The apple sawfly (Hoplocampa testudinea) are small wasp-like insects which first lay their eggs on the blossoms. The eggs then grow into maggots which tunnel just below the surface of the skin. It is this which causes the ribbon like scars on the outside of the fruit (see left). As the maggots grow, they then tunnel directly into the middle of the fruit, causing it to drop prematurely in early July. 

Preventative treatment consists of spraying the tree with derris (safe to humans and garden wildlife) when most of the apple blossom has fallen from the tree. 

If any fruit is attacked, remove it from the tree as soon as it is noticed and burn it - do not put it on the compost heap.