The effects of timing and rates of release of Phytoseiulus persimilis against two-spotted spider mite Tetranychus urticae on dwarf hops

Single inoculative releases of the phytoseiid mite Phytoseiulus persimilis were made against the two-spotted spider mite, Tetranychus urticae, on two varieties of dwarf hops in 1996 and 1997 at means of 20, 10, 5, 2.5 and nil per plant, and at up to three timings The numbers of spider mites recorded on leaves after the predators were released were related inversely to the rates of release. The earliest releases of the predator maintained spider mites at lower population densities than did those made later in the year. In all treatments the numbers of spider mites decreased when the prey;predator ratio reached approximately 10:1.