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ISSUE 13   JULY 29, 1999



    Although their preferred hosts are apple and crabapple, apple maggots can feed on hawthorn, pear,
and some stone fruits. Apple maggots disfigure apples and can significantly reduce their shelf life. Fruits
may be deformed by small brown spots and "dimples" caused at points of egg deposition. Larval feeding
can cause brown streaks in the fruit’s flesh which allow the entrance of decay organisms. Although
infested fruit is edible, some people find it undesirable to eat. Removing apples that are dropping now,
and throughout the remainder of the season, may reduce problems caused by apple maggots in future
years. Trapping and chemical applications can also reduce the impact that this insect may have on fruit.

    Apple maggots overwinter harsh North Dakota winters as pupae in the soil, often beneath previously
infested trees. Adult apple maggot flies begin emerging in late spring, or early summer, in North Dakota.
They are similar in size and appearance to small houseflies, but can be distinguished from houseflies by
the black banding on their wings. The adults must feed and mate, generally for about a week, before
they begin laying eggs directly beneath the skin of apples. Each female can produce more than 300 eggs;
therefore, a few apple maggot adults can cause considerable damage to the fruit on an apple tree. After
a few days, the eggs will hatch and the larvae will begin feeding. Apple maggot larvae can be distinguished
from other common fruit insect larvae by the absence of an enlarged, colored head. Other insects, such as
the plum curculio, have distinctive heads. Larvae will generally feed for up to a month and remain in the
apple until it drops to the ground.

    Once apples reach the ground, the larvae exit the apple and enter the soil to pupate. Since apples
may continue to fall throughout the remainder of the season, sanitation must be completed on a continual
basis (at least twice a week) to reduce apple maggot problems in future years. The effectiveness of
sanitation efforts will depend on the proximity of other hosts, your commitment to cleaning up dropped
apples, and your apple tree-owning neighbor’s (especially within 300 ft.) commitment to sanitation.

    Traps and chemical treatments are important tools which are often used to reduce apple maggot impact
on fruit. Dark-red spheres, which simulate apples, are covered with a sticky material, and hung among
the foliage (without touching leaves or fruit) in apple trees, to capture adult apple maggot flies. Apple
volatile lures may be used to increase the attractiveness of the traps to the egg-laying adults. These traps
should be monitored daily beginning in June until the first fly is caught, then weekly to assess the effectiveness
of treatments. If chemical treatments are used, they should begin as soon as the first adult is captured on
a trap without a volatile lure or five adults are captured on a trap with the lure. Carbaryl, diazinon, malathion,
and other chemicals can be used to protect against apple maggots. Mass trapping, with six, or more, red,
spherical traps, has been reported to be sufficient in reducing maggot numbers to acceptable levels, without
using insecticides.

Marcus Jackson
NDSU Extension Forester

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