Once you banish the black ones the white ones will be back, at least that is the way it works for me. Other than the lanterns, the shotguns and the flares seem useless too.White wraiths stopped visiting my city once I completed one of the tasks associated with banishing some number of black ones. Now I constantly have bunch of black creatures around my city. Is this expected? Sort of disappointing to see lanterns flying directly to trash bin.