Sensory axon extension and guidance is unaffected by expression of comm^{HP.dsRNA.Scer\UAS} under the control of Scer\GAL4^elav.PLu. Embryos expressing comm^{HP.dsRNA.Scer\UAS} under the control of Scer\GAL4^unspecified in the midline have thinner commissures than normal and in some cases the commissures and sections of the longitudinal tract fail to form. Growth cones stall at the midline. Embryos expressing comm^{HP.dsRNA.Scer\UAS} under the control of Scer\GAL4^elav.PLu have thinner longitudinal tracts than normal, show stalling of axons around the commissures and occasionally have thinner commissures than normal. Expression of comm^{HP.dsRNA.Scer\UAS} under the control of Scer\GAL4^eg-Mz360 results in axon bundles failing to cross the midline in some segments, and in some cases the axon bundles appear to turn away from the midline. When one copy of comm^{HP.dsRNA.Scer\UAS} is present, 13% of hemisegments show midline crossing errors and these errors are limited to the more medial neurons. When two copies of comm^{HP.dsRNA.Scer\UAS} are present, 61% of hemisegments show midline crossing errors and more lateral neurons now show these errors. These errors appear to be overcome by late stage 15. Expression of comm^{HP.dsRNA.Scer\UAS} under the control of Scer\GAL4^15J2 or Scer\GAL4^MZ465 does not result in guidance errors in the ipsilateral neurons in which comm^{HP.dsRNA.Scer\UAS} is expressed using these Scer\GAL4 drivers.