The majority of life history traits of the egg, nymph, and adult stages of the potato leafhopper,Empoasca fabae(Harris), are adversely affected when they use water-stressed alfalfa (Medicago sativaL.). The consequences of these changes at the population level were examined by constructing life history statistics for cohorts on well-watered, moderately, and severely stressed alfalfa at the early regrowth and bud stage. The net reproductive rate declined with the increase in plant water stress for cohorts on both plant growth stages. The intrinsic rate of increase (rm) decreased when expressed on both a day and a degree-day basis. On early regrowth alfalfa,rmvalues on a centigrade degree-day basis were 0.0064, 0.0049, and 0.0039 for the control, moderate, and severe treatments, respectively. On bud stage alfalfa,rmvalues were 0.0049, 0.0041, and 0.0031 for the same treatments. The higher temperatures found in water-stressed fields were insufficient to compensate for the lowerrmof populations in these treatments. Coupled Leslie matrices were used to model the growth of leafhopper populations during one alfalfa growth cycle. These simulations show a 41 and 54% decline in total population size at harvest for the moderate and severe treatments, respectively. Data from water-stressed field plots were used to validate results from the controlled environment studies. Similar responses were found for immature developmental period, adult fecundity, and nymph population size. These results indicate that data obtained at a relatively constant water potential in a controlled environment can be used to approximate those values under the more variable conditions found in the field.