The Apple Maggot is a small fly that to the Northeastern United States and Canada, but has been dispersed to many other apple growing regions around the world. It can also feed on other hosts such pears, plums, and cherries. Adult flies lay eggs under the host fruit’s skin and as larvae emerge, they feed on the fruit, creating trails through the fruit. These wounds can lead to other infections and cause early rot and fruit decay. Early producing apple cultivars in the Pacific Northwestern United States are most susceptible to Apple Maggot damage.

Apple Maggot Life Cycle Stages

Apple Maggots overwinter as pupae in the soil, and adults emerge in late spring or early summer. Adults feed on honeydew produced by aphids, or other insects, until they are ready to lay eggs in the fruit. After larvae emerge and feed on the fruit, the fruit drops to the ground in fall and the larvae burrow into the soil to pupate. In most cases, there is only generation per year.

The period of adult emergence is key for insect prevention, both for placing traps and for using insecticides, if necessary. Researchers have created the Apple Maggot Emergence Growing Degree Day Model to better predict when the adults will emerge from the soil.

Calculating Growing Degree Day Units

The Apple Maggot Emergence Growing Degree Day model uses a lower threshold of 44.1F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

Using Mar. 1st as a default “biofix” date, or starting point for accumulation. The first adult emergence occurs at approximately 1457 GDD. This can be used an approximate target for beginning to place sticky traps in the orchard.

Source:

Jones, V. P., D. W. Davis, S. L. Smith, and D. B. Allred. 1989. Phenology of apple maggot, Rhagoletis pomonella (Diptera: Tephritidae) associated with cherry and hawthorn in Utah. J. Econ. Entomol. 82: 788-782.

Jones, V. P., S. L. Smith, and D. W. Davis. 1990. Comparing apple maggot adult phenology in eastern and western North America. IN: Dowell, R. V., L. T. Wilson, and V. P. Jones (eds), Apple maggot in the west, history, biology and control. University of California Division of Agriculture and Natural Resources. Publication #3341.