The leafmining fly Liriomyza sativae Blanchard is an important polyphagous pest of vegetables crops in the United States and around the world. Phylogeographic analysis of mitochondrial cytochrome oxidase I sequence variation indicates that L. sativae harbors distinct mitochondrial clades suggestive of the presence of cryptic species. Two of the major mitochondrial clades exhibited polyphagy, with members feeding on hosts in at least three plant families. Only one of the major clades was present in introduced populations, causing total mitochondrial variation exhibited by introduced populations to be considerably reduced compared with that observed within the native range.