SPATIAL SCALE OF AGGREGATION IN 3 ACARINE PREDATOR SPECIES WITH DIFFERENT DEGREES OF POLYPHAGY

Aggregative responses by the predatory mites, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseii dae), to spatial variation in the density of mobile stages of Tetranyc hus urticae (Acari: Tetranychidae) were studied over different spatial scales on greenhouse roses. Significant spatial variations in prey nu mbers per leaflet, per leaf, per branch or per plant were present in a ll experimental plots. None of the predator species responded to prey numbers per plant, and all searched randomly among plants. Within a pl ant, the oligophagous P. persimilis searched randomly among branches, but aggregated strongly among leaves within a branch and among leaflet s within a leaf. The narrowly polyphagous T. occidentalis searched ran domly among leaflets within a leaf and among leaves within a branch, b ut aggregated strongly among leaflets or leaves within a plant. The bo radly polyphagous A. andersoni searched randomly among leaflets within a leaf, a branch or a plant, and among leaves within a branch or a pl ant, but distributed themselves more often on branches with lower prey densities. Thus, specialist predators aggregate strongly at lower spa tial levels but show random search at higher spatial levels, whereas g eneralist predators show random search at lower spatial levels but agg regate at higher spatial levels. This is the first empirical evidence demonstrating the relation between the degree of polyphagy and the spa tial scale of aggregation. It is also concluded that both the prey pat ch size (i.e. grain) and predator foraging range (i.e. extent) are imp ortant for analyzing spatial scales of predator aggregation. The impor tance of studying spatial scale of aggregation is also discussed in re lation to predator-prey metapopulation dynamics.