Trade-offs in performance on different plants may not restrict the host plant range of the phytophagous mite, Tetranychus urticae

We examined sib-mated lines of the phytophagous mite, Tetranychus urticae K och, for trade-offs in performance on different plants. We found no signifi cant trade-offs among 10 potential host plants examined. Trade-offs in perf ormance were not detected in most cases, even when the variations in genera l performance (mean performance on all potential host plants) among the sib -mated lines were statistically adjusted, denying the possibility that this may be due to the variations in general performance among the lines. No ev idence for trade-offs was obtained in an artificial selection experiment; o n all tested plants, a line adapted to one marginal host plant exhibited hi gher performance than the control line. However, the general performance se emed to be negatively correlated with other adaptive traits of the mite, su ch as competition ability of adult males for their mates and overcrowding r esponse of adult females. Such correlations may contribute to the maintenan ce of genetic variation in the general performance of T. urticae.