Insect Olfaction edited by Bill Hansson

Springer, 1999. $293.00, £134.00, DM349.00 (457 pages)ISBN 3 540 65034 2Over the past five to ten years or so there has been a surge of interest in olfactory research (recently reviewed in Ref. 1xMaking sense of scents. Stern, P. Science. 1999; 286: 703–728Crossref | Scopus (3)See all ReferencesRef. 1). The organisms being used in cellular, molecular and behavioral studies of olfaction include birds, rats, salamanders, fish and nematodes. What advantages are offered by insects that we should pick their noses (and by extension, their brains) to further our understanding of the sense of smell? Insect Olfaction considers recent advances in olfactory research and in the process, reveals how the study of insect olfactory systems is providing insights into both specific and general olfactory principles. Although much of the book is obviously aimed at a specialist audience, it should be readily accessible to those interested in olfaction and sensory systems in general.Predictably we begin our olfactory journey at the periphery, looking down the insect nose. We start as an odor molecule might, observing the vast array of morphological shapes and forms of the insect antenna – those structures that insects employ as their nose. In comparison, they make human noses run of the mill. They range from the ordinary to extraordinary in their appearance, size and shape. Their morphological diversity is reflected by elegant monikers: in what other group could one chose between pectinate, serrate, geniculate, lamellate and plumose forms (to name a few)? A closer look reveals that many an antenna is densely covered with cuticular hairs that house the dendrites of olfactory-receptor cells. Despite the outward appearance of the olfactory epithelium, once we have traversed the waxy insect cuticle, the mechanisms used to transduce odorant molecules begin to take on a familiar tone: G-protein-coupled receptors and the usual host of second-messenger molecules appear to have a significant role in the initial phases of the cascade that results in the eventual generation of action potentials. The search for olfactory-receptor proteins in insects has lagged behind progress in vertebrates up until very recently. Insect Olfaction was printed around the time that molecular characterization of the first putative insect olfactory-receptor proteins in Drosophila occurred2xA novel family of divergent seven-transmembrane proteins: candidate odorant receptors in Drosophila. Clyne, P.J. et al. Neuron. 1999; 22: 327–338Abstract | Full Text | Full Text PDF | PubMedSee all References, 3xA spatial map of olfactory receptor expression in the Drosophila antenna. Vosshall, L.B. et al. Cell. 1999; 96: 725–736Abstract | Full Text | Full Text PDF | PubMedSee all References and some chapters are only briefly able to comment on this nascent development.The central destination for signals originating at the periphery are the antennal lobes, paired structures that each serve one antenna; these are the primary processing centres for olfactory signals in insects. A substantial part of Insect Olfaction is devoted to our current knowledge of the anatomy, circuitry, neuropharmacology and development of the antennal lobe. This focus is unsurprising because the organization of the antennal lobe into spheroidal knots of neuropil, known as glomeruli, is representative of the organization of olfactory systems in vertebrates as well. The insect antennal lobe therefore provides a relatively simple neuroanatomical correlate in which to investigate how the nervous system encodes and initially processes information about the olfactory environment.The antennal lobe is one of three ganglia that are thought to have coalesced over evolutionary time to form the insect brain. Once olfactory signals have been processed in the antennal lobe, they are sent on to the most complex of these three ganglia, the protocerebrum. Here, in the calyces of the mushroom body and the lateral protocerebrum, the trail grows cold in terms of olfaction. The complex circuitry and myriad connections between neurons in the mushroom bodies and other areas are just beginning to be unraveled, so for the time being, the secrets of the protocerebrum remain intact.Many insects are, of course, incredibly adept and athletic flyers, a locomotory feat that relies heavily upon the sense of vision. Because many insects respond and orient to odors on the wing, visual and olfactory information must be integrated at some level in the protocerebrum, a process that is far from understood. All is not lost, however. Back on the outside, we can take advantage of the many insect behaviors that are so clearly odor-mediated and our extensive knowledge of the actual chemical composition of attractive or repulsive odor blends. Probing the workings of the olfactory system and the maneuvres that are executed in getting from point A to point B provide additional hope of working our way from motor centers back up to those enigmatic higher integrative areas of the brain.To round things off Insect Olfaction considers the potential immediate applications of our understanding of insect olfaction and behavior as it relates to the control of harmful or agriculturally malevolent ‘critters’. But, as the bulk of this unique collection of chapters serves to note, insects are proving to be useful tools for studying the principles and development of the olfactory system in general. An honest attempt is made in most chapters to include what is known about insects other than Lepidoptera. Nevertheless, much of the book dwells upon Lepidoptera (particularly moths), honeybees and the molecular workhorse Drosophila, with mosquitoes and cockroaches (as is their natural wont) cropping up here and there. It is a small list of insects that does not really do justice to the massive diversity of insects on earth, but one that accurately reflects the current state of research into insect olfaction.