Olfactory coding in the bumble bee antennal lobe

Abstract

Sociality is classified as one of the major transitions in evolution, with the largest number of eusocial species found in the insect order Hymenoptera, including the Apini (honey bees) and the Bombini (bumble bees). Bumble bees and honey bees not only differ in their social organization and foraging strategies, but comparative analyses of their genomes demonstrated that bumble bees have a slightly less diverse family of olfactory receptors than honeybees, suggesting that their olfactory abilities have adapted to different social and/or ecological conditions. However, unfortunately, no precise comparison of olfactory coding has been performed so far between honey bees and bumble bees, and little is known about the rules underlying olfactory coding in the bumble bee brain. In this study, we used in vivo calcium imaging to study olfactory coding of a panel of floral odorants in the antennal lobe (AL) of the bumble bee Bombus terrestris. Our results show that odorants evoke consistent neuronal activity in the bumble bee antennal lobe. Each odorant evokes a different glomerular activity pattern revealing this molecules chemical structure, i.e. its carbon chain length and functional group. Response intensity as well as odor-similarity relationships were highly correlated to those measured in honey bees. This study thus suggests that bumble bees, like honey bees, are equipped to respond to odorants according to their chemical features.