FUNCTIONAL-ORGANIZATION OF THE MACROGLOMERULAR COMPLEX RELATED TO BEHAVIORALLY EXPRESSED OLFACTORY REDUNDANCY IN MALE CABBAGE-LOOPER MOTHS

The neurophysiological bases for behaviourally expressed olfactory red undancy in the sex pheromone communication system of the cabbage loope r moth, Trichoplusia ni (Hubner) (Lepidoptera: Noctuidae), were examin ed by coupling the cut-sensillum extracellular recording technique wit h a highly specific neuronal marking method for moth peripheral recept ors. In seventy-two antennal sensilla, axonal pathways of cobalt-stain ed neurones could be traced into the male-specific macroglomerular com plex in the antennal lobe. In T.ni males this comprises five glomeruli , two of which are subdivided into morphologically, and in some instan ces functionally identifiable, regions. Axonal arborizations of forty- eight neurones (single stainings) showed high fidelity (98%) for conta inment within a specific glomerulus or glomerular subdivision, and the neuropil targeted seemed to be related to the specificity of a neuron e to a particular female-emitted sex pheromone component (Z7-12:Ac, Z7 -14:Ac, Z9-14:Ac, 12:Ac, 11-12:Ac, Z5-12:Ac), or to a behavioural anta gonist (Z7-12:OH), Double (twenty-one) and multiple stainings (three) showed axons projecting into two or more glomeruli, respectively, with 100% fidelity for the component-specific glomerulus or glomerular sub division to be targeted. We suggest that the potential for a single mi nor component to cross-stimulate two or more neurones within a sensill um may enable partial blends to continue to provide sensory input into all of the pheromone-processing glomeruli of the complex. Our interpr etation is that redundancy occurs at the receptor level on neighbourin g dendrites, and thus allows various four-component partial blends to evoke full pheromone-mediated behaviour.