Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2012
Publication Date: 6/20/2012
Citation: Cha, D.H., Yee, W.L., Goughnour, R.B., Simm, S.B., Powell, T.H., Feder, J.L., Linn, Jr, C.E. 2012. Identification of host fruit volatiles from domestic apple (Malus domestica), native black hawthorn (Crataegus douglasii) and introduced ornamental hawthorn (C. monogyna) attractive to R. pomonella flies from the western U.S.. Journal of Chemical Ecology. 38:319-329. doi.10.1007/S10886-012-0087-9. Interpretive Summary: The apple maggot fly damages apple fruit and is a major quarantine concern for apple growers in the western U.S. Personnel at the USDA-ARS Yakima Agricultural Research Laboratory in Wapato, WA, University of Notre Dame, IN, and Cornell University, NY conducted tests to identify volatile blends from apple, black hawthorn, and ornamental hawthorn fruit that are attractive to apple maggot flies from Washington state. Flies that developed in apple, black hawthorn, and ornamental hawthorn responded highly to volatile blends isolated from their respective hosts. Results suggest that apple maggot flies in Washington may discriminate among fruit volatiles and that some fly populations there are not highly attracted to apples, lessening the threat of these flies to the apple industry.
Technical Abstract: The apple maggot fly, Rhagoletis pomonella, infests apple (Malus domestica) and hawthorn species (most notably the downy hawthorn, Crataegus mollis) in the eastern USA. Evidence suggests that the fly was introduced into the western USA sometime in the last 60 years. In addition to apple, R. pomonella also attacks two species of hawthorns in the western U.S. as major hosts: the native black hawthorn (C. douglasii) and the introduced ornamental English hawthorn, C. monogyna. Apple and downy hawthorn flies in the eastern USA use volatile blends emitted from the surface of their respective ripening fruit to find and discriminate among host trees. To test whether the same is true for western flies, we report using coupled gas chromatography and electroantennographic detection (GC-EAD) to develop a 7-component apple fruit blend for western apple-origin flies, an 8-component black hawthorn fruit blend for flies infesting C. douglasii, and a 9-component ornamental hawthorn blend for flies from C. monogyna. Crataegus douglasii and C. monogyna-origin flies showed similar levels of upwind directed flight to their respective natal synthetic fruit blends in flight tunnel assays compared to whole fruit adsorbent extracts, indicating that the blends contain all the behaviorally relevant fruit volatiles to induce maximal response levels. The black and ornamental hawthorn blends shared four compounds in common including 3-methylbutan-1-ol, which appears to be a key volatile for all R. pomonella populations showing a preference for hawthorn fruit. However, the blends also differed from one another and from domesticated apple in several respects that make it possible that western R. pomonella may behaviorally discriminate among fruit volatiles and form ecologically differentiated host races, as is the case for eastern apple and hawthorn flies.