Host-selection Behavior Differences between the Fruit Fly Sibling Species Rhagoletis pomonella and R. mendax (Diptera: Tephritidae)

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Abstract
Laboratory, field cage, and field experiments on natural populations revealed substantial differences in host-selection behavior exhibited by females of the sibling species Rhagoletis pomonella (Walsh) (which infests apple and hawthorn) and R. mendax Curran (which infests blueberry and huckleberry). In laboratory assays with a single fruit, R. pomonella attempted oviposition into apple and hawthorn more often than R. mendax, while R. mendax attempted oviposition more often than R. pomonella into highbush and lowbush blueberry and huckleberry. Oviposition responses similar to these were exhibited to the surface waxes of apple and blueberry transferred onto artificial fruit. In field-cage assays with a single potted apple tree, R. pomonella foraged longer in the tree and visited more leaves and fruit than R. mendax. In contrast, R. mendax spent more time and visited more leaves and fruit than R. pomonella when both species were tested on blueberry and huckleberry plants. Oviposition was exclusively limited to each species' natural hosts in the field-cage experiments. Studies of natural populations revealed that these species differed substantially in their alightment response to wooden fruit models of different size. Since R. pomonella and R. mendax appear to be interfertile in laboratory crosses, the behavioral differences documented here probably constitute one of the major barriers to their frequent interbreeding in nature.