Central processing of aggregation pheromones in solitary and gregarious desert locusts, Schistocerca gregaria

In the desert locust, Schistocerca gregaria, a number of behaviorally active aggregation pheromone components have been identified from adult male S. gregaria, and from third, fourth and fifth instar nymphs. Adult females seem not to produce aggregation pheromones. Adult males and females, but not nymphs respond to the adult male-produced mixture, whereas only nymphs respond to the binary nymph-produced mixture with aggregation behavior. We studied the structure and function of antennal lobe interneurons, responding to single aggregation pheromone components and adult- and nymph-specific mixtures. Neurons in adult males and females and in first instar nymphs of S. gregaria in the solitary and the gregarious phase were investigated. Projection neurons responded with different degrees of specificity to all behaviorally active aggregation pheromone components. Component-specific, blend-specific and generalist neurons were found in adults and first instar nymphs in both phases. Antennal lobe neurons were slightly more sensitive in solitary than in gregarious locusts. In gregarious adult males and females more neurons responded to the adult male mix than to any of the single components. In gregarious first instar nymphs most neurons responded to the adult male mix and the major component but also nymph mix specific neurons were found. The behavior of adults and nymphs is thus partially reflected by the response characteristics of antennal lobe projection neurons.