Sparse and stereotyped encoding implicates a core glomerulus for ant alarm behavior

Ants communicate via large arrays of pheromones and possess expanded, highly complex olfactory systems, with antennal lobes in the brain comprising up to ∼500 glomeruli. This expansion implies that odors could activate hundreds of glomeruli, which would pose challenges for higher-order processing. To study this problem, we generated transgenic ants expressing the genetically encoded calcium indicator GCaMP in olfactory sensory neurons. Using two-photon imaging, we mapped complete glomerular responses to four ant alarm pheromones. Alarm pheromones robustly activated ≤6 glomeruli, and activity maps for the three pheromones inducing panic alarm in our study species converged on a single glomerulus. These results demonstrate that, rather than using broadly tuned combinatorial encoding, ants employ precise, narrowly tuned, and stereotyped representations of alarm pheromones. The identification of a central sensory hub glomerulus for alarm behavior suggests that a simple neural architecture is sufficient to translate pheromone perception into behavioral outputs. [Display omitted] •An efficient transgenesis method for the clonal raider ant•Generation of a transgenic line expressing GCaMP6s in olfactory sensory neurons•Calcium imaging reveals highly stereotyped odor encoding in the ant antennal lobe•Alarm pheromones are sparsely encoded and activate a core glomerulus A transgenesis method for the clonal raider ant, yielding expression of the genetically encoded calcium indicator GCaMP6s in all olfactory sensory neurons, has shown how ants use spatially precise encodings for alarm pheromones.