Large round holes in immature apple, no frass present

All the other fruit on the apple tree appear fine with no signs of damage. Some very minor insect damage on some leaves and 3 scale found (and removed) but relatively few insects found on and around tree other than a couple of lacewings and a long thin white flying insect. A small grey bug also found on the bird netting. No cocoons, webbing etc present and tree limbs smooth with very few hiding places. Any idea what the culprit is and how to treat the tree to prevent damage to other fruit?