1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

281 Poster Central Olfaction and Chemical EcologyENSEMBLE CODING OF ODOR-BLEND RATIOS IN THEINSECT ANTENNAL LOBEMartin J.P. 1 , Christensen T.A. 1 , Hildebrand J.G. 1 1 ARL Division ofNeurobiology, University of Arizona, Tucson, AZForaging insects use complex floral odor blends, consisting ofcommon odorants in specific ratios, to identify host plants. Little isknown about how the ratio of the components of a host-flower blend isrepresented in the antennal lobe, the primary processing center forolfactory information in insects. We investigated whether the responseof an ensemble of neurons in the antennal lobe of the moth Manducasexta was tuned to the natural ratio of components in the floral odor of ahost plant, sacred datura. Using a synthetic mixture of 14 majorcomponents of this blend, we presented mixtures with varyingconcentrations of single components, from 0.01 to 100 times the naturalconcentration. The components were also presented alone over the sameconcentration range. The firing rate of single units and recruitment ofadditional units both increased with the concentration of themonomolecular odorants alone, consistent with previous results.However, the response to the mixtures did not follow this predictedpattern. Instead, individual units exhibited an optimal response to themixture with the natural ratio of components, and deviatedsymmetrically from this optimum when the concentration of a singlecomponent was raised or lowered. The shape of the deviation wasfurthermore dependent on which component was altered. These resultssuggest that the representation of a blend in the antennal lobe is not asimple, linear combination of the component representations and thatthe glomerular circuit may be tuned to natural, behaviorally relevantratios of the component concentrations. Supported by NIH grant R01-DC-02751 to JGH.282 Poster Central Olfaction and Chemical EcologyCOMPARATIVE FUNCTIONAL MORPHOLOGY OF MALE-SPECIFIC GLOMERULI IN TWO HELIOTHINE MOTHSPECIES, HELICOVERPA ZEA AND HELIOTHIS SUBFLEXALee S. 1 , Carlsson M.A. 2 , Hansson B.S. 2 , Vickers N. 3 , Baker T.C. 11 Entomology, Pennsylvania State University, University Park, PA;2 Crop Science, SLU, Alnarp, Sweden; 3 Biology, University of Utah, SaltLake City, UTTwo sympatric heliothine species, Helicoverpa zea and Heliothissubflexa, share a major pheromone component, (Z)-11-hexadecenal(Z11-16:Ald). However, males are not attracted to interspecific femalesdue to the activity of minor components in heterospecific pheromoneblends. Action potentials from pheromone-component-sensitiveolfactory receptor neurons (ORNs) converge on specific glomeruli forfurther olfactory discrimination. We examined the morphological andphysiological characteristics of male-specific glomeruli with regard toORN excitation by different pheromone components in male H. zea andH. subflexa in order to delineate the glomeruli in the antennal lobe towhich each type of ORN projects its axons. For this research we usedthe cut-tip single sensillum recording technique followed by cobaltstaining to visualize glomerular targets of physiologically identifiedORNs. ORNs specifically responding to each component projectedconsistently to specific glomeruli in the olfactory lobe. Calciumimagingof component-specific glomerular activities in both speciescorroborated the cobalt stainings. We also described for the first time adistinct glomerular complex (“Posterior Complex”) in both specieswhose specific glomeruli are the arborization destinations of secondaryORNs co-compartmentalized with specific pheromone-sensitive ORNs.Supported by NSF IBN-9910783283 Poster Central Olfaction and Chemical EcologyOLFACTORY SHIFTS PARELLEL SUPERSPECIALISM FORTOXIC FRUIT IN A DROSOPHILA MELANOGASTER SIBLING,D. SECHELLIADekker T. 1 , Ibba I. 2 , Siju K. 2 , Stensmyr M. 2 , Hansson B. 2 1 SwedishUniversity of Agricultural Sciences, Alnarp, Sweden; 2 SLU, Alnarp,SwedenOlfaction in the fruitfly Drosophila melanogaster is increasinglyunderstood, from ligand–receptor–neuron combinations, to their axonalprojection patterns into the antennal lobe. Drosophila thus offers anexcellent opportunity to study the evolutionary and ecological dynamicsof olfactory systems. We compared the structure and function of thegeneralist D. melanogaster with that of specialist D. sechellia, whichoviposits exclusively on morinda fruit. Our analyses show that, whereasthe fruit´s headspace was dominated by acids, antennae responded moststrongly to hexanoates. D. sechellia exhibited an extraordinary strongresponse to methyl hexanoate (MeHex). Behaviorally D. sechellia wasmuch more attracted to these morinda fruit volatiles than D.melanogaster. The high sensitivity to MeHex was paralleled by a 2.5-3xoverrepresentation of MeHex neurons on the antenna and a concordant2.9 x increase in volume of the corresponding glomerulus as comparedto D. melanogaster. In addition, the MeHex neuron exhibited anextreme sensitivity down to femtograms of its ligand. In contrast, noperipherally-mediated shift was found paralleling D. sechellia`sincreased attraction to acids. These findings are a demonstration ofevolution acting at several levels in the olfactory circuitry in mediatinga fruitfly´s unique preference for fruit toxic to its sibling species.284 Poster Central Olfaction and Chemical EcologyRELEVANCE OF AGE, SEX, AND ODOR ON THE FORAGINGCAPABILITIES OF MANDUCA SEXTAWilliams A.K. 1 , Raguso R. 1 1 Biological Sciences, University of SouthCarolina, Columbia, SCForaging behavior of nectarivorous hawkmoths typically involvesbrief bouts of floral visitation. During these times, it is possible for theanimal to take up relatively large quantities of nectar with respect tobody weight. We are interested in the variation between the volume thatthe animals are capable of imbibing when immobilized versus thatwhich they will freely take up during flight. Additionally, we areinterested in the role that odor plays in the quantity of nectar imbibed aswell as the relevance of sex and age. Naïve Manduca sexta of bothsexes and from one to five days post-eclosion in age, were immobilizedby clamping the wings and force-fed by manually extending theproboscis into a 25% sucrose solution. The mass of the solution inaddition to the masses of the moths was determined before and aftereach session so as to obtain the total volume ingested. Hand-feedingswere conducted with and without the presence of bergamot oil. Anothercohort of moths was released, individually, into a flight cage containingmock flowers. Each mock flower contained an eppendorf tube, intowhich one ml of 25% sucrose solution was pipetted. All moths andtubes containing the solution were weighed before each session.Subsequent to the flight, the moths and the tubes of the flowers visitedwere weighed. As in the hand-feedings, flights were carried out withand without the presence of bergamot oil. At one day followingeclosion, hand-fed males ingested greater volumes on average thanfemales. By the end of the second day quantities imbibed were moreuniform between the two sexes.71