Apple Maggot Invades the Pacific Northwest
Since first detected in 1979 in Portland, Oregon, the apple maggot has spread and infested apples in many parts of the Pacific Northwest. Homeowners may want to rethink growing apples and other fruit trees. Many spray products labeled for homeowner use on fruit trees have been canceled. While apple maggot can render the fruit on your apple tree inedible, pockets of unsprayed “backyard” trees pose a serious threat to the commercial apple industry in the Northwest.
Commercial growers face added costs for insecticides to protect their fruit from apple maggot. They also risk restrictions from over- seas markets that strictly enforce pest quar- antines. To date, the apple maggot has not established itself in the major apple produc- tion areas of central Washington. Regulatory agencies are working to maintain these areas as apple-maggot-free zones. Homeowner cooperation and assistance in controlling this pest are critical to protecting the Northwest tree fruit industry.
The apple maggot, Rhagoletis pomonella, is an insect native to eastern North America. Apple maggot fed on hawthorn fruit until European colonists introduced the domestic apple to North America. Now apple maggot has spread throughout most of North America as a key apple pest. While hawthorn and apple trees are the primary hosts, apple maggot has been reported in crab apples, plums, apricots, pears, cherries, and wild rose hips.
Life Cycle and Damage to Apples
Apple maggot adults are known as fruit flies (fig. 1). Female flies lay their eggs singly in apples and other fruits. This egg-laying activity begins in July and continues though early October. When laying each egg, the female makes a tiny puncture in the fruit and inserts the egg just below the skin. This initial fruit damage is easily overlooked, but eventually leads to fruit dimpling (fig. 2).
Apple maggot eggs hatch in 3 to 7 days as small (less than 1/16 inch), cylindrical, cream- colored larvae known as maggots. Maggots lack legs and visible head capsules, but have dark mouth hooks that protrude from tapered heads (fig. 3). As apple maggots tunnel through the apple flesh, they leave characteristic winding brown trails (fig. 4) that are best seen when the fruit is cut open (fig. 5). The first indication that a backyard apple tree is infested with apple maggot occurs when the homeowner discovers these brown trails in fruit at harvest.
The apple maggot has one generation per year. Mature larvae exit the fruit, drop to the ground and overwinter as pupae in the soil under the infested tree. In early summer, apple maggot flies emerge from the soil and forage in the host tree canopy. There they feed on honeydew, bird droppings, and other sticky, sugary substances. An apple maggot fly mea- sures 1/4 inch long. It has a black body, dark red eyes, black and creamy-white striped abdomen and a white spot on the thorax between the pair of transparent wings (fig. 1). The black banding pattern on the wings is a key character to distinguish apple maggot from other fruit flies. The one exception is a snowberry maggot that feeds on snowberry bushes, but not on apples. Experts rely on microscopic examination to distinguish the apple maggot fly from the adult fly of the snowberry maggot.
Apple Maggot Quarantine Program
The apple maggot fly has expanded its range to areas in Washington State, Califor- nia, Idaho, Oregon, Utah, and Colorado. Apple maggot is established in 17 western Washington counties and in Kittitas, Klickitat, Skamania, and Spokane counties in central and eastern Washington. To prevent apple maggots from spreading to other counties, local authorities rely on early detection and immediate eradication programs. Washington State Department of Agriculture (WSDA) and local Horticultural Pest and Disease Boards monitor apple maggots throughout Washington State.