Apple Maggot

Apple maggot is a native pest of the eastern United States and Canada. In 1979 it was discovered in Oregon and has since moved into California, Washington, and other Western states. Hawthorn and apples are favored host plants, but cherries, pears, and other fruits have been attacked.

Adult flies are somewhat smaller than houseflies and have clear wings with characteristic black bands, a pronounced white spot on the back of the thorax, and a black abdomen with light-colored crossbands. Female flies have four crossbands on the abdomen, and males have three. The apple maggot is closely related to the walnut husk fly and cherry fruit fly. It can be distinguished from these other pests by the banding on its wings. However, it is difficult to distinguish apple maggot from snowberry maggot, a close look-alike that occurs throughout California but that does not attack apples and pears. Larvae are cream-colored maggots with a blunt posterior and a tapered front end that contains two black mouth hooks.

Female apple maggot adults deposit eggs singly under the apple skin. Damage is caused when larvae burrow and feed on apple flesh. Browning of the trails occurs as the apple responds to this injury and bacteria associated with maggots cause fruits to rot internally.

In areas where apple maggot is established, the pest is managed with sprays of organophosphate insecticides targeted to the first emerging adult flies. Not all orchards require treatment. Use sticky traps for detection and treatment timing. If apple maggots are found in counties where it is not yet established, notify the county agricultural commissioner.

Because the apple maggot feeds within fruit, biological control agents have not been very effective.

Baited sprays such as GF-120 are organically acceptable. Mass trapping with dark-colored, plastic sticky spheres (placed 1–2 per tree) has been used by organic growers in the eastern U.S. to greatly reduce damage. Replace traps when sticky material is no longer effective.

Emergence and dispersal of adult flies must be carefully monitored to effectively time treatments. Sticky traps, including yellow rectangles and red spheres, are both used in other areas to monitor adults and time treatments. Unfortunately, only provisional economic thresholds are available for apple maggots, even in areas where it has long been a pest. You can detect the first emergence of adults by hanging yellow sticky traps in abandoned orchards or unsprayed apple trees in infested areas. To detect the beginning of egg laying, hang red sticky spheres in apple trees, then treat as soon as the first fly is found. In Oregon, where some orchards are now being treated regularly for apple maggots, the first maggot spray is applied 7 to 10 days after the first fly has emerged. Later sprays follow at 10- to 14-day intervals as long as adults are active and are being caught in traps.