Mitochondrial DNA (mtDNA) was used to determine genetic diversity within and among prevalent Lygus species. Two pest species (L. lineolaris and L. borealis) are found in the Red River Valley of North Dakota and Minnesota. The emphasis has been on Lygus lineolaris because it is a widely dispersed pest in North America. Maternal lineages are being ascertained by using a DNA sequence of part of the mitochondrial cox1-cox2 region. Initially 1500 bp overlapping those two genes were sequenced in individuals originating from the Red River Valley, the Gulf Coast, New England, and its counterpart region of Canada. To sequence a larger number of samples with a single DNA sequencing pass we designed new primers that span about half the original longer sequence but contain a similar amount of variability. Preliminary data on L.lineolaris indicated local population diversity but little evidence for geographic genetic structure among widely dispersed North American populations. Insects from North Dakota, Mississippi, and Quebec have very similar mtDNA sequences, but a subset of insects collected in Connecticut appear to have distinctly divergent mtDNA. As an extension of this study, other prominent pest species (L. hesperus and L. elisus) are also being incorporated to provide a range of genetic diversity in this insect complex. To complement the mtDNA work we plan to examine microsatellite flanking sequences using loci and primers identified and provided by R. G. Foottit (Eastern Cereal and Oilseed Research Centre, Ottawa, Canada). These results could provide important information regarding the potential existence of host-specific or regional strains in the Lygus genus.