A rash of high-speed chases in downtown L.A. is threatening the livelihood of local fruit vendor Dave Rostand. 'Every week, as many as 10 high-speed auto chases, either comical or dramatic in nature, come roaring past my corner, sending my cardboard-box-mounted pyramid of oranges flying in all directions,' Rostand, who estimates he has had to rebuild his fruit stand 50 times, told members of the Los Angeles Chamber of Commerce Monday. 'If these chases are not curtailed, I will have no choice but to declare bankruptcy and take up work as a sheet-glass courier.' 