Rhagoletis pomonella

(Walsh, 1867)

Apple Maggot, Apple Maggot Fly, Railroad Worm

Rhagoletis pomonella is a tephritid fruit fly native to North America that has undergone a major shift from native hawthorn to cultivated apple within the last 150 years, making it a primary pest of apple production in the northeastern United States and southeastern Canada. The exhibits host race formation, with genetically distinct specializing on apple versus hawthorn that show differences in seasonal timing, neurochemistry, and patterns. It has been introduced to the western United States and is subject to intensive monitoring and efforts due to its economic impact on fruit exports.

Rhagoletis pomonella by Joseph Berger, Bugwood.org. Used under a CC BY 3.0 license.

Rhagoletis completa in walnut-02 by Walpole. Used under a CC BY-SA 3.0 license.

Rhagoletis completa in walnut-01 by Walpole. Used under a CC BY-SA 3.0 license.

Pronunciation

How to pronounce Rhagoletis pomonella: /ræɡoʊˈlɛtɪs pəˈmɒnɛlə/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

are small flies approximately 5 mm in length with a black body, white banding on the , and dark wings with a distinctive white spot and four oblique white bands. The wing pattern distinguishes it from most other Rhagoletis . Larvae are cream-colored maggots found tunneling through fruit flesh. are brown, barrel-shaped, and approximately 4-5 mm long. The species is most reliably distinguished from the closely related Rhagoletis zephyria by association and timing: R. pomonella shows more dispersed adult eclosure patterns with less pronounced peaks, and unchilled puparia have significantly higher eclosion rates (13.5-21.9%) compared to R. zephyria (1.2-1.9%).

Images

Habitat

Orchards and wild containing plants in the Rosaceae, particularly apple (Malus domestica) and hawthorn (Crataegus spp.). Found in temperate regions with sufficient chilling periods for pupal development.

Distribution

Native to eastern North America; now distributed across the United States including the Northeast, Midwest, and Pacific Northwest (Washington, Oregon, California), and throughout southeastern Canada. Present in Mexico. The western North American represent a known invasion from the native range, with recent spillover into British Columbia, Canada.

Seasonality

occurs in early summer following pupal , with timing varying by race and geographic location. Apple race typically emerge earlier than hawthorn race populations. In the Pacific Northwest, emergence has been modeled using heat accumulation thresholds for forecasting. Activity continues through summer and early fall, with late-season varieties particularly vulnerable to .

Diet

Larvae feed internally on the flesh of developing fruits. Primary are apple (Malus domestica) and hawthorn (Crataegus spp.); also recorded from plum, pear, cherry, and blueberry, though usually not a serious pest of these fruits. Crab apples are invariably infested.

Host Associations

Malus domestica - primary Cultivated apple; derived for the apple host race
Crataegus spp. - ancestral Native hawthorn; ancestral for the hawthorn host race
Prunus spp. - secondary Plums and cherries, usually minor
Pyrus spp. - secondary Pear, usually minor
Vaccinium spp. - secondary Blueberry and huckleberry, usually minor

Life Cycle

Complete with four stages: , larva, pupa, . Females lay eggs beneath the skin of fruits using a retractable ovipositor. Larvae develop within the fruit, feeding on the flesh for approximately 3-4 weeks before exiting to pupate in soil. Pupae enter and overwinter in soil, with adult the following spring or summer. Diapause timing differs between host races: apple race pupae exhibit adult brain three weeks faster after an identical simulated winter than hawthorn race pupae.

Behavior

Females show strong fidelity, preferring to oviposit in the host fruit in which they developed as larvae, contributing to reproductive isolation between host races. mate on host plants. Apple race flies exhibit more dispersed adult patterns with less pronounced peaks compared to hawthorn-origin .

Ecological Role

Herbivore and frugivore; larval feeding causes fruit damage and premature drop. Serves as for braconid Opius lectus and Biosteres melleus, though apple-infesting experience lower parasitoid attack rates (13%) compared to hawthorn-infesting populations (46%) due to fruit size providing physical protection, phenological asynchrony, and reduced heterospecific competition. The host race formation in R. pomonella is a classic example of ecological speciation in progress.

Human Relevance

Major economic pest of apple production, causing direct fruit damage and triggering restrictions that affect interstate and international trade. Subject to intensive survey and monitoring programs, such as the Washington State Department of Agriculture apple maggot survey program used to certify exports to China and Taiwan. Management includes trapping, applications, and attracticidal spheres. Environmental methods have been developed to detect the in green yard waste to prevent human-mediated spread. Climate-based forecasting models are used to optimize control timing.

Similar Taxa

Rhagoletis zephyria in western North America that attacks snowberry (Caprifoliaceae); distinguished by plant, more pronounced peaks, and lower unchilled pupal eclosion rates
Rhagoletis mendaxBlueberry maggot fly; attacks cultivated blueberries, historically the primary blueberry pest in New Jersey before displacement by spotted-wing drosophila
Drosophila suzukiiSpotted-wing drosophila, an vinegar fly that also attacks ripening fruit but belongs to a different (Drosophilidae) and has a serrated ovipositor for laying in intact fruit