Semio-chemicals

The terminology used in this research area is not well established in the chemical community while the term pheromone is widely known, semio-chemical is not. Nevertheless, chemicals used in the communication between individuals are correctly called semiochemicals recently the equivalent term infochemicals was introduced. These compounds can be further divided into pheromones, compounds used in communication between individuals of the same species, while allelochemicals serve interspecific communication. Most pheromones are releasers, i.e. they provoke a behavioral change in the receiver. More rare are primers, which provoke physiological changes. Allelochemicals can be divided into kairomones, which are advantageous for the receiver, while the emitter benefits from allomones. Synomones are advantageous for both the emitter and the receiver. 

Pheromone identification is still difficult because the structure of unique compounds present in small amounts in mixtures of similar molecules has to be elucidated. This topic will be discussed in detail by Ando as well as by others, showing nicely the recent progress in analytical techniques. The following chapter by R. Jurenka deals with insect pheromone biosynthesis with special emphasis on lepidopteran pheromones and also covers genetic aspects. The subsequent chapter by C. Keeling et al. describes the hymenopteran semio-chemicals (bees and ants), describing pheromones and allelochemicals. The hymenoptera add a certain flavor to the scene, because now the complexity of social insects with their many interactions comes into play, as well as the multi-level (multi-trophic) signals used by parasitoids. 

Jones, K. A. and Kara, T. J. (1982). Behavioral response by Arctic chart (Salvelinus alpinus) to taurocholic acid and L-serine, two putative semio-chemicals. American Zoologist 22, 925. 

Experimental modulation of behavior of free-ranging mammals by semio-chemicals. In Chemical Signals in Vertebrates, vol. 3, ed. D. Muller-Schwarze, and R. M. Silverstein, pp. 235-244. New York Plenum. 

Limited evidence from microsurgical ablation experiments suggests that semio-chemicals are perceived by the external scapular setae (Leal el al., 1989f). The morphology of the setae has been characterized by scanning electron microscopy (Leal and Mochizuki, 1990). 

Females of the desert spider Agenelopsis aperta emit a volatile pheromone that attracts conspecihc males (Riechert and Singer, 1995). This pheromone was identified as 8-methyl-2-nonanone (1 Fig. 4.1), a previously unknown arthropod semio-chemical. It was found by headspace analysis and abdominal washings of females 2 weeks after their hnal molt, when they become sexually receptive it was absent in females of other age classes. The pheromone attracted males in a three-choice arena system at doses as low as 500 ng (Papke et al., 2001). Another female-specific ketone, 6-methyl-3-heptanone (2), was not attractive. Very low doses of 1 (10-9 mg/ml applied to a hlter paper placed in empty juvenile female webs) also induced courtship behavior in males (Papke et al., 2001). The normal behavioral sequence was followed, except for phases which required input from the female. The ED50 value (mean effective dose) of 1 was 5.5x 10-4 mg/ml hexane. In contrast, ketone 2 only induced a response in some males at unnaturally high concentrations... 

Rose, U.S.R., Manukian, A., Heath, R.R. and Tumlinson, J.H. (1996) Volatile semio-chemicals released from undamaged cotton leaves a systemic response of living plants to caterpillar damage. Plant Physiol., Ill, 487-95. 

BORDEN, J.H., Semio-Chemical Mediated Aggregation and Dispersion in the Coleoptera. Academic Press, London, 1984. 

Silverstein, R. M. (1979) Enantiomeric composition and bioactivity of chiral semio-chemicals in insects. In Chemical Ecology Odor Communications in Animals (Ritter, F. J., ed.). Elsevier/N. Holland, Amsterdam. 

In addition to separate analyses of consumption and growth efficiency, several other techniques have been used to quantify the relative importance of semiochem-icals on feeding behavior and postingestive physiology with varying levels of success. Some of these methods are summarized below. Because many of these methods are quite invasive and manipulative (i.e., direct injection of semio-chemicals, removal of taste receptors), they may alter the behavior or physiology of subjects substantially in their own right. 

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