Abstract: The paired antennal lobe is the primary olfactory center of insect brain, linked by antennal nerves to the antennae. The antennal lobe is mainly composed of olfactory receptor neurons, local interneurons, projection neurons and centrifugal neurons. Each of these categories of neurons is morphologically categorized into several types. The types associate with their functions and show species-specificity. The antennal lobe neurons are organized into neuropil with a large number of glomeruli, which house dense synaptic contacts and are arranged in one or two layers at the periphery of the AL. In a given antennal lobe, the number, size and position of glomeruli are constant and almost each glomerulus can be identified and named. However, the number, size and position of glomeruli show species-, sex- and caste-specificity. Such organization of the antennal lobe is associated with species- , sex- and caste-specific olfactory behavior of insects.

Key words: Insect, antennal lobe, olfaction, neurons, glomerulus, sexual dimorphism