Female Periplaneta americana cockroaches emit two cooperatively working pheromone components, periplanone-B (PB) as a long-range attractant and periplanone-A (PA) as a short-range arrestant, and males develop enlarged glomeruli for processing them separately in the first-order olfactory center. Using intracellular recordings and neuronal labelings, we found that the Turkestan cockroach, Blatta lateralis, which is phylogenetically close to P. americana but having adapted to inground habitats, has an extraordinary large glomerulus. This is caused by drastic enlargement of the PB-responsive glomerulus but not the PA-responsive glomerulus during the late nymphal stage. The output neuron from the macroglomerulus is sensitive to both PA and PB, at a dose of only 0.1 fg. Nevertheless, B. lateralis males never exhibited courtship rituals in response to the presentation of periplanones or natural sex pheromone but exhibited courtship rituals in response to antennal contact with females. Our findings indicate that the unique behavioral ecology and habitats of B. lateralis are related to the functional unification of the pheromone processing system, opposite to the functional differentiation that often underlies species diversification.
Keywords: Antennal lobe; Arrestant; Insects; Projection neuron; Sex pheromone.
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