Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2009
Publication Date: 11/5/2009
Citation: Yee, W.L., Chapman, P.S., Sheets, D., Unruh, T.R. 2009. Analysis of Body Measurements and Wing Shape to Discriminate Rhagoletis pomonella and Rhagoletis zephyria (Diptera: Tephritidae) in Washington state. Annals of the Entomological Society of America. 102(6):1013-1028.
Interpretive Summary: Apple maggot fly is an important quarantine pest of apples in the Pacific Northwest. Accurate identification of apple maggot fly is essential in protecting the apple industry because it is the basis for quarantine and control measures. However, the presence of the almost identical snowberry maggot fly, which does not attack apples, makes quarantine decisions and control efforts difficult. Personnel at the Yakima Agricultural Research Laboratory in Wapato, WA, are determining if wing shape can be used to improve discrimination of the two species of flies compared with the older method for discrimination, which uses body measurements. We found that wing shape discriminates the two species of flies with >98% accuracy. This result is important because it indicates that wing shape analysis can reduce errors in identifications that can lead to unnecessary control measures or that can lead to misplaced inaction, which can result in increased threats of flies invading apple orchards.
Technical Abstract: Apple maggot fly, Rhagoletis pomonella (Walsh), is a quarantine pest of apple in Washington state, and is morphologically almost indistinguishable from the snowberry maggot fly, R. zephyria Snow, which does not attack apples. Current methods used to distinguish R. pomonella from R. zephyria, such as use of ovipositor lengths and wing band ratios, are not completely reliable because of interspecies overlap in these measures. In this study, geometric morphometrics and canonical variates analysis (CVA) were used to determine if wing shape can be used to discriminate the two species in Washington state. Thin plate spline deformation grids and Bookstein shape coordinates indicated that the wing of R. pomonella has a more gradual curve near the tip than that of R. zephyria, giving it an overall more narrow appearance than the wing of R. zephyria, which is broader at the tip. Wing shape identified female R. pomonella with 98.5% accuracy and female R. zephyria with 99.0% accuracy. Wing shapes also varied among some populations of R. pomonella from different hosts and geographic localities. Wing shape analysis correctly identified 100% of flies whose identities were questionable based on ovipositor lengths. Wing shape in males also separated R. pomonella from R. zephyria. There were subtle differences between the wing shapes of female and male flies in both species. Results indicate that wing shape analysis using geometric morphometrics is effective at discriminating R. pomonella and R. zephyria in Washington state and appears to be an improvement over the use of current identification methods for problematic flies.