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An essential part of sexual reproduction typically involves the identification of an appropriate mating partner. Males of many moth species utilize the scent of sex pheromones to track and locate conspecific females. However, before males engage in flight, warm-up by shivering of the major flight muscles is necessary to reach a thoracic temperature suitable to sustain flight. Here we show that Helicoverpa zea males exposed to an attractive pheromone blend (and in some instances to the primary pheromone component alone) started shivering earlier and took off at a lower thoracic temperature than moths subjected to other incomplete or unattractive blends. This resulted in less time spent shivering and faster heating rates. Two interesting results emerge from these experiments. First, the rate of heat generation can be modulated by different olfactory cues. Second, males detecting the pheromone blend take off at lower thoracic temperatures than males exposed to other stimuli. The take-off temperature of these males was below that for optimal power production in the flight muscles, thus generating a trade-off between rapid departure and suboptimal flight performance. Our results shed light on thermoregulatory behaviour of unrestrained moths associated with the scramble competition for access to females and suggest ecological trade-offs between rapid flight initiation and sub-optimal flight performance. [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]