Drosophila reproductive behavior will be studied using genetic tools. Questions on the control, by the various parts of the nervous system, of different features of courtship will be asked with genetic mosaics (following up our earlier studies). What parts of the dorsal brain must be male to allow the early steps of courtship to be performed? Are intermediate steps of courtship controlled by the brain, and if so, by the same parts? The later steps of courtship are controlled by male thoracic tissues: is the thoracic ganglion critically involved in such control? For female behaviors, which tissues must have a female genotype in order that a mosaic be receptive to courtship and copulation, or be able to carry out the post-copulation rejection behaviors? -- Several behavioral mutants affecting courtship have been characterized by behavioral observation and manipulation. Different mutants influence the early, middle, or late stages of courtship sequence. The causes of these reproductive defects will be analyzed, beginning with studies of mosaics: For instance, where in the fly must a small genetic duplication--carrying the normal allele of a gene involved in aberrant male-female and male-male interactions--be present in order that normal behavior occur? Some of the experiments here, on mutants and mosaics, will concern the possible genetic control of particular neural oscillators--those that drive motor output in the courtship lovesong. Also, we are dissecting the control of copulation--its basic duration, the relationship of that duration to sperm transfer, and the details of actions involved in its termination. -- The various mutants may affect the development or the functioning of the nervous system. In this light, we will analyze conditional alleles of certain of the mutants, to ask which stage of the life cycle is influenced by the genetic variants. -- We are asking several questions on triggers and inhibitions of courtship behaviors, influenced by putative pheromones. These experiments are related, not only to studies of normal males and females, but also very strongly to the investigations of behavioral mutants, and to the behavioral dissection of the brain in genetic mosaics.