Plants with spider-mite prey attract more predatory mites than clean plants under greenhouse conditions

Although many predators and parasitoids are known to respond to odours prod uced by plants infested with their prey under laboratory conditions, there are actually few studies that show that this response leads to higher numbe rs of predators or parasitoids on the plants under natural conditions. Here we study the response of predatory mites (Phytoseiulus persimilis Athias-H enriot, Acari, Phytoseiidae) to odours from cucumber plants infested with t wo-spotted spider mites (Tetranychus urticae Koch, Acari, Tetranychidae) in greenhouse release experiments, where predators were released in the centr e of a hexagon of cucumber plants. Forty to 57% of all predators released w ere recaptured on plants within 7 h. Of these, an average of 79.5% were fou nd on infested plants, indicating that these attract about 4 times as many predators as do clean plants. Hence, the blind predatory mites were guided to the plants with prey by herbivore-induced odours produced by the plant, as was indicated by olfactometer experiments, where it was found that P. pe rsimilis preferred odours from infested cucumber plants to odours from clea n cucumber plants. The long-range searching behaviour of P. persimilis is d iscussed.