Expression of RhoGAPp190^{dsRNA.GAP.Scer\UAS} under the control of Scer\GAL4^T80 or Scer\GAL4^ey.PB results in no obvious phenotype. Expression of RhoGAPp190^{dsRNA.GAP.Scer\UAS} under the control of Scer\GAL4^OK107 results in truncation or loss of dorsal branches of the adult mushroom body. There is no obvious defect in cell number or morphology of the calyx (where the dendrites are confined). The strength of the phenotype depends on the P{UAS-RhoGAPp190.GAP-dsRNA} insertion line used. In severe cases defects are seen in medial lobe fasciculation and truncated β lobes start to be seen. The severity pf the phenotype is enhanced by heterozygosity for Df(1)BK10 (which removes RhoGAPp190). Defects in the mushroom body neurons are not seen in animals expressing RhoGAPp190^{dsRNA.GAP.Scer\UAS} under the control of Scer\GAL4^OK107 at the end of the third larval instar. At 18 hours after puparium formation (APF), dorsal α' lobes are generally present, although pointed dorsal lobes and very thin processes punctated by dots at the tips of the lobes are seen, resembling aspects of axon retraction. By 36 hours APF most mushroom body neurons show medium or strong phenotypes (dorsal lobes are absent or retracting). Progressive reduction of the dorsal lobe can also be seen in adults carrying a P{UAS-RhoGAPp190.GAP-dsRNA} insertion that gives an intermediate phenotype.