Podcast with Bill Hansson on insect olfaction and antennal lobe

How do flowers deceive insects into pollinating them , and what does this reveal about how olfactory systems encode meaning? Bill Hansson explores the evolutionary arms race between plants and pollinators through the lens of insect chemosensory neuroscience. Subscribe for more from the Convergent Science Network podcast series. Bill Hansson studies olfaction in insects, and his entry point is one of nature's most elaborate deceptions. One-third of all orchid species are deceptive , they attract pollinators without offering nectar rewards, instead mimicking the chemical signatures of food, mates, or egg-laying sites with extraordinary precision. Hansson describes flowers that replicate the individual odor variation of female bees so accurately that males never learn to avoid them, and Mediterranean lilies that mimic both the volatile chemistry and the elevated temperature of rotting flesh to lure egg-laying flies into their chambers. These deceptive systems serve as powerful experimental tools. Because evolutionary pressure demands that the mimicry be nearly perfect, deceptive flowers effectively reveal which chemical features matter most to the insect brain. Hansson's laboratory uses this insight in reverse: by identifying the behaviorally relevant compounds through the deception, they can probe the olfactory system with precisely the stimuli it evolved to detect. The approach has been transformed by advances in single-neuron electrophysiology and optical imaging of the antennal lobe , the insect brain's first olfactory processing center. A surprising finding emerges from comparing input and output patterns in the Drosophila antennal lobe. At the receptor neuron level, there is no clear clustering of activation patterns by behavioral valence , attractive and repulsive odors look similar. But at the projection neuron output, attractive and repulsive patterns separate cleanly. This suggests the antennal lobe performs a valence-sorting operation, not just odor discrimination, before information even reaches the mushroom bodies traditionally associated with learning and memory. Hansson speculates that this early valence coding may serve the direct pathway to the lateral horn, which bypasses the mushroom bodies entirely and may mediate reflexive behavioral responses. The interview also examines a remarkable case of evolutionary specialization in Drosophila sechellia, a species that feeds exclusively on a single toxic fruit. This fly has sacrificed several receptor types used by its generalist relatives and massively expanded both the peripheral neurons and the central brain regions dedicated to detecting its host fruit , achieving detection thresholds rivaling moth pheromone systems at picogram concentrations.