The biology of Hyaliodes vitripennis Say (Heteroptera: Miridae) and its potential for biological control of mites and aphids were studied for 3yr in apple orchard settings. Results showed a significant repressive effect of H. vitripennis on the European red mite, Panonychus ulmi Koch, the two-spotted spider mite, Tetranychus urticae Koch and a significant augmentative effect on the green aphids (Aphis pomi DeGeer and Aphis spiraecola Pagenstecher). The predator also precluded the action of naturally occurring predatory mites, either by resource competition or by direct predation, but the resultant effect was always detrimental to P. ulmi.