Integration of odor and environmental CO2 information in the brain of the hawkmoth, Manduca sexta

It has been proposed that CO₂ cues from flowers play a role in the nectar-foraging behavior of adult moths. By combining physiological and behavioral research on moths, we are unveiling the informational value of CO₂ in a natural context. Our study system consists of the hawkmoth Manduca sexta and its southwestern host-plant Datura wrightii. We have previously demonstrated that CO₂ levels emitted by D. wrightii flowers upon anthesis are significantly greater than ambient concentrations, and that such elevated CO₂ levels, if emitted by false flowers, are sufficient to attract colony-bred moths in a laboratory setting. Like other adult moths, M. sexta possesses a specific and sensitive CO₂ detecting organ, the Labial Palp Organ (LPO), housed in the terminal segment of the Labial Palp. CO₂ detecting cells within the LPO send axons to a single glomerulus within the Antennal Lobe (AL) of the brain: the Labial Palp Organ Glomerulus (LPOG). The AL is well studied as the initial processing center for odor information relayed from receptor cells on the antenna. Interactions of neurons with in the LPOG and surrounding odor processing glomeruli thus represent the first potential site of odor-CO₂ integration within the nervous system. Here, we present recordings of neuronal responses in the AL of M. sexta in response to composite stimuli of D. wrightii floral odor blends or single components and elevated CO₂ levels. Our results indicate that CO₂ information is integrated with odor information by AL neurons.