>- if it's possible to kill tree parasites with a zapper.
While I have not experienced this, I think that it is possible, depending on the type of parasite.
One consideration: Since the zapper appeards to work by breaking down the cell walls of lower organisms and since trees have cell walls, the trees may suffer some damage from zapping. I do not know for sure as the cell walls of trees are different. Humans and higher level animal organisms do not have cell walls which is why they are not negatively affected by zappers.