The effect of non-glandular trichome patch size, trichome distribution, and interaction with pollen on predatory mite retention in grape

The abundance of the generalist phytoseiid mite Typhlodromus pyri Scheuten has been positively associated with non-glandular trichome density in grape plants. Experimental manipulation of trichomes was used to test a hypothesis that mite behavioral response to trichomes largely determines mite abundance. Cotton fiber trichome mimics on bean and grape leaves were used to investigate the effect of trichome patch size and distribution on predatory mite movement away from plants. In 72 h assays with bean seedlings, presence of cotton fibers more strongly influenced phytoseiid retention than fiber patch size or distribution on an individual bean plant. Three fiber patch sizes (6 cm², 3 cm², and two 3 cm²) all resulted in similarly greater retention than a no fiber control. Retention was also equivalent for a 6 cm² area of fibers placed as a whole over the leaf mid rib or divided into 10 randomly placed patches. The presence of pollen and fibers had an additive effect on T. pyri. In a longer 3 week population study with potted grape plants, adding fibers to the trichome-free grape cultivar Dechaunac increased both the number of adults and total motiles over the number found on plants with no added fiber patches. The number of adults recovered from Dechaunac plants with added fibers was equivalent to the number recovered from Baco, a cultivar with natural trichomes. The comparable response of T. pyri to artificial fibers on beans, a non-host, and on grapes indicates that trichome structures themselves and not host-specific volatiles contribute to observed retention patterns.