HIGH SPECIFICITY TO UBIQUITOUS SEMIOCHEMICALS: THE NORM ACROSS DIVERSE INSECT TAXA.

John A. Pickett, Lester J. Wadhams and Christine M. Woodcock
IACR-Rothamsted, Harpenden, Hertfordshire, AL5 2JQ

There is a great deal of evidence in the literature, from electrophysiologicalstudies through to field behaviour, of the high specificity of responsesto insect pheromones and to semiochemicals associated with host interactionswhere narrow taxonomic ranges are involved. Indeed, most of suchspecific interactions can be tied to molecular recognition processes atindividual sensory nerve cells. However, beyond specific host andmate recognition compounds are a wide range of ubiquitous semiochemicalssuch as the green leaf volatiles from plants and amino acid catabolitesfrom animal hosts. It has often been suggested that such semiochemicalsare detected by generalist receptor systems, and that the associated behaviouralresponses relate to groups of these compounds rather than to individualstructures. We have now accumulated evidence, from a wide range ofinsect taxa including phytophagous Coleoptera and Homoptera, haematophagousDiptera and beneficial insects from the Hymenoptera, that with ubiquitoussemiochemicals produced by widely ranged host species, the basis of theinteractions is a highly specific molecular recognition process involvingsensory cells with extremely narrow ranges of structural sensitivity andwith response thresholds similar, for example, to the pheromone recognitionsystems.