How do rosy apple aphids damage developing apples?

The rosy apple aphid (Dysaphis plantaginea) damages developing apples by feeding on the fruit, which results in significant deformation of the crop, often referred to as "aphis apples".1

In addition to damaging the fruit, the feeding activity of these insects causes the leaves of the apple tree to curl around them. This curling behavior is particularly problematic because it provides the aphids with protection from insecticide sprays, making them more difficult to control. While they are a serious pest, they can be managed by natural enemies such as lady beetles, lacewings, syrphid flies, and parasitic wasps, or through the application of insecticides when necessary.1