|POWELL, THOMAS - University Of Notre Dame|
|FEDER, JEFFREY - University Of Notre Dame|
|LINN, C - Cornell University - New York|
Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2018
Publication Date: 6/20/2018
Citation: Cha, D.H., Powell, T., Feder, J.L., Linn, C.E. 2018. Identification of a new blend of host fruit volatiles from red downy hawthorn, Crataegus mollis, attractive to Rhagoletis pomonella flies from the northeastern United States. Journal of Chemical Ecology. 44(7-8):671-680. https://doi.org/10.1007/s10886-018-0977-6.
Interpretive Summary: The Apple maggot fly is native to Eastern United States where its native host is Northern Red Hawthorn. However, in the mid 1800’s the fly shifted its native host to domestic apple and evolved new host fruit odor preferences and diapause traits, leading to the formation of a new host race on apple. The fly became a major pest on apples in the Eastern U.S. and is currently also a major quarantine concern for apple growers in the Western U.S., where it appeared in the 1970’s from shipments of apples from the Eastern U.S. Personnel at the USDA-ARS, U.S. Pacific Basin Agricultural Research Center in Hawaii, University of Notre Dame in Indiana, and Cornell University in New York have identified a new volatile blend from northern red hawthorn fruit that is as attractive to red hawthorn-origin flies as the previously identified blend. However, the new blend is more complex in the number of volatiles and provides evidence for volatiles from hawthorn fruit that are also found in the apple volatile blend, volatiles not identified in the earlier identification. This discovery helps explain the origin of the apple infesting host race by showing that hawthorn flies had the preexisting ability to detect the apple volatiles. Our results are important in that they suggest an odor-mediated mechanism for the shift of a native non-agricultural pest to become an agricultural pest.
Technical Abstract: A new blend of volatiles was identified for the fruit of Downy Red Hawthorn, Crataegus mollis, that is attractive to Rhagoletis pomonella flies infesting this host in the Northeastern U.S.A. The new blend was as attractive as the previously identified mixture but is more complex in the number of odorants (6 in the old versus 10 in the new) and differs significantly in the ratio of three volatiles (3-methylbutan-1-ol, butyl hexanoate, dihydro-ß-ionone) that are common to both blends and exerted agonist or antagonist effects on behavior in a flight tunnel assay. However, behavioral results with the old and new northern hawthorn blends, as well as modified blends with substituted ratios of 3-methylbutan-1-ol, butyl hexanoate, dihydro-ß-ionone, indicate that the ‘agonist’ or ‘antagonist’ effects of these volatiles depended on the ratio, or balance of compounds within the blend. In addition, the new blend contains a number of volatiles (esters) identified from the headspace of domesticated apple, Malus domestica, that are attractive to apple-origin R.pomonella, and present in the five other blends from southern hawthorns, including the southern C.mollis var. texana blend, but are not part of the previously identified blend from northern C.mollis fruit. This finding supports the hypothesis that in addition to providing specificity to the odor blends of the northern and southern hawthorn populations, the presence of the significant amounts of ester compounds in the new northern hawthorn blend might have provided a source of standing variation that could help explain the shift in host preference by C.mollis-infesting flies to introduced apple in the mid-1800’s.