Variability in response specificity of apple, hawthorn, and flowering dogwood-infesting Rhagoletis flies to host fruit volatile blends: Implications for sympatric host shifts

Rhagoletis pomonella Walsh (Diptera: Tephritidae) originating from domesticated apple (Malus pumila), hawthorn (Crataegus mollis) (Rosaceae), and flowering dogwood (Cornus florida) (Cornaceae) were tested sequentially in flight-tunnel assays to volatile blends previously identified from the three fruit types. The majority of flies flew to odor sources containing their natal blend (68-83%). Some flies from each fruit type also flew to non-natal fruit blends (11-39%), but of these non-natal responders the vast majority were flies that responded to their natal blend as well. The results indicate that individual flies within R. pomonella populations infesting different host types have different degrees of specificity with respect to discriminating among fruit volatile blends, and that a moderate proportion of apple, hawthorn, and dogwood flies (10-30%) are broad responders, with the capacity to recognize and orient to more than one blend. The observed variability in response specificity could facilitate sympatric shifts to new host plants.