Changes in potato leafhopper,Empoasca fabae(Harris), stage distribution on potato and snap bean were examined in 1984–1985 with the objective of determining whether invasions were of local or long-distance origin.E. fabaepopulations were routinely sampled in potato and snap bean fields emerging after firstE. fabaearrival in Rosemount, Minn. (4 June in 1984,9 May in 1985,0 cumulative degree days [CDD], base 8.4°C). Adults were first consistently collected on potato and snap bean 325–475 CDD in 1984, and several large influxes occurred 355–494 CDD in 1985. These invasions occurred when first-generationE. fabaewould have matured on undisturbed hosts, suggesting they were of local origin. With the first large increase inE. fabaenumbers, there was a shift in sex ratio (data available for 1985 only) from predominantly female to 50:50. There is some evidence for dispersal following harvesting or plowing of alfalfa, but invasion correlated best with heat unit accumulations sufficient for the development of F1progeny.