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Abstract

The effect of apple cultivar on the distribution of Amblyseius andersoni was studied in an experimental orchard where tetranychids were virtually absent and eriophyids reached low to moderate populations. Seven apple scab-resistant cultivars, showing some differences in their leaf morphology, were compared. Each cultivar was grafted onto three different rootstocks inducing increasing vigor. The intraplant distribution of A. andersoni was also studied by monitoring predator densities on basal and apical leaves. In the first year, the colonization of different cultivars by A. andersoni showed definite patterns, sometimes associated with the abundance of the eriophyid Aculus schlechtendali. In the second experimental season, eriophyids reached negligible levels and the effect of cultivar on A. andersoni abundance was less clear. Florina and N.Y. 18 491 cultivars were colonized in both years by relatively high phytoseiid numbers, while TSR 29T219 and Priscilla showed low populations in at least one season. The results observed on the remaining cultivars were intermediate or indefinite. The role of leaf pubescence on phytoseiid colonization is discussed.