Apple Maggot
Fruit damaged by apple maggots eventually becomes soft and rotten, and cannot be eaten.
Apple Maggot Life Cycle and Damage
Female apple maggot flies deposit eggs singly just below the skin of an apple or other host fruit. When the female lays an egg, a small but visible puncture is made in the fruit which can lead to "dimpling." Eggs are elongate (l/16 inch)* curved, smooth, and white. Depending on temperatures, the eggs hatch after a 3-7 day
incubation period.
The tiny cream-colored larvae (maggots) feed in the fruit, passing through three growth stages.
Maggots are about 3/8 inches long. The damage caused by the maggot resembles a series of brownish, irregular tunnels called railroading. The tunnels are enlarged by bacterial decay that often follows apple maggot damage. Damaged fruit eventually becomes soft and rotten and cannot be used.
After about 20-30 days in the fruit, the maggots drop to the ground where they bury themselves in the soil. There they change to the pupal stage and spend the rest of the winter. They emerge as adults from July through September. The adults must feed for a period of 7-10 days in order to reach sexual maturity. After this period, they are attracted to fruit, where they mate and the females lay eggs. There is one generation per year. The apple maggot fly is about l/4-3/8 inches long. It has a black abdomen. Females have four white bands on the abdomen. The smaller
males have three bands. The wings are clear but are marked with black bands. The apple maggot is closely related to the walnut husk fly, cherry fruit fly, and other picture-wing flies, including the snowberry maggot, an extremely close "look-alike.' Because of their close resemblance to these insects, entomologists must dissect them to confirm their identity.
Control
Since apple maggot renders apples virtually inedible and no completely effective cultural or biological control techniques exist as yet, chemical control becomes essential if this pest has been detected in your fruit. The names of currently recommended spray products can be obtained from your local County Extension office. Since the adult flies are emerging over a long period of time, it is important that applications begin about
mid-July and continue at 7-10 day intervals up to the preharvest interval man- dated by the label of the
insecticide you choose.
Apple Maggot Quarantine
Apples affected by apple maggots are completely unuseable and unsaleable. The apple maggot, Rhagoletis pomenella, is a native insect of North America and has historically been a pest
of apples in the northeastern United States and eastern Canada. In 1979, the apple maggot was first
discovered in the Pacific Northwest in the Portland, Oregon area. Since then, apple maggot adults have been
found in most western Washington counties. The Columbia River Gorge counties of Skamania and Klickitat
are also infested. In eastern Washington, flies have been caught within a sizable area inside Spokane county.
To date, neither apple maggot flies, maggots, nor fruit damaged by them have been detected in commercial
orchards in Washington state.
The Washington State Department of Agriculture has developed an extensive statewide survey for the apple
maggot. Traps designed to catch apple maggot flies, and a few closely related flies, are set up throughout
much of the state. The traps are set up in June and are monitored through September. This program is
expected to continue for several years and will monitor the distribution of the apple maggot. Food plants that
host the apple maggot include several members of the rose family. Apples are the main host of the apple
maggot, but they are frequently found in hawthorn and crab apple as well. Early cultivars (varieties) of apples
are particularly susceptible to early damage by the maggot. Apple maggot has also been located in plum,
cherry, apricot, pear, wild rose, pyracantha, and cotoneaster. Apple maggot may be able to adapt to other host
plants in the future.
Highway Quarantine Signs
Questions are frequently asked as to what the apple maggot signs along Washington freeways and highways
actually mean. The following should clarify.
In Western Washington?
The highway signs in western Washington that say "Apple Maggot Quarantine Area/Please do not
transport home-grown tree fruit" are intended to draw attention to the existence of the quarantine and to
the fact that backyard or noncommercial tree fruit grown in much of western Washington may not be taken
out of western Washington or across county lines.
At Canadian and Oregon Borders, Cascade Mountain Passes?
These are all points at which you are leaving the western Washington quarantine area. The signs indicate that
it is illegal for you to carry backyard or noncommercial treefruit north into Canada, south into Oregon, or
east across the Cascade Mountains.
For more information contact your local WSU Extension office.
Prepared by Elizabeth Beers, Ph.D., Extension Research Entomologist, WSU Wenatchee; Arthur L.
Antonelli, Extension Entomologist, Ph.D.,WSU Puyallup; and Eric LaGasa, M.S., Chief Entomologist,
WSDA. Olympia, Washington. Reviewed by Mary Robson, Horiculture Agent, 1996.
