I’m interested in the phylogeographic structure of the Colorado Potato Beetle (Leptinotarsa decemlineata). This beetle is a pest of potato and other related crops (Solanum spp.) in the United States, Europe, and Asia, but its diet was restricted to wild, weedy Solanum species and its range was limited to Mexico and the Central Plains prior to the mid-1800s (Hare 1991). The beetles in Mexico are not pests on potato (even though potato has been grown commercially in that country for most of the last century), and there is some evidence that there is genetically-based geographic variation in the propensity to feed and lay eggs on potato (Lu and Logan 1994, 1995). This information, in addition to the striking fixed color differences between southern Mexican and US populations, and significant Fst’s between Mexican and US populations (based on allozyme data; Hsiao and Jacobsen 1983) suggest that gene flow ceased some time ago. Using collections of beetles from several populations in Mexico and the United States, I want to test whether the divergence was ancient (yielding reciprocal monophyly in some gene trees) or more recent (paraphyly of Mexican populations with respect to the US populations). I plan to use sequence data from mitochondrial (COI and COII fragments) and nuclear loci to test this question. I will use the thermocyclers and the ABI sequencing machine to conduct this study.