I don't think they are solely to blame but they are the biggest cause of moose mortality. Let's say they kill x% of the moose and both species can have stable populations at that level. Then you add in brainworm at 1/5x and something else at 1/5 x and wolves increase 20% and that tips it over the edge and the moose population crashes. Do you blame the feather that broke the camels back or the main cause of moose mortality? You will have to decide that.