Not sure about apples, but I know peach and cherry trees can get borers. I just treated my trees with a product that's supposed to kill eggs/larvae in the ground, as well as be taken up by the roots to get the ones that are already under the bark. Not really sure it will work. The only "proven" treatment for borers is illegal now (dursban). The new products don't have a long enough "track record" to be labelled "effective." My cherry has evidence of borers, but the peach is free of them from what I can see - I treated both just in case...

Cherries in Utah used to get a little white worm in them if you didn't spray for it - some kind of fruit fly maggot I think. Not sure if that's a problem here or not, I would assume it is(?) As my dad used to say, "what's a little more protein" :P bleh... You can spray for these guys when the cherries are green. You spray the ground, as the adult flies will be emerging from the ground under the cherry tree, and you can spray the tree as well to get the adults that travel from other trees/yards.