Spatial Representation of Feeding and Oviposition Odors in the Brain of a Hawkmoth.

Female hawkmoths, Manduca sexta, use olfactory cues to locate nectar sources and oviposition sites. We investigated if the behavioral significance of odorants is represented already in the antennal lobe, the first olfactory neuropil of the insect's brain. Using in vivo calcium imaging, we first established a functional map of the dorsal surface of the antennal lobe by stimulating the moths with 80 ecologically relevant and chemically diverse monomolecular odorants. We were able to address 23 olfactory glomeruli, functional subunits of the antennal lobe, in each individual female. Next, we studied the relevance of the same odorants with two-choice experiments (odorant versus solvent) in a wind tunnel. Depending on odorant identity, naive moths made attempts to feed or to oviposit at the scented targets. A correlation of wind tunnel results with glomerular activation patterns revealed that feeding and oviposition behaviors are encoded in the moth's antennal lobe by the activation of distinct groups of glomeruli.