In most Western climates, homegrown apples are plagued by codling moth larvae-3/4- inch-long, pinkish white worms. On the outside of the apple the only sign of their presence is a small puncture wound with a mound of brown excrement around it. On the inside, they bore into the core and damage the pulp and seeds.
You can still eat infested apples-if you don't mind cutting out the worm first. But grocery stores have so accustomed us to fruit free of insect damage and blemishes ...