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Olfactory projection neurons convey information from the insect antennal lobe (AL) to higher brain centers. Previous reports have demonstrated that pheromone‐responsive projection neurons with cell bodies in the moth medial cell cluster (mcPNs) predominantly have dendritic arborizations in the sexually dimorphic macroglomerular complex (MGC) and send an axon from the AL to the calyces of the mushroom body (CA) as well as the lateral horn (LH) of the protocerebrum via the medial AL tract. These neurons typically exhibit a narrow odor tuning range related to the restriction of their dendritic arbors within a single glomerulus (uniglomerular). In this study, we report on the diverse physiological and morphological properties of a group of pheromone‐responsive olfactory projection neurons with cell bodies in the AL lateral cell cluster (MGC lcPNs) of two closely related moth species. All pheromone‐responsive lcPNs appeared to exhibit "basket‐like" dendritic arborizations in two MGC compartments and made connections with various protocerebral targets including ventrolateral and superior neuropils via projections primarily through the lateral AL tract and to a lesser extent the mediolateral antennal lobe tract. Physiological characterization of MGC lcPNs also revealed a diversity of response profiles including those either enhanced by or reliant upon presentation of a pheromone blend. These responses manifested themselves as higher maximum firing rates and/or improved temporal resolution of pulsatile stimuli. MGC lcPNs therefore participate in conveying diverse olfactory information relating to qualitative and temporal facets of the pheromone stimulus to a more expansive number of protocerebral targets than their mcPN counterparts. Olfactory output neurons from the moth antennal lobe transmit pheromone information to a variety of higher brain centers along several distinct pathways. Pheromone blend‐sensitive multiglomerular neurons originating in the lateral cluster send information directly to lateral and dorsal targets where integration with other olfactory pathways and sensory modalities may occur. [ABSTRACT FROM AUTHOR]

Long distance sexual communication in moths has fascinated biologists because of the complex, precise female pheromone signals and the extreme sensitivity of males to specific pheromone molecules. Progress has been made in identifying some genesinvolved in female pheromone production and in male response. However, we have lacked information on the genetic changes involved in evolutionary diversification of these mate-finding mechanisms that is critical to understanding speciation in moths and other taxa. We used a combined quantitative trait locus (QTL) and candidate gene approach to determine the genetic architecture of sexual isolation in males of two congeneric moths, Heliothis sub flexa and Heliothis virescens. We report behavioral and neurophysiological evidence that differential male responses to three female-produced chemicals (Z9-14:Ald, Z9-16:Ald, Z11-16:OAc) that maintain sexual isolation of these species are all controlled by a single QTL containing at least four odorant receptor genes. It is not surprising that pheromone receptor differences could control H. sub flexa and H. virescens responses to 29-1 6:Ald and 29-14:Ald, r,espectively. However, central rather than peripheral level control over the positive and negative responses of H. sub flexa and H. virescens to Z11-16:OAc had been expected. Tight linkage of these receptor genes indicates that mutations altering male response to complex blends could be maintained in linkage disequilibrium and could affect the speciation process. Other candidate genes such as those coding for pheromone binding proteins did not map to this QTL but there was some genetic evidence of a QTL for response to Z11-16:OH associated with a sensory neuron membrane protein gene. [ABSTRACT FROM AUTHOR]

Shifts in male preference for qualitatively different pheromone blends appear to have played a fundamental role in the divergence of olfactory communication and evolution of moth species. As an initial step in documenting the genetic complexity underlying such shifts, we characterized the behavioral responses of hybrid male moths created by mating two heliothine moth species, Heliothis subflexa and Heliothis virescens. Between 67 and 96% of hybrid males flew upwind and contacted the pheromone source when presented with a blend consisting of (Z)-11-hexadecenal (Z11–16:Ald), (Z)-9-hexadecenal (Z9–16:Ald), and (Z)-11-hexadecenol (Z11–16:OH) in a 1:0.5:0.1 ratio that has previously been shown to be attractive to H. subflexa males. In addition, an H. virescens blend of Z11–16:Ald and (Z)-9-tetradecenal (Z9–14:Ald) enhanced by the addition of Z11–16:OH (in a 1:0.05:0.1 mixture) was attractive to hybrid males (26–64% source contact), but significantly fewer males reached the odor source compared to the blend containing Z9–16:Ald. A blend in which the dosage of Z9–14:Ald was doubled, however, was equally attractive (75–77% source contact) as the Z9–16:Ald-containing blend. Consecutive presentation of two blends revealed that individual hybrid males responded equally well to blends containing either Z9–14:Ald or Z9–16:Ald. Together these results suggest that in addition to Z11–16:Ald, hybrid males: (1) required either Z9–16:Ald (likeH. subflexamales) or Z9–14:Ald (like H. virescens males); (2) required the presence of Z11–16:OH (H. subflexa dominant); (3) were not adversely affected by the presence of Z11–16:Ac (H. subflexa dominant). The behavioral response phenotype of hybrid males was therefore influenced by genetic factors inherited from both parental species. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Pheromone-responsive olfactory interneurons were studied to determine the extent to which their physiological and morphological properties complemented the behavior and peripheral olfactory neurobiology observed in hybrid male moths created by interbreeding two species of heliothine moth, Heliothis virescens and Heliothis subflexa. Complete recordings were made from a total of 33 neurons, and 16 projection neurons (PNs) were subsequently stained with a fluorescent dye. Stained PNs tuned to pheromonal odorants had dendritic arborizations restricted to one of four olfactory glomeruli that together constituted the macroglomerular complex (MGC). As in parental males, PNs tuned to (Z)-11-hexadecenal always had an arbor in the cumulus, the largest of the MGC glomeruli. Previous neurophysiological investigations revealed that PNs with dendritic arbors restricted to the dorso-medial glomerulus (DM) of the MGC responded specifically to either (Z)-9-tetradecenal (Z9–14:Ald; H. virescens males) or (Z)-9-hexadecenal (Z9–16:Ald; H. subflexa males). Hybrid males, which responded equally well in wind tunnel tests to blends containing either Z9–14:Ald or Z9–16:Ald, had DM PNs that responded to both odorants. PNs specific for a third compound, (Z)-11-hexadecenol, required by hybrid males for behavioral activity were localized to the antero-medial MGC glomerulus (AM). Thus, neuronal activity across the cumulus, DM and AM glomeruli represented an attractive blend in hybrid males. Neurons tuned to (Z)-11-hexadecenyl acetate and Z9–14:Ald were restricted to a fourth, ventro-medial glomerulus. The across-glomerular pattern of activity associated with attractive pheromone blends was most similar to that of H. subflexa males, signifying a dominant effect of H. subflexa genes. These results indicate that the behavioral phenotype of hybrid males can be linked to underlying central olfactory characteristics. Copyright © 2006 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

In different moth species, the number and spatial arrangement of olfactory glomeruli in the antennal lobe (AL) vary widely, but the spatial map within a species is thought to be invariant, making it possible to identify single glomeruli across individuals. We investigated the relationship between the physiological tuning of pheromone-selective interneurons and their association with specific, identified glomeruli in the macroglomerular complex (MGC) of the noctuid moth, Heliothis subflexa. Three odorants that are required for pheromone-source location in this species were tested individually and in blends. Recordings from 27 pheromone-specific projection neurons (PNs) indicated that the majority (48%) were selectively activated by the major pheromone component of this species, Z-11-hexadecenal (Z11–16:Ald), with 33% primarily tuned to Z-9-hexadecenal and 19% to Z-11-hexadecenol. Intracellular staining revealed that the dendrites of PNs tuned to Z11–16:Ald always branched within the largest glomerulus of the MGC, the cumulus. Similarly, each of the other two classes of PN was associated with a different `satellite' glomerulus in the MGC. The spatial configuration of the four-glomerulus H. subflexa MGC was indistinguishable from that previously reported in the closely related species, Heliothis virescens. Hence, as these two species diverged, changes in the association of satellite MGC glomeruli with particular odorants have occurred without a measurable change in the anatomical arrangement of the glomerular array. [ABSTRACT FROM AUTHOR]