Leaf hairs influence searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis (Acari : Phytoseiidae)

The effect of leaf hairs on searching efficiency of adult female Phytoseiul us persimilis was investigated. For this purpose we used the ornamental cro p Gerbera jamesonii and determined the predator's searching efficiency on t hree cultivars that differ largely in the density of leaf hairs on the unde rsurface of the leaves. Walking speed of the mites was highest on the culti var with the lowest leaf hair density. Walking activity, defined as the per centage of time spent walking, was not dependent on leaf hair density of th e cultivars. At both prey densities tested, time until first predation incr eased with leaf hair density. The predation rate of adult female P. persimi lis is affected by trichome density, particularly when prey density is low. At prey densities of 1.3 and 2.5 Tetranychus urticae eggs cm(-2), predatio n rate was inversely related to leaf hair density. At a prey density of 8.0 eggs cm(-2) no significant effect of leaf hair density on predation rate w as found. These negative effects on searching efficiency and predation succ ess at low prey density of P. persimilis suggest that biological control of T. urticae on gerbera may be hampered by leaf hairs. Exp Appl Acarol 23: 1 19-131 (C) 1999 Kluwer Academic Publishers.