Female AM deposit single eggs under the skin of apples and, once hatched, larvae tunnel through apple flesh leaving brown trails. Egg-laying punctures are difficult to find unless the fruit is heavily attacked, as are most apples in an abandoned orchard.
- Adult AM is slightly smaller than the common house fly, with a bright white spot at the center of the dorsum (back), 4 black wing bands (3 of which look like letter F), and 3 or 4 white stripes on the abdomen. Mature larvae are 3/8 inch long, legless, white, peg-shaped, legless larvae.
- Apple maggot flies overwinter in the soil as pupae, and emerge as adult flies in June - July. They migrate to apple trees from unsprayed or abandoned trees and are known to migrate for at least half a mile. Once adults emerge from the pupae in the soil, they feed and mate. About 10-14 days after adult emergence females start depositing their eggs. Larvae feed for 3-4 weeks before leaving fruit and entering the soil.
- Activity usually ceases in late August or early September but can extend into October on late cultivars.
- There is one generation per year.
- AM adult flies can be monitored using sticky coated red spheres that mimic ripening apple fruits or with yellow sticky boards which act as a leaf mimic. Addition of a 5-component lure (commercially available) increases AM trap captures.
- Set out traps in late June at the rate of 1 trap per 3-5 acres, but not less than 3 traps per block. Place traps near the block periphery, 1 or 2 rows in from outermost row. Remove any leaves or fruit touching the traps.
- Apple varieties most susceptible to maggot attack are Wealthy, Cortland, Gravenstein, Red and Golden Delicious and early sweet or subacid varieties. However, AM will attack any variety.
- Recommended treatment threshold is an average of 2 AM per unbaited trap or 5 AM per baited trap.
- Trap captures for a week following insecticide treatment are ignored. Subsequent sprays can be applied once the threshold is reached again.