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Summary. The purview of chemical ecology and the recent criticisms of improper application of theory to bark beetle phenomena is briefly discussed. Seven levels of research in chemical ecology are presented as well as their relationship to research on bark beetles. The biology and chemical ecology of several pest bark beetles from North America and Europe are discussed in regard to host tree selection theories of random landing on trees or attraction to semiochemicals. The diversity and similarities of pheromone components among species are presented in relation to their biosynthesis from host tree precursors and in relation to the ecological implications of de novo or precursor syntheses. Individual variation in biosynthesis of, response to, and release of pheromones is discussed. Olfactory perception of semiochemicals at both the electrophysiological and behavioral levels is presented. Orientation to semiochemicals during walking and flying is discussed with reference to the significance of dose-response curves for determining a compound's functionality in short-or long-range communication. The regulation of attack density, termination of the aggregation, mechanisms of attack spacing, and recognition of host suitability are presented in the context of an individual's avoidance of intra-and interspecific competition. Finally, a brief summary of topics where our understanding of the chemical ecology of bark beetles and their associates is poorly known is presented.Key words'. Scolytidae; semiochemical; pheromone; allomone; kairomone. Chemical ecology and ecologyEcology is the science of the relations of an organism to both its biotic and abiotic environment which influence the organisms' distribution and abundance w. The biotic factors are included in the disciplines of physiology, behavior, genetics and evolution; ecology is especially concerned with the interface of these areas. Chemical ecology then concerns any aspect of ecology but involves the external chemicals which mediate the interactions. This definition is actually more comprehensive than many would accept, for instance, it could include macrophage antibody microbe interactions, nutrient cycling, and much of biology. Traditionally, chemical ecology has been restricted to studies of the chemicals (semiochemicals) which mediate interactions between individuals of a species (pheromones) or between co-evolved species (allelochemicals, such as kairomones and allomones). Alcock 1 criticized several bark beetle (Scolytidae) researchers for what he thought was their inadequate application of ecological theory in the explanation of bark beetle phenomena. His primary concern was that bark beetle mass-attack and colonization of host trees was often misunderstood in terms of 'species-selection' when in fact 'individual selection' was now the dominant theory. Today most realize that a deeper knowledge of bark beetle biology can be obtained if both the proximate and ultimate causes for the phenomena are considered. Levels of research in chemical ecologyResearch in ...

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Plants release volatiles in response to caterpillar feeding that attract natural enemies of the herbivores, a tri-trophic interaction which has been considered an indirect plant defence against herbivores. The caterpillar-induced plant volatiles have been reported to repel or attract conspecific adult herbivores. To date however, no volatile signals that either repel or attract conspecific adults under field conditions have been chemically identified. Apple seedlings uniquely released seven compounds including acetic acid, acetic anhydride, benzyl alcohol, benzyl nitrile, indole, 2-phenylethanol, and (E)-nerolidol only when infested by larvae of the light brown apple moth, Epiphyas postvittana. In field tests in New Zealand, a blend of two of these, benzyl nitrile and acetic acid, attracted a large number of conspecific male and female adult moths. In North America, male and female adults of the tortricid, oblique-banded leafroller, Choristoneura rosaceana, were most attracted to a blend of 2-phenylethanol and acetic acid. Both sexes of the eye-spotted bud moth, Spilonota ocellana, were highly attracted to a blend of benzyl nitrile and acetic acid. This study provides the first identification of caterpillar-induced plant volatiles that attract conspecific adult herbivores under natural conditions, challenging the expectation of herbivore avoidance of these induced volatiles.

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