Central nervous processing of sex pheromones in two strains of the European corn borer Ostrinia nubilalis (Lepidoptera: Pyralidae).
Antennal lobe neurons were investigated in the pyralid Ostrinia nubilalis using intracellular recording and staining techniques. Response characteristics of antennal lobe neurons from males in the so-called E and Z strains, in F1 hybrids and in parental backcrosses were studied. The antennal lobe of a male O. nubilalis comprises approximately 30 ordinary glomeruli and three enlarged glomeruli making up the macroglomerular complex (MGC). Receptor neurons enter the antennal lobe via the antennal nerve and arborize in single glomeruli. Intracellularly stained, pheromone-responding projection neurons in both parental strains arborized in different glomeruli within the MGC, irrespective of their response characteristics. Neurons were grouped according to their specificity to single pheromone components and to pheromone blends. Component-specific, blend-specific and generalist neurons were found. Specificity only occurred at low stimulus concentrations and disappeared as concentrations increased. Although all neuronal types were present in both pheromone strains and crossings, differences in abundance and sensitivity were found. In the parental strains, neurons responding to the major pheromone component and to the respective strain-specific blend were more abundant than neurons responding to the minor component and the blend produced by the other strain. neurons investigated in Z × E hybrids responded similarly to those of E-strain males, whereas neurons in EZ × Z paternal backcrosses responded similarly to those of Z males. In the hybrids and paternal backcrosses, hybrid-blend-specific neurons were present that were not found in parental-strain males.