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The antennal flagellum of female Manduca sexta bears eight sensillum types: two trichoid, two basiconic, one auriculate, two coeloconic, and one styliform complex sensilla. The first type of trichoid sensillum averages 34 mum in length and is innervated by two sensory cells. The second type averages 26 mum in length and is innervated by either one or three sensory cells. The first type of basiconic sensillum averages 22 mum in length, while the second type averages 15 mum in length. Both types are innervated by three bipolar sensory cells. The auriculate sensillum averages 4 mum in length and is innervated by two bipolar sensory cells. The coeloconic type-A and type-B both average 2 mum in length. The former type is innervated by five bipolar sensory cells, while the latter type, by three bipolar sensory cells. The styliform complex sensillum occurs singly on each annulus and averages 38-40 mum in length. It is formed by several contiguous sensilla. Each unit is innervated by three bipolar sensory cells. A total of 2,216 sensilla were found on a single annulus (annulus 21) of the flagellum. Electrophysiological responses from type-A trichoid sensilla to a large panel of volatile odorants revealed three different subsets of olfactory receptor cells (ORCs). Two subsets responded strongly to only a narrow range of odorants, while the third responded strongly to a broad range of odorants. Anterograde labeling of ORCs from type-A trichoid sensilla revealed that their axons projected mainly to two large female glomeruli of the antennal lobe. (C) 2001 Wiley-Liss, Inc.