Are they the ones that live on primary stems and branches? Unfortunately, if they are, there are a few types of apple variety that they seem to like over others. When the tree is not in flower, I would use the spray provado on them but add a little washing up liquid to the solution so that it sticks to them.

The reason not to do it whilst in flower is provado kills bees but worse, they take it back to their nests before dying and it wipes the whole colony out. Spray late in the evening too.