Detection of an apple-infesting population of Rhagoletis pomonella (Walsh 1867) (Diptera: Tephritidae) in the state of Colorado, USA

The apple maggot fl y, Rhagoletis pomonella (Walsh 1867) (Diptera: Tephritidae), is an economically important pest of apples (Malus domesica Borkh.) (Rosaceae) throughout much of the United States. The fl y is endemic to the eastern U.S., where its primary host plants are several species of native hawthorns (Crataegus spp.) (Rosaceae). About 150 years ago the fl y shifted to apples in the Northeast. More recently, the fl y has been introduced to the western U.S. outside of its native range. In the state of Colorado, R. pomonella attacks the fruits of a number of different native and introduced hawthorn species, but is generally absent from apples. While orchards in apple growing regions are closely monitored, backyard and non-commercial apples often go largely unexamined. Here, we report results from a survey of non-commercial apples at 16 locations in eight counties across Colorado. We document the discovery of one R. pomonella infestation of apple at low density in Boulder, Colorado in close proximity to highly attacked, introduced downy hawthorn (C. mollis Scheele) in a residential neighborhood. Our fi nding represents the fi rst confi rmed infestation of apple in the state in 25 years. We discuss the implication of our fi ndings for apple maggot management.