Spinosad (#T177), a quick acting broad spectrum natural insecticide spray derived from the metabolites of a common soil bacterium, and BioNeem (#T172), a natural insecticide derived from the Neem tree, are both effective against codling moth, plum curculio, and currant worm caterpillars before they enter the fruit.
Use Spinosad for heavier infestations, and follow label instructions on timing to avoid damage to beneficial insects, up to 6 sprays per year. Use BioNeem when you prefer a more gentle approach. The first spray is applied 2-4 weeks after bloom, or when you start seeing pin hole scars in the fruit (from the little caterpillars chewing their way into the fruit).
Applying spray in August is helpful in controlling second or third generations of these pests. Start looking for the scars a week or so after catching increased numbers of adults in your monitoring traps, when you start seeing new scars it is time to spray.