Flies in which W-FRT.Scer\UAS.cSa is expressed under the control of Scer\GAL4dimm-929 in the large ventral lateral neurons (l-LNvs) of the brain (Scer\FLP1Ecol\lexAop.cSa protein produced by expression of Ecol\lexAPdf.cSa.T:Hsim\VP16 has been used to generate W-FRT.Scer\UAS.cSa from its WScer\FRT.Scer\UAS.cSa progenitor in a subset of the Ecol\lexAPdf.cSa.T:Hsim\VP16 expressing cells) show a decrease in the number of l-LNvs compared to controls (from 10 to an average of 2-4 cells per hemisphere). Females have a consistent and significant decrease in daytime activity and a reciprocal increase in daytime sleep compared to controls. This phenotype is more obvious under constant light conditions and disappears under constant darkness conditions.