9508559 FEDER The Tephritid fly Rhagoletis pomonella is of interest to both farmers and population biologists alike. Not only are these flies major economic pests of apples, but they may also be in the process of speciating. Although R. pomonella is commonly referred to as the "Apple Maggot", apples are not the native host plant of these flies. That distinction belongs to hawthorns (thornapples). In the mid-1800's a portion of the R. pomonella populations in the Hudson Valley region of New York shifted from hawthorns and started attacking apples as a new host plant. Since then, apple-infesting populations of R. pomonella have spread across the eastern United States and have recently been introduced into California, Oregon and Washington. Genetic studies indicate that apple and hawthorn populations of R. pomonella are partially isolated entities. Six genes consistently display frequency differences between the apple and hawthorn fly races. These studies suggest that Rhagoletis flies may speciate sympatrically (i.e. without geographic isolation) in the process of specializing on new host plants. The goals of the proposed research are two-fold:1.) To ascertain how R. pomonella has adapted its life history to allow it to successfully attack apples as a new host plant. 2.) To determine the role that such changes in life history play in isolating apples from hawthorn races of the fly. Because R. pomonella flies have only one generation per year and adults live for only about a month, there is strong selection pressure on apple and hawthorn flies to match their development to that of their respective host plants. To test this hypothesis, Dr. Feder will manipulate rearing conditions for flies in the laboratory to induce environment dependent changes at the six genetic markers differing between the host races. In effect, he will be attempting to genetically transform the hawthorn host race into the apple race (and vice-versa) by selecting on hawthorn flies as if they were infesting f ruits with the earlier phenology of apples. What will we learn from the proposed research? First, the experiments will elucidate whether and how R. pomonella has altered its life history so that it can attack apples. Second, the results will pinpoint which environmental factors are most important for R. pomonella to overcome in a successful host shift. By subsequently measuring the intensity with which these factors act in the field, it will be possible to gauge how effective host-associated selection is at reproductively isolating apple and of the development traits adapting R. pomonella to apples. Such information will aid us in devising new measures to control the Apple Maggot and other fruit fly pests. The results will also help us predict what crops are potentially vulnerable to attack by Rhagoletis, as this pest spreads into new, fruit growing regions of the United States. Dr. Feder also has a strong commitment to transfer knowledge of population biology to others. This CAREER grant will also allow him to continue to pursue his teaching interest. He will teach a series of three classes at the undergraduate and graduate levels, exposing students to the general principles and concepts that form the basis for this and other research in population biology & systematics.
