Interactions of mechanical stimuli and sex pheromone information in antennal lobe neurons of a male moth, Spodoptera littoralis

Abstract

Male moths respond to sex pheromone sources with up-wind flight behaviour. Localization of the odour source requires not only detection of the olfactory stimulus, but also other sensory input regarding, e.g. visual and mechanical stimuli. Thus, integration of different types of sensory input is necessary. It is, however, not known where in the central nervous system the integration of information regarding different sensory modalities takes place. Using intracellular recording and staining techniques, we investigated neurons in the antennal lobe of Spodoptera littoralis, during stimulation with a mechanical stimulus and a sex pheromone. Fifteen percent of all the neurons investigated responded to the mechanical stimulus and the majority of these neurons showed altered responses if the olfactory stimulus was added. A receptor neuron responding only to the wind stimulus was found to arborise in the antennal lobe. Most projection neurons responded with an enhanced action potential frequency to the combined stimulus. In local interneurons, enhancement, depression, or no change of the responses to the wind stimulus was found when the olfactory stimulus was added. The results suggest that neurons present in the antennal lobe integrate mechanosensory and olfactory input, possibly assisting the moths to orient during up-wind flight towards an odour source.