Beet leafhoppers, Circulifer tenellus, collected from New Mexico were compared to a population obtained from California to determine if they were the same biotype. The insects were compared using PCR, morphology, distribution, physiology, life history, behavior and reproductive capabilities. Host preference has greatly impacted these aspects primarily, due to the lack of preference for the New Mexico leafhopper for sugar beets, which is a preferred host for California populations. Our results suggest that those leafhoppers constitute distinct biotypes.