ABUNDANCE OF PHYTOSEIID MITES ON VITIS SPECIES - EFFECTS OF LEAF HAIRS, DOMATIA, PREY ABUNDANCE AND PLANT PHYLOGENY

We observed the number of predatory mites (phytoseiidae: Typhlodromus caudiglans) on the foliage of 20 North American species of grapes (Vitis spp) plus the domesticated European Vitis vinifera, all grown in a common garden. We found relatively few phytophagous mites. The numbers of phytophagous mites were not correlated with the plant characteristics that we measured. We found approximately five times as many predatory mites as phytophagous mites and the numbers of these phytoseiid predators were not affected by the availability of prey. Similarly, numbers of phytoseiids were unaffected by plant gender and, hence, the availability of pollen, another source of food. The numbers of phytoseiids were not clustered according to the taxonomic grouping of the tested plant species. Leaf surface characteristics explained over 25% of the variance in the numbers of phytoseiids. Numbers of phytoseiids were positively associated with the density of vein hairs, the density of bristles in leaf axils, and the presence of leaf domatia. These results suggest that sheltered habitats rather than food availability may limit the numbers of phytoseiid mites on grapevines.