The goal of this research project is to understand how the apple maggot fly, Rhagoletis pomonella, a major pest of apples, can form populations that specialize on different species of its native hawthorn food plants in the southern United States. Unlike insects such as grasshoppers, where all individuals of a given species can and do eat a wide range of food plants, the apple maggot and similar insects form local populations (termed "host races") that feed within the fruits of only one or a few plant species. To understand how they do this, fly populations attacking different species of hawthorns in the southern United States will be tested to determine: 1) if they preferentially orient toward the chemical odor of the fruit of the hawthorn species they infest--this is how the flies find their host plants in nature to mate on and lay eggs into fruit, 2) if the timing of the life cycle of the flies is adapted to differences in when the various hawthorn trees fruit--some southern hawthorns fruit very early in the season (May) and some late (October-November), and 3) the degree to which any observed differences in odor response and life cycle are genetically based.
The broader impacts of the research are multi-faceted, having both important applied and basic benefits. Insects frequently shift their feeding to new crops. The apple maggot fly is a classic example, having shifted in the last 100 years from native hawthorns of little commercial interest to introduced apples of great economic value. Information about how this process occurs, which will be provided by research on southern hawthorn flies, is needed for better management of pests. For example, Rhagoletis pomonella flies from apple are repelled by the odor of red hawthorn, and vice versa, leading to the possibility that even better natural repellent odors might be found among the various southern hawthorn species. The project is also of basic scientific interest because shifts onto novel plants may serve as a trigger for speciation for many host specific insects. Finally, the project will provide important additional societal benefits by helping integrate science training and education across the local, community, and university levels
