Apple Maggots - the newest worm in your apples and pears

Apple Maggot

Apple Maggots are just emerging from the soil under apple trees in the Fraser Valley. The fly in this picture was caught on my trap in North Langley on July 9, 2020. If you are trapping, please let me know the date that you catch your first fly.

Apple maggots are known as fruit flies. The Apple Maggot is closely related to these insects common in BC: Western Cherry Fruit Fly, Black Cherry Fruit Fly, Walnut Husk Fly and the Snowberry Fruit Fly. Apple Maggots are not related to the Spotted Wing Drosophila.

This pest moved into BC from Washington State in 2006 and quickly spread throughout the lower mainland. The Okanagan Valley is the only commercial apple growing zone in North America free of this pest (we hope) and everyone involved with this industry is trying to keep it that way. See the link at the end of this article to the FAO press release about Apple Maggots in the Okanagan.

Apple maggots spend the winter in the soil under the apple trees in the pupal stage. As the soil warms in late June and early July, the adults begin to emerge. A week to 10 days after emerging the flies mate and egg laying starts. Emergence and egg laying continues through October.

The table below is from two years of trapping Apple Maggots by the BC Ministry of Agriculture in several non commercial (unsprayed) locations in the Fraser Valley.

Apple Maggot Emergence Data for Fraser Valley- From Tracy Hueppelsheuser Presentation
Apple Maggot Emergence Data for Fraser Valley - Credit to Tracy Hueppelsheuser, BC Ministry of Agriculture

The adults feed on honeydew produced by aphids or other insects, and after 7 to 10 days mate and lay eggs. Each female can lay a total of up to 500 eggs over its life span of 2-4 weeks.

The female makes a tiny puncture in the fruit and inserts one egg just below the skin. This initial fruit damage is easily overlooked, but eventually leads to fruit dimpling. Eggs hatch in 3 to 7 days, and larvae start tunneling through the fruit. As they tunnel through the apple, they leave winding brown trails that are best seen when the fruit is cut open (see images above). When fruit are cut open the maggots are difficult to find as they are small and their color is similar to the apple flesh. The first indication that a backyard apple tree is infested with apple maggot is usually when the gardener discovers these brown trails in fruit at harvest.

Larva development is completed in 15 to 50 days depending on temperature, at which point the fruit often drops to the ground. The damage the maggot inflicts caused the production of ethylene (ripening gas). Ethylene triggers the collapse of a layer of cells (abscission layer) located at the point where the fruit are attached to the fruit spur. This layer of cells usually collapse when the fruit are ripe and start producing ethylene gas naturally. After the fruit fall the larvae leave the fruit and burrow into the soil to pupate ready for next year. There is usually only one generation per year.

Apple Maggot Prevention: Prevention for home gardeners and home orchardists is that same as for Codling Moths. Please see this post.

Summer Apple Maggot Population Control: to reduce the number of Apple Maggot that pupate under your trees gather up any fruit that fall destroy them. One effective way to do this is to put them in a clear plastic bag in the sunshine.

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