Abstract
SUMMARY: Someyellowalleles which show full expression of the mutant phenotype have behavioural defects, including reduced locomotor activity and a low level of male competitive mating success. Otheryellowalleles produce pattern mosaics in which some cuticular structures areyellowand others wild type within the same individual. The pattern mosaic expression of these alleles extends to behaviour. Mosaicism in respect of the different pleiotropic effects reveals something about the possible mode of action of this locus on behaviour.