BilL. S. Hansson

▪ Abstract The antennal lobe of insects has emerged as an excellent model for olfactory processing in the CNS. In the present review we compile data from areas where substantial progress has been made during recent years: structure-function relationships within the glomerular array, integration and blend specificity, time coding and the effects of neuroactive substances and hormones on antennal lobe processing.

Summary: In the Japanese scarab beetle, Phyllopertha diversa , olfactory receptor neurones specific for the detection of so‐called general green leaf volatiles (GLV) display a high specificity and sensitivity. Three main types of green‐leaf‐volatile‐detecting receptor neurones specific to ( Z )‐3‐hexenyl acetate, ( E )‐2‐hexenal and ( Z )‐3‐hexenol, respectively, were identified. Each type responded at a very low stimulus concentration to the key stimulus, and required at least a thousand‐fold increase in concentration to respond to any of the other GLVs tested. Flower‐odour‐and pheromone‐detecting receptor neurones were also identified. Olfactory sensilla housing plant‐odour‐ or pheromone‐detecting receptor neurones displayed clear morphological differences, and were also separated into different antennal regions.

Recordings from antennal olfactory receptor neurones in young adult Schistocerca gregaria Forskål (Orthoptera: Acrididae) showed that behaviourally important odours are detected by receptor neurones present in morphologically identifiable sensillum types. Both nymph‐ and adult‐produced aggregation pheromones activate receptor neurones housed in sensilla basiconica. The receptor neurones in this sensillum type in solitary‐reared locusts display a higher sensitivity to aggregation pheromones and to some other behaviourally relevant odours than the same type of neurones in gregarious locusts. Receptor neurones present in sensilla coeloconica respond to green leaf odours, organic acids, and nymphal odours but are inhibited by mature adult‐produced aggregation pheromones. Receptor neurones housed in sensilla trichodea respond to a possible sex pheromone. No phase differences were found in the response of coeloconic‐ or trichoid‐associated receptor neurones.