Nonlinear responses of spider mites to drought-stressed host plants

Abstract. 1. This study examines the shape of the population response curve of the two-spotted spider mite, Tetranychus urticae Koch, feeding on bean plants, Phaseolus vulgaris L., which have been subjected to one of a range of drought stresses.
2. Abundance of spider mites declined at slight drought stress, increased at intermediate intensities of stress, and declined again at severe stress.
3. Fecundity showed the same pattern found for total abundance. Developmental rates of immatures, on the other hand, generally increased with stress intensity. Survivorship of immatures and adult females appeared unrelated to stress intensity.
4. These results indicate that responses of mites to drought-stressed beans are nonlinear. Such a pattern helps explain contradictory results obtained for spider mites and other arthropod herbivores.