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Orchard Pest Management Online

 

Apple maggot

Rhagoletis pomonella (Walsh)
(Diptera: Tephritidae)

-- Jay F. Brunner and Michael W. Klaus
  (originally published 1993)

Apple maggot adult (H. Riedl)


Apple maggot is a native North American pest whose original host was hawthorn. It was first reported as a pest of apple in the 1860s and has become a key pest of commercial apples throughout eastern Canada and the northeastern United States.

The first confirmed apple maggot infestations in the Northwest were in Oregon in 1979. Since then, trapping programs have located maggots in western Washington and western Oregon, as well as on both sides of the Columbia River Gorge and in Spokane, in eastern Washington. It has also been found in Idaho, Utah, Colorado and California. The pest apparently can survive in a wide range of conditions, from the cool, coastal climate of western Oregon and Washington, to the hot, dry climate of The Dalles, Oregon, or the mountain conditions of Utah.

It is likely the maggot was introduced to the western United States by people transporting infested fruit from the eastern states. It probably had been in the West for many years before being detected. Since 1980, detection of apple maggot at new sites is attributed more to intense monitoring than a spread of apple maggot infestations.

In the early 1980s, states in the Pacific Northwest launched programs to control and contain apple maggot. The emphasis was on preventing the pest becoming established in the major apple growing regions of eastern Washington. Host trees, usually apple or hawthorn, were sprayed or removed to reduce the number of apple maggot flies and potential breeding sites.

The control/containment program ended in 1985 when financial resources became limited and the apple maggot was found in native hawthorn along streams, preventing control by insecticides. While the distribution of apple maggot has spread to a few more counties in western Washington since 1985, infestations in eastern Washington are still restricted to the Spokane area and along the Columbia River Gorge.

If apple maggot were to become established in major fruit growing regions of the Pacific Northwest, it could have a serious economic impact on the industry. Direct costs to the fruit grower for additional insecticide applications would account for only a small portion of the potential losses. Export markets would be lost and additional fruit would be channeled to the domestic market. Sprays to control apple maggot would have to be applied late in the growing season when most apple growers apply few insecticides. Such additional sprays may disrupt the IPM systems already in place in commercial orchards.

 
Hosts

Apple maggot is very adaptable and can infest many different plants including apple, hawthorn, plum, apricot, pear, sweet cherry, sour cherry, wild rose, Cotoneaster sp. and Pyracantha sp. However, in Washington it has been found only on apple, crab apple and hawthorn. It most often attacks early maturing, sweet varieties of apples.

 
Life stages

Egg: The egg is whitish, small, smooth, elongated and slightly curved. Eggs are rarely seen because they are laid beneath skin of the host fruit.

Apple maggot larva in apple (R. Kriner)


Larva: The apple maggot larva is a typical fly larva. It is cylindrical, tapering from a blunt posterior to a pointed head, and has no legs. The mature larva is creamy white except for two dark mouth hooks and is 1/4 to 3/8 inch (6 to 9 mm) long The larva tunnels through apple flesh and can be distinguished from other insect larvae found in apples by its lack of a distinct head capsule.
Pupa: The pupa looks like a large, dark brown grain of wheat. It is usually found in the top 2 inches (5 cm) of soil under infested trees.
Adult: The apple maggot fly is about the size of a common housefly. Its body is black, its eyes are dark red, and the thorax and abdomen have distinctive white or cream bands. The male has a blunt abdomen with three white lines, while the female's more pointed abdomen has four white stripes. A distinct banding pattern on its wings distinguishes it from most other Rhagoletis species except the snowberry maggot, which is found throughout the western United States.



 
Life history


Apple maggot spends the winter in the soil as a pupa. As the soil warms in the spring, it begins to develop. In late June or early July, adults begin to emerge . Flies continue to emerge from the soil throughout the summer and are active until October. Peak activity on various hosts depends on fruit maturity. Apple maggot activity peaks earliest on apple varieties maturing in midsummer, followed by native hawthorn and apple varieties maturing in early fall and finally by imported hawthorn and apple varieties maturing in late fall. In Washington, the apple maggot appears to move from one host to another as fruit matures. After emerging, the adult apple maggot feeds for 7 to 10 days until it becomes sexually mature. It eats mainly insect honeydew. Soon after mating, females lay eggs just under the skin of the host fruit. A female can lay between 300 and 500 eggs, which can hatch in as little as 3 to 7 days.

The larvae feed while tunneling through the fruit. It can take from 13 to more than 50 days for the larvae to develop. Temperatures and fruit hardness influence the rate of development. Full grown larvae leave the fruit, usually after it has fallen to the ground, and enter the soil to pupate.

Most apple maggot pupae stay in the soil for one winter, though some remain there for two years or more. A few flies may complete development the same year and produce a partial second generation. In Washington, this is suicidal, as there would not be enough time to complete larval development before the onset of winter.

 
Damage

External symptoms (dimpling) of apple maggot infestation in apple (J. Brunner)


Apple maggot feeds on fruit and if left unchecked can damage almost all the fruit on infested trees. Even small numbers of apple maggot can heavily damage apple crops. When eggs are deposited under the fruit skin the cells surrounding the puncture are damaged.

Apple maggot larva tunneling in fruit (J. Brunner)


As the apple grows it becomes dimpled and lumpy. This is more evident in apples attacked early in the season. Feeding by the larvae leaves brown trails in the apple flesh (Figure 92). When many larvae feed on a fruit, the flesh often turns mushy and the apple drops early. In hard, later maturing apples, internal breakdown may not be apparent until after the apple drops.

 
Monitoring

Apple maggot traps: left, yellow sticky panel: right, red sphere (J. Brunner)


Adults can be monitored with sticky traps. Use either a red sphere or a bright yellow panel with protein and ammonia extracts as a lure. Unlike pheromone traps, which attract moths from several yards, an apple maggot trap is effective only over short distances, generally the tree in which it is located. Because traps, particularly the yellow panel type, attract many kinds of insects, they need to be inspected and cleaned regularly.

Place traps within the fruiting canopy of the tree in the outer third, with panel traps positioned so that the broad surface is exposed to the foliage. Remove foliage from around the trap for 12 to 18 inches (30 to 45 cm) to make it more visible to the apple maggot flies. Place traps at intervals of 150 feet (45 meters) along the orchard border. Where the orchard borders a dusty road, place the traps one or two rows into the orchard. The commercially available pre-baited apple maggot trap should be changed every 7 days. Yellow panel traps using ammonium carbonate as a lure can be changed every 14 to 21 days, depending on how long the lure lasts and how contaminated the trap's surface becomes. Red sphere traps should be replaced or have the adhesive renewed every 4 weeks or more often if they lose their tackiness. Examine traps 2 or 3 times a week. Apple maggot trapping in the Northwest is complicated by the presence of the snowberry maggot, a fly that does not attack apple or other fruits but looks like the apple maggot. These two species cannot be distinguished in the field and must be examined under magnification by an expert. Remove any flies that look like the apple maggot, place in a vial with a solvent (Citra-Safe(r)) and take to an expert for identification. In Washington, this is usually done by the Washington State Department of Agriculture. In areas where there are high populations of snowberry maggot near orchards, the red sphere may be the trap of choice, since it is less attractive to this insect.

 
Biological control

The three most common parasitoids of apple maggot in the western United States are Biosteres melleus, Opius downesi, and a species of Pteromalus. They are all parasitic wasps that attack apple maggot larvae. The first two develop inside the host, while Pteromalus sp. is an ectoparasitoid and feeds on the outside of the larva. However, during three years' research in Washington no parasitism of apple maggot in apple was found, probably because the larvae burrow too deep in the fruit for the parasitoids to reach with their small ovipositors. Parasitism levels in hawthorn ranged from 0 to 60%. Biological control of apple maggot in commercial apple orchards holds little promise as a management tactic. However, parasitism in native habitats plays a role in suppressing of apple maggot populations.

 
Management

The management guidelines outlined here relate only to orchards in areas of Washington where apple maggot occurs. It has been detected in the Columbia River Gorge, Spokane and western Washington. The quarantine area is all of western Washington (except Whatcom, Skagit and Snohomish counties) and Skamania, Klickitat, Spokane and portions of Kittitas and Yakima counties in eastern Washington.

Control recommendations depend on how close the orchard is to an apple maggot detection. If the closest apple maggot detection is more than 1Ú4 mile from the orchard, no control is needed. If an apple maggot has been detected within 1Ú4 mile of the orchard, the orchard is considered threatened and the orchardist has two management options: no trapping or trapping.

No trapping: No monitoring is done and it is assumed that the apple maggot is in the orchard. As soon as the orchard is recognized as threatened, apply controls every 14 to 21 days until harvest. Have fruit inspected by the Washington State Department of Agriculture to certify it is free from apple maggot infestation, or place the fruit in cold storage for at least 40 days before shipping out of the quarantine area.

Trapping: The need for control is based on results of monitoring. Apply control treatments within 7 days of trapping an apple maggot fly in the orchard. If flies continue to be caught, repeat treatments in 14 to 21 days. If no more flies are caught within 14 to 21 days of the first capture, do not treat again until another fly is detected. Have fruit inspected by the Washington State Department of Agriculture to certify it is free of apple maggot infestation or place fruit in cold storage for at least 40 days before shipping out of the quarantine area.

Other recommendations: Remove apple maggot hosts within 1/4 to 1/2 mile of the orchard to reduce potential sources of infestation. Look particularly for wild or unsprayed apple trees, ornamental hawthorns and crab apples. Insecticides applied against the second generation of codling moth in mid-July or early August will give protection from apple maggot for 14 to 21 days.

 WSDA’s apple maggot control program

  • Established in 1980.
  • Administered in concert with the Apple Maggot Working Group, made up of representatives from Washington State Dept. of Agriculture (WSDA), Washington apple industry, tree fruit research community, and the federal government.
  • Consists of three components: A survey and regulatory component administered by WSDA; a control, suppression and eradication component administered by county pest boards; and an education component conducted by Washington State University through its cooperative extension offices.
  • Apple maggot trapping program conducted annually. Between 5,000 and 8,500 apple maggot traps placed in field each summer. Field activities determined by WSDA and Apple Maggot Working Group.
  • Trapping results forwarded to county pest boards for control, suppression, or eradication actions they consider appropriate.
  • Counties may be quarantined in whole or in part based on trap catches and other evidence of apple maggot activity detected.

Purpose of apple maggot quarantine

  • Facilitate the movement of commercial fruit to domestic and international markets by providing shippers with one of two types of WSDA documents certifying their fruit is apple-maggot free.
  • One certificate states no apple maggot flies were caught within a half-mile of the orchard shipping the fruit. The other certificate states flies were caught within a half-mile of the orchard, but WSDA inspection revealed no apple maggot larvae in the fruit.
  • For the latest on the apple maggot quarantine go to:  http://agr.wa.gov/PlantsInsects/InsectPests/AppleMaggot/default.htm

Success of apple maggot control

  • Apple maggots have never been found in commercially packed fruit in the state.

 

 

Orchard Pest Management, is copyrighted by the Washington State Fruit Commission. Soft cover copies are available for purchase.
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