Mapping of Central Pathways for CO2 Information in the Brain of the Moth Heliothis virescens

Abstract

The olfactory system is vital for insects in their ability to seek food, reproduce, and orientate. Information about different odors, produced by plants or conspecifics, elicits behavioral responses in the insects. Knowledge about how chemical substances change the insects? behavior may be used in development of pest-specific and biologically harmless insecticides. One biologically relevant odor cue is carbon dioxide (CO2). This master?s project used the noctuid moth Heliothis virescens as model organism for mapping the central neural pathways involved in processing of CO2 information. By injecting dye into the CO2 sensory organ on the labial palps, it was possible to visualize the labial pit organ glomerulus (LPOG) in the antennal lobes of living individuals. Subsequent retrograde stainings of the LPOG revealed distinct projection pathways to higher brain centers. The stained projection neurons were demonstrated to follow two of the main antenno-protocerebral tracts; the lateral- and the medio-lateral antenno-protocerebral tract. Both of the neural bundles showed extensive branching in the protocerebrum. Two main termination areas were found to receive information from the LPOG; the lateral- and superior protocerebrum. No projection neurons followed the route via the medial antenno-protocerebral tract to the mushroom body calyces. This indicates that information about CO2 is processed only by an experience-independent pathway. All projection neurons originating from the LPOG were found to be uniglomerular, also those passing in the medio-lateral tract. This is in contrast to findings related to the general olfactory system where the last mentioned tract includes fibers of multiglomerular projection neurons. Comparison of the CO2 pathways in males and females showed no indications of sexual dimorphism. In total, the results from this study show significant differences between the general olfactory system and the CO2 system of H. virescens.