In a bowl, combine pears and lemon juice and toss gently and set aside. In another bowl, combine sugar, 1/3 cup flour and ginger; then, add sugar mixture and corn syrup to the pears. Spoon mixture into pie shell. In a small bowl, combine 1/3 cup of flour and brown sugar; add butter and mix until crumbs form. Sprinkle on pear mixture and bake in a preheated oven at 450 degrees for 15 minutes. Reduce heat to 350 degrees and bake 30 minutes longer.