign substances, provided that they possess insect-attracting properties, are used. o-MeAyl-eugenol, anisylacetone, geraniol/ eugenol have proved to be useful in various mixtures as I. a. for certain species. 4-(p-Hydroxyphenyl)-2-butanone (CI oH 12O2, Mr 164.20) and its acetate are commercially available as I. a. for the Mediterranean fruit fly Cera-titis capitata see also pheromones, allomones, syn-omones, kairomones, semiochemicals. 

KainmHMies. Name, derived from the Greek kairos (= favorable condition, advantage + hormone), for signalling substances ( semiochemicals) acting between individuals of different species with attractant effects, in contrast to within-species pheromones (see also al-lelochemicals, allomones, insect attractants), providing an advantage for the recipient. Example Predators of bark beetles locate their prey on the basis of the attractants produced by the latter to attract members of their own species. 

South American female Bolas spiders use an allomone blend, which contains the sex attractant (9Z)-tetradecenyl acetate of moths, to entice their prey imder false pretences , and then catch it with a sticky woven globule at the end of a silk thread, known as a bolas . By swinging the bolas with a foreleg at flying male moths nearby, the spider may angle its target rather like a fisherman snagging a fish on a hook. 

In other instances, compounds called kairomones are released by plants (or other organisms) and benefit the receiving organism. A number of these compounds serve as both repellent and attractant substances most kairomones probably originated as allomones. In any instance, it is possible for a compound to be an allomone with regard to many insects and a kairomone to others. More than 4000 compounds have been evaluated for their ability to attract several kinds of insects (Wright, 1966). Plant volatiles are only one factor in the attraction of animals to plants. Visual cues may also be extremely important (Stadler, 1983). 

Although cucurbitacins serve as allomones for most other insects, these compounds are kairomones, or attractants, for many insects associated with the Cucurbitaceae (Metcalf, 1985). For example, when cucumber beetles are offered a choice of nonbitter and bitter (cucurbitacin containing) fruits, they feed almost exclusively on the bitter fruits (11 1). When given the same choice, the honeybee. Apis mellif-era, will select food materials lacking the cucurbitacins (Har-bome, 1982). 

The interaction between pheromone-allomone-kairomone is also well established. For example, Anagasta kuhniella moths emit from the mandibular gland an epideitic (or a dispersal) pheromone which also induces parasitization by Venturia canescens 148). Sternlicht 149) reported that Aphytes mellinus and A. coheni, the two parasitic wasps of the coccid Aonidiella aurantii, were attracted by the sex pheromone... 

Behavioral Chemicals — Semiochemicals. Semiochemicals are chemicals emitted by plants or animals that modify the behavior of receptor organisms of the same or different species. This definition includes pheromones, allomones, and kairomones. The sex-attractant pheromones are emitted by the female to attract the male for mating purposes and they have been used in pest control in the following ways (11) ... 

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