In addition to the general pests detailed here, there are other pests that can effect several different types of top fruits.
The larva of the codling moth can cause damage to Apples, Pears and to a lesser extent on Plums, Damsons and Quince. I have not seen it in Glasgow and I understand that it is rarely a problem in Scotland.
In other areas that have this pest, the adult moths lay their eggs on the fruits or leaves. The pest will show itself with a red-ringed entry hole in the fruits, where the larva has burrowed into them. For some four weeks, the larva will be burrowing into the fruits, causing extensive damage.
Where this pest is present, the usual recommendation is to hang codling moth pheromone traps during May to attract the male moths to their death.