Identification of host fruit volatiles from snowberry (Symphoricarpos albus), attractive to Rhagoletis zephyria flies from Western United States

Authors: CHA, DONG - CORNELL UNIVERSITY; OLSSON, SHANNON - CORNELL UNIVERSITY; Yee, Wee; GOUGHNOUR, ROBERT - WASHINGTON STATE UNIVERSITY; HOOD, GLEN - UNIVERSITY OF NOTRE DAME; MATTSSON, MONTE - PORTLAND STATE UNIVERSITY; SCHWARZ, DIETMAR - WESTERN WASHINGTON UNIVERSITY; FEDER, JEFF - UNIVERSITY OF NOTRE DAME; LINN, CHARLIE - CORNELL UNIVERSITY

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2017
Publication Date: 2/1/2017
Citation: Cha, D., Olsson, S., Yee, W.L., Goughnour, R., Hood, G., Mattsson, M., Schwarz, D., Feder, J., Linn, C. 2017. Identification of host fruit volatiles from snowberry (Symphoricarpos albus), attractive to Rhagoletis zephyria flies from Western United States. Journal of Chemical Ecology. 43(2):188-197.

Interpretive Summary: Apple maggot fly is a pest of apples whose responses to fruit volatiles have been well studied, helping us understand the process of speciation in insects that attack plants. However, responses by a similar fly, Rhagoletis zephyria, to chemicals from host fruit have never been studied. Personnel at the USDA-ARS Yakima Agricultural Research Laboratory in Wapato, WA, Cornell University in NY, University of Notre Dame in IN, Portland State University in OR, and Western Washington University in WA used gas chromatography and electroantennogram detection (EAD) to identify volatiles from the fruit of snowberry as key attractants for R. zephyria flies reared from snowberry fruit. A nine-component blend was identified that gave consistent EAD activity, and in a flight tunnel, snowberry flies displayed greater levels of upwind oriented flight to sources with snowberry than apple and hawthorn fruit volatiles. Findings suggest differences among flies in their behavioral responses to host fruit odors represent key adaptations involved in host plant shifts.

Technical Abstract: Gas chromatography coupled with electroantennogram detection (GC-EAD) was used to identify volatiles from the fruit of Snowberry, Symphoricarpos albus laevigatus, as key attractants for Rhagoletis zephyria flies reared from snowberry fruit. A nine-component blend containing 3-methylbutan-1-ol (3%), dimethyl trisulfide (1%), 1-octen-3-ol (40%), ß-myrcene (8%), nonanal (9%), linalool (13%), (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT, 6%), decanal (15%), and ß-caryophyllene (5%) was identified that gave consistent EAD activity. In flight tunnel assays, snowberry flies from two sites in Washington state, USA, displayed significantly greater levels of upwind oriented flight to sources with the snowberry volatile blend compared with previously identified volatile blends from domestic apple (Malus domestica) and downy hawthorn (Crataegus mollis) fruit from the eastern USA, and domestic apple, black hawthorn (C. douglasii) and ornamental hawthorn (C. monogyna) from Washington state. Selected subtraction assays showed that whereas removal of DMNT or 1-octen-3-ol significantly reduced the level of upwind flight, removal of ß-myrcene and ß-caryophyllene, or dimethyl trisulfide alone did not significantly affect the proportion of upwind flights. Our findings add to previous studies showing that populations of Rhagoletis flies infesting different host fruit are attracted to unique mixtures of volatile compounds specific to their respective host plants. Taken together, the results support the hypothesis that differences among flies in their behavioral responses to host fruit odors represent key adaptations involved in sympatric host plant shifts, contributing to host specific mating and generating prezygotic reproductive isolation among members of the R. pomonella sibling species complex.