Apple Maggot

Order: Diptera
Family: Tephritidae
Species: Rhagoletis pomenella

Identification: Apple maggot larvae are relatively nondescript maggots; they are cream-colored maggot-shaped larvae that grow up to ¼” when mature. Other worms inside apples can be confused with apple maggot, however caterpillars like codling moth feed in the apple’s core while apple maggot feeds on the fruit flesh. Copious amounts of frass can be found when apples are infested with caterpillars. Apple maggot adults are about ¼” long and are black-bodied. The pattern on the wing is banded with black markings. Using your imagination, the pattern mimics the silhouette of a pseudoscorpion or crab spider for defense. The head is light brown with reddish eyes. Females have four white bands across the abdomen while the males only have three. It is easy to identify these flies to family but very difficult to identify the species. There are some commonly occurring fruit flies that look similar, if not exactly like, the apple maggot such as the snowberry maggot, walnut husk fly and cherry fruit fly.

Life History: There is one generation of apple maggot per year in the Northwest. Apple maggots overwinter in the soil in the puparium stage, the transitional stage between larva and adult flies. Adults will emerge from the soil in late June to early July. This emergence will last through September. Peak flight of the adults usually occurs around the end of July or early August. The female inserts an egg underneath the outer skin of the apple. Females can lay, on average, 300 eggs per 30 days of adult life. Apple maggots prefer apples (Malus) as hosts but apple maggots have been found on hawthorn (Crataegus) and other fruit trees such as plum and cherry (Prunus). Pending on temperature, the egg will hatch shortly and the maggot larvae will begin feeding. The larval stage can feed anywhere from two weeks to a month inside the fruit. Rarely will the larvae exit the fruit while it is still on the tree. The fruit undergoes rapid decay from the larval damage and will fall from the tree. After which, larvae exit the fruit and pupate in the soil for the duration of winter and spring. A small proportion of the population will not emerge as adults for an additional year, thus making apple maggot control at least a two year process.

Damage: Ovipositional (egg-laying) wounds are seen as small dimples or pin-pricks on the skin of the apple. This can cause deformation of the developing fruit or cause rapid decay of the area on softer varieties. The developing maggots tunnel throughout the fruit feeding on the ripening tissue. As the infestation progresses, brown squiggly lines appear on the fruit as the apple undergoes rapid ripening and decay. Infested fruit is unmarketable and unappetizing for most people. Early maturing and thin-skinned varieties of apples are more susceptible due to their timing and tendency of softer flesh.

Monitoring & Management: The Washington State Department of Agriculture monitors apple maggot populations every year. For the past few years, they have detected apple maggot in Whatcom County. Its presence makes it difficult for our local commercial apple growers to export fruit and threatens local orchard livelihoods. Whatcom County has a Horticultural Pest and Disease Board that was developed to protect local agriculture from the introduction and spread of serious pests, such as apple maggot. The pest board has the ability to work with local communities to keep pests at bay from neighboring agriculture. By state law, landowners are expected to manage these pests of concern, or in some way reduce the threat by removing the pests from their property. For landowners with apple maggot, host removal is the preferred method for control.

For apple lovers, chemical control is unfortunately a necessity once apple maggot is present in an orchard. Chemical treatments can be timed to target the flying adults. Local garden centers and farm supplies offer apple maggot traps and lures for monitoring adult flies. Insecticide treatments are timed when the first flies are trapped. Visit Hortsense (http://pep.wsu.edu/hortsense/) for the latest recommendations to manage apple maggots. Sanitation of orchards can reduce populations and help deter apple maggot. Clean up apples around the base of the tree as they fall. Early varieties should be cleaned up two or three times a week while later varieties should be collected at least once a week. To attempt to break the cycle of infestation by apple maggot, remove all apples from the tree before August for at least two years in a row. Destroy or dispose of apple in a manner to avoid re-infestation. Composting infected apples may not kill all the larvae developing. WSDA recommends to bury the apples at least 18 inches below ground in a pit. Another suggestion is to place apples in a sealed, heavy-duty garbage bag and set out on blacktop for a few sunny days then the apples can be composted or placed in your garbage. Apples can also be fed to livestock as long as they are placed in a feeding trough and not bare ground. To insure apple maggot is not a problem for you or neighboring apple enthusiasts, remove any neglected or unwanted trees. With a little effort, we can go on enjoying some of the best tasting apples in the state.

For more information about apple maggot management see: http://cru.cahe.wsu.edu/CEPublications/eb1928/EB1928.pdf or http://whatcom.wsu.edu/ag/homehort/pest/maggot.htm

For a detailed description about the Whatcom County Pest and Disease Board, visit: http://www.co.whatcom.wa.us/boards/horticulture.jsp or http://www.mrsc.org/mc/whatcom/whatco02/Whatco0228.html