The spatio-temporal dispersion patterns of adult leafhoppers (sampled with yellow sticky-boards)in deciduous orchards, apple,Malus silvestrisMiller, and nectarine,Persica vulgarisMiller, were studied using spatial autocorrelation statistics. Leafhoppers werc absent from the orchards before mid-May. Both,Asymetrasca decedens(Paoli) andEdwardsiana rosaeL., colonized the orchards followingthe blooming of trees. The 2 species were abundant in the apple orchard, producing 2 generations within the orchard.A. decedensdominated in the nectarine orchard, developing at least 1 generation within the orchard. Both species showed an aggregated spatial pattern at the edge of the orchards during the colonization wave. The spatial pattern ofA. decedensin both orchards changed from aggregated to random with each successive generation, and the population ofE. rosaemaintaincd aggregated pattems during the entire season. We suggest that the change in the aggregative pattern ofA. decedensresulted from the outward spread of the growing populations. Maintenance of the aggregative pattern byE. rosaewas probably related to both the outward spread of the population with each reproductive pulse and the successive colonization waves from the surrounding vegetation.