Apple Maggots 2
The adults are black flies, 6mm long with yellow legs and a zigzag band across their wings. They over-winter in the soil as pupae, approximately 1 to 6 inches below the surface, and emerge the next spring in June to July, depending on the number of days with a temperature above 10 degrees Celsius. The flies then lay their eggs in developing apples. These eggs then hatch into white to cream maggots, which will tunnel through your apples, causing brown streaks.
To control apple maggots, one can root drench the tree with Diazinon early in the spring, this will kill any pupae in the soil before the adult flies are ready to emerge. This will not eliminate your problem though, because the flies are common in the area and will fly to your tree from elsewhere. It is also to be noted that Diazinon is harmful to birds. Spraying your trees with Sevin will prevent the flies from laying eggs in your apples, however it may be inconvenient, since you must re-spray the tree every ten days, beginning at fruit set. Do not spray your tree with Sevin seven days before harvest of the fruit. Sevin is also known to be harmful to birds. The most environmentally friendly control method is to hang traps in the trees. You may buy these traps at a garden center, or create them yourself by painting a Styrofoam ball red and covering it with Tangle-foot. The tangle foot should be removed and replaced once a week. Use one trap for a dwarf tree, and 4-8 traps for a large tree.