GEOSTATISTICAL ANALYSIS OF LEAFHOPPER (HOMOPTERA, CICADELLIDAE) COLONIZATION AND SPREAD IN DECIDUOUS ORCHARDS

The spatio-temporal dispersion patterns of adult leafhoppers (sampled with yellow sticky-boards) in deciduous orchards, apple, Malus silvest ris Miller, and nectarine, Persica vulgaris Miller, were studied using spatial autocorrelation statistics. Leafhoppers were absent from the orchards before mid-May. Both, Asymetrasca decedens (Paoli) and Edward siana rosae L., colonized the orchards following the blooming of trees . The 2 species were abundant in the apple orchard, producing 2 genera tions within the orchard. A, decedens dominated in the nectarine orcha rd, developing at least 1 generation within the orchard. Both species showed an aggregated spatial pattern at the edge of tile orchards duri ng the colonization wave. The spatial pattern of A. decedens in both o rchards changed from aggregated to random with each successive generat ion, and the population off. rosae maintained aggregated patterns duri ng the entire season. We suggest that the change in the aggregative pa ttern of A. decedens resulted from the outward spread of the growing p opulations. Maintenance of the aggregative pattern by E. rosae was pro bably related to both the outward spread of the population with each r eproductive pulse and the successive colonization waves from the surro unding vegetation.