My bonsai tree has been fairly healthy since i bought it but suddenly its dropped all of its leaves. at first i was told that i might have watered it to much but then i noticed the moss died to so i pulled the tree out of the pot. there are little white bugs all over the roots. what could these pests be? and how do i get rid of the?

It could be a couple of different pests, use a mild mix of insecticide on the root ball and repot it after throughly washing the pot out in hot water to kill any eggs and put in fresh potting soil.