Integration of behaviourally relevant odours at the central nervous level of 3rd instar nymphal desert locusts, Schistocerca gregaria, showed phase- and (developmental) stage-dependent characteristics which correlated with differences in the number of olfactory sensilla. Antennal lobe (AL) neurons of gregarious locusts generally responded more frequently and showed a higher sensitivity to the tested stimuli. However, AL neurons of solitary locusts responded significantly more frequently to phenylacetonitril, the major component of the adult aggregation pheromone. Pheromone-specific, plant-specific and pheromone-plant generalist neurons were found in both phases. The response spectra of pheromone-specific neurons correlated with the potential behavioural significance of attractant chemical cues in the environment. Neurons of both phases responded specifically to stage-specific aggregation-pheromone components and to other chemical cues that may be involved in the location of suitable roosting and foraging sites.