PHEROMONE-RELATED OLFACTORY NEURONAL PATHWAYS OF MALE HELIOTHINE MOTHS

Open Access
- Author:
- Lee, Seong-Gyu
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 24, 2006
- Committee Members:
- Thomas Charles Baker, Committee Chair/Co-Chair
James Homer Tumlinson Iii, Committee Member
James Lewis Frazier, Committee Member
James Harold Marden, Committee Member - Keywords:
- Helicoverpa zea
Heliothis virescens
Insect olfaction
Single-sensillum recording
Olfactory receptor neuron - Abstract:
- Two sympatric species of heliothine moths, Helicoverpa zea and Heliothis subflexa were used to study aspects of sex pheromone olfaction. The objective of my research was to increase our understanding of the functional morphology of the sex pheromone olfactory pathways of these species, focusing on the portion occurring at the level of the antennal olfactory receptor neurons (ORNs) and their axonal projections into specific glomeruli in the antennal lobe of the brain. My research showed that each type of ORN that responds to a particular pheromone-related compound and housed in specific sensillar types projects with nearly 100% fidelity to a particular glomerulus in the macroglomerular complex (MGC) of the antennal lobe in both species. My findings show that in these noctuid species, the pheromone-component-specific olfactory pathways are linear. The ORNs of both species that are tuned to the major pheromone component, (Z)-11-hexadecenal (Z11-16:Ald) project their axons to a specific glomerulus, the cumulus, with no exceptions. I also found that the second and third pheromone-related sensilla types in both species projected their axons to the other smaller glomeruli comprising the MGC. During the cobalt staining studies of Z11-16:Ald-tuned ORNs in both H. zea and H. subflexa, I found that there were often secondary, “unresponsive” neurons that also became stained, and these consistently arborized in a particular glomerulus situated posterior to the MGC. I recognized that this glomerulus resided in a previously overlooked cluster of glomeruli, which I named the Posterior Complex, or “PCx”. The specific glomerulus in which these secondary ORNs arborized I named “ PCx1”. In H. subflexa, there was also a second type of unresponsive ORN that was co-compartmentalized with the ORN tuned to Z9-16:Ald and which consistently projected to another specific glomerulus in the H. subflexa PCx, which I named the PCx4. For both species, in the process of using large arrays of different classes of odorant molecules to determine whether these secondary ORNs were truly unresponsive, I found that these very small-spiking ORNs exhibited significantly increased spike frequencies whenever the large-spiking ORN responded to Z11-16:Ald.