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Olfactory pathway of the hornet Vespa velutina : New insights into the evolution of the hymenopteran antennal lobe

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Couto, Antoine | Lapeyre, Benoit | Thiéry, Denis | Sandoz, Jean-Christophe

Edité par CCSD ; John Wiley & Sons -

International audience. In the course of evolution, eusociality has appeared several times independently in Hymenoptera, within different families such as Apidae (bees), Formicidae (ants) and Vespidae (wasps and hornets) among others. The complex social organization of eusocial Hymenoptera relies on sophisticated olfactory communication systems. While the olfactory systems of several bee and ant species have been well characterized, very little information is yet available in Vespidae, although this family represents a highly successful insect group, displaying a wide range of lifestyles from solitary to eusocial. Using fluorescent labeling, confocal microscopy and 3D reconstructions, we investigated the organization of the olfactory pathway in queens, workers and males of the eusocial hornet Vespa velutina. First, we found that caste and sex dimorphism is weakly pronounced in hornets, both with regards to whole brain morphology and antennal lobe organization, although several male-specific macroglomeruli are present. The Vespa velutina antennal lobe contains about 265 glomeruli (in females), grouped in 9 conspicuous clusters formed by afferent tract subdivisions. As in bees and ants, hornets display a dual olfactory pathway, with two major efferent tracts, the medial and the lateral antennal lobe tracts (m- and l-ALT), separately arborizing two antennal lobe hemilobes and projecting to partly different regions of higher-order olfactory centers. Lastly, we found remarkable anatomical similarities between the glomerular cluster organizations of hornets, ants and bees, suggesting the possible existence of homologies in the olfactory pathways of these eusocial Hymenoptera. We propose a common framework for describing AL compartmentalization across Hymenoptera and discuss possible evolutionary scenarios.

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