Spatiotemporal within-plant distribution of the spider mite Tetranychus urticae and associated specialist and generalist predators A. Walzer 1 * , K. Moder 2 and P. Schausberger 1 1 Institute of Plant Protection, Department of Applied Plant Sciences and Plant Biotechnology, University of Natural Resources and Applied Life Sciences, Vienna, Austria: 2 Institute of Applied Statistics and Computing, Department of Landscape, Spatial and Infrastructure Sciences, University of Natural Resources and Applied Life Sciences, Vienna, Austria Abstract Predators are important determinants of the spatiotemporal distribution of prey within a given habitat. The predator effects may vary with diet specialisation, the associated risk posed to prey and, if multiple predators are present, the predator- predator interactions. We examined the spatiotemporal distribution of the her- bivorous spider mite Tetranychus urticae and the associated specialist and generalist predators Phytoseiulus persimilis and Neoseiulus californicus on bean plants. Tetranychus urticae is a key pest on numerous agricultural crops. Both predators are used singly and in combination for biological control of spider mites. Population development and within-plant distribution of the spider mites and the predators were compared among five treatments: T. urticae without predators, with either predator alone and with both predators in combination at full and half densities. The spider mites were suppressed to zero density in both predator combination treatments but not in the single predator treatments. The predators determined the spatiotemporal distribution of the spider mites through density- and behaviour-mediated effects, and these effects were linked to diet specialisa- tion. The specialist P. persimilis exerted stronger density-mediated effects on the spider mite distribution than did the generalist N. californicus. Either predator induced in the spider mites early upward migration on plants. The predators also affected each other’s distribution. The aggregation level of N. californicus was lowered by P. persimilis but not vice versa. In combination, the predators were more dispersed than when alone, reducing the predator-free space and leading to the local extinction of T. urticae. Keywords: Tetranychidae, Phytoseiulus persimilis, Neoseiulus californicus, disper- sion, aggregation, anti-predation behaviour, density-mediated effects, behaviour- mediated effects (Accepted 22 August 2008) * Author for correspondence Fax: +43 1 47654 3359 E-mail: andreas.walzer@boku.ac.at Bulletin of Entomological Research (2009) 99, 457–466 doi:10.1017/S0007485308006494 Ó 2009 Cambridge University Press Printed in the United Kingdom First published online 21 January 2009