The third antennal segment (= funiculus) of wild-type Drosophila melanogaster shows a sexually dimorphic distribution of sensilla: Males possess about 20% less of large basiconic sensilla, but approx 30% more trichoid sensilla than the female. The funiculus of the mutant lozenge3 is much reduced in size. Moreover, basiconic sensilla are completely lacking, and the number and density of trichoid sensilla are reduced. In contrast, the number and density of coeloconic sensilla are increased. The loss of sensilla in lozenge3 leads to a corresponding loss of sensory fibers in the antennal nerve. The antennal commissure of the wild type consists essentially of afferents from the funiculus which extend into the contralateral half of the brain. In the antennal commissure of lozenge3, more than twice the number of fibers lacking in the antennal nerve have disappeared which suggests that most afferents establish purely ipsilateral terminals. A highly specific change in the brain of lozenge3 is the loss of a particular subunit of the antennal center, the glomerulus V. This has previously been shown to be a major target of fibers from basiconic sensilla. Mosaic flies exhibiting a lozenge3 antenna demonstrate that the elimination of glomerulus V is causally related to the change in the sensilla pattern. This implies that the development and/or survival of particular target regions in the antennal center depends on sensory input. Furthermore, it shows that glomerulus V is specifically involved in the processing of information from basiconic sensilla.