Pheromones chemical specificity

Sorensen, P. W., Stacey, N. E., and Kara, T. J. (1990b). Acute olfactory sensitivity and specificity of mature male goldfish to water borne androgenic steroids a class of inhibitory pheromones. Chemical Senses 15,644. 

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. 

Vertebrates possess three primary chemosensory systems gustation ( taste ), trigeminal, and olfaction ( smell ) but only one of these, the olfactory system, mediates responses to pheromones. Chemicals that stimulate the olfactory system are known as odorants and comprise one type of biological cue (any entity that stimulates a sensory system). Bouquets of odorants that can be discriminated as specific entities are termed odors. The olfactory system contains olfactory receptor neurons (ORNs) that comprise cranial nerve I and project directly to the forebrain. ORNs are now known to express only one to a few olfactory receptor proteins ( receptors ), which means that the chemoreceptive range of each neuron can be very narrow. The olfactory system also has several subcomponents including the vomeronasal organ, which is described below. 

The frequent occurrence of pheromonal mimics in plants is disturbing in view of the oft-presumed specificity of pheromonal chemicals. One might wonder whether their presence in plants has communicative significance for cockroaches. A defensive strategy based upon the possession of a sex pheromone mimic seems of dubious value to a plant unless the stimulation to sexual activity overrides or depresses feeding activities. Alternatively, attraction of omnivorous cockroaches might result in their destruction of competing plants or parasites. 

Klun et al. 267), in studies at Ankeny, Iowa, on the European corn borer, found that males were only weakly attracted to highly purified (Z)-l 1-tetradecenyl acetate while the red-banded leafroller was not attracted at all to this compound. However, if small amounts of the E-isomer were added to the Z-isomer, both species were strongly attracted, yet neither species showed any response to the E-isomer alone. It was primarily after this study that it was realized that many lepidopteran sex pheromones are specific blends of the E- and Z-isomers of long chain acetate esters. The results on the Iowa European corn borer have recently been confirmed by more sophisticated separation techniques for chemically complex mixtures 268) and a number of specific ratios of the nonpheromone, (Z)- and ( )-ll-tridecenyl acetate, have been studied in field trials on the red-banded leafroller 269). 

Lepidoptera is the second largest insect group and includes nearly 150,000 described species, which have evolved over 100 million years since the Mesozoic era. For the birth of a new species, it must be isolated from other species by some factor to prevent inter-species crossing. The sex pheromone, which is secreted by the adult (usually by a female moth and sometimes by a male moth or butterfly) for the benefit of a specific partner, plays an important role in reproductive isolation. Therefore, it is no wonder that the chemical structures of the species-specific pheromones exhibit considerable differences. 

It is most unusual for female moths to utilize just one compound as the pheromone. Rather a blend of compounds produced in precise ratios make up the species-specific pheromone. The production of this precise blend of chemical components is regulated in the biosynthetic pathway. The inherent specificities found within key enzymes in the pathway and combinations of enzymes is what is responsible for producing species specific ratios [13,31]. 

This chapter reviews the literature of semiochemical (mostly pheromone) identification in Hymenoptera published since 1990. For this review, we separate the order Hymenoptera into the following three, somewhat overlapping, classes to reflect their differences in biology and semiochemistry solitary, parasitic, and social (Table 1). Although there is considerable literature on the semiochemical activity of specific glandular extracts and the chemical composition of specific glands, only those chemicals with demonstrated pheromonal (or semiochemical) activity will be specifically discussed here. The earlier literature of pheromones in social hymenoptera has previously been reviewed [4-6]. There have been more recent reviews of pheromones in social hymenoptera [7-10], parasitic wasps [11,12], sawflies and seed wasps [13,14], and mating pheromones across Hymenoptera [15]. 

Unlike parasitoids of other insect orders that have host-seeking larvae, most parasitic hymenoptera lay their eggs on, in, or very close to a host individual [11]. This requires the adult female to find a suitable host, often with the aid of chemical cues from host frass, pheromones, plant volatiles emitted upon host feeding or egg-deposition, silk, honeydew and other secretions. She may then chemically mark the host following oviposition to reduce superparasitism by herself or intra- and inter-specific insects [11]. 

Claims of commercial manufacturers notwithstanding, it is evident that pheromones do not function as behavioural releasers in humans in the same way as they do in other species. Instead of searching for specific reactions to purported human pheromones, it may be that these chemicals are better described as modulators (Jacob and McClintock 2000) which influence psychological states and, thereby, also influence behaviour in a variety of fashions depending on the situation in which they are experienced, or the accompanying cues. The co-occurrence of different cues can affect their interpretation (Rowe 1999). In humans, we know that odour cues provide non-redundant information about potential mates because, while both visual and olfactory cues may be used to gauge physical attractiveness, the information in each is not equivalent (Roberts, Little, Gosling, Jones, Perrett, Carter and Petrie 2005). 

In conclusion, the reliable, functionally vital and stereotyped nature of the pups response to the chemical signal governing nipple-search behaviour would seem to qualify this as a true mammalian releasing pheromone (Beauchamp, Doty, Moulton and Mugford 1976) and particularly as it appears to be species-specific rabbit pups fail to respond to lactating cats, rats, guinea pigs or even hares with nipple-search behaviour or nipple attachment (Muller 1978 Hudson 1985 own observations). 

In short, the present situation regarding these two, differently named pheromones can be briefly summarized as follows. With the nipple-search pheromone we have a chemical signal with a clear survival function in a biologically relevant context but still chemically unidentified. With the mammary pheromone we have a single substance which undoubtedly releases specific responses within a certain range of concentrations but the function of which, in a biologically relevant context, still has... 

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). 

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