Posted: 31/08/2013 at 09:31
If you really need to get rid of them them Dovefromabove advice is the best, give the tree a good water spray. However the wasps are doing the same thing by eating the aphids and when they run out of food they will go away.
Please don't kill the wasps they are a very necessary part of the food chain. They only sting because they think they are being attacked and it's their way of fighting back.