The apple maggot, or "railroad worm," is one of the most serious pests of apples in the fruit growing areas of the Northeast. All apple varieties are subject to apple maggot attack, but summer varieties and early fall varieties are especially subject to injury. The insect also attacks certain varieties of European plums.

Description:

The adult apple maggot is a black-bodied fly slightly smaller than the house fly. The female is larger than the male and has four white bands across the abdomen, while the male has only three abdominal bands. The wings of the fly are crossed by four dark bands.

Damage:

Signs of the infestation on the fruit are minute egg punctures in the skin and pitted areas on the surface. In late-season varieties the injury usually appears as corky spots or streaks in the flesh. In the varieties ripening during July, August and September open tunnels may occur. Rot-producing organisms follow the maggots, causing rapid decay of infested fruit.

Life Cycle:

The adult flies emerge from their overwintering puparia (cocoon-like structures) in the ground during the latter half of June and continue to emerge through the middle of August. After emergence, the flies feed, mate, and, after 7-10 days, begin to lay eggs. During this time they may be seen resting on the leaves or fruit of apples and other host plants, lapping up drops of honeydew or moisture with their fleshy mouthparts. The female has a sharp ovipositor with which she punctures the skin of the apple and inserts her minute whitish egg into the pulp of the fruit. A large number of eggs may be deposited in a single fruit, and fruits of late varieties become dimpled and pitted as a result. The eggs hatch in 4 to 6 days, young maggots beginning at once to tunnel through the fruit, leaving brown trails. Severely infested fruits often fall to the ground early. The numerous trails in the fruit reduce the inside of the apple to a brownish, pulpy mass and render it unfit for consumption. The full grown maggot, which is about 10 mm (1/8 inch) long, leaves the fallen fruit and burrows into the soil to a depth of 25-50 mm (1 to 2 inches). Here it forms a puparium, the stage in which it overwinters.

Control:

For backyard apple trees, red sphere sticky traps can control the apple maggot fly without the use of pesticides. A small amount of damage may occur, but not enough to warrant spraying. In mid- to late June, place spheres within the canopy at about head-height. Set out one trap for every 150 apples (1 trap per dwarf tree, 2-4 per semi-dwarf or 4-8 per full size standard tree). Traps may be removed at the end of August. For both backyard apple trees and orchards, picking up and destroying fallen apples at weekly intervals from early August through harvest destroys the larvae within the fruit and reduces the potential for maggot injury the following year. This is most practical where trees are isolated and wild or abandoned trees are not nearby. For an overview of home apple tree management, a list of insect trap suppliers and sources of disease-resistant trees, see "Home Tree and Small Fruit Pest Management Guide," or visit the URI Apple IPM website at http://www.uri.edu/research/IPM

Adapted from the Cornell Cooperative Extension, 1999.