CONSEQUENCES OF MITE FEEDING INJURY TO BEANS ON THE FECUNDITY AND SURVIVORSHIP OF THE 2-SPOTTED SPIDER-MITE (ACARI, TETRANYCHIDAE)

Fecundity and survival of the two-spotted spider mite, Tetranychus urticae Koch, were examined on bean (Phaseolus vulgaris L.) plants that had been subjected to mite feeding injury in the laboratory. Different numbers of T. urticae were restricted on the first two leaves of young bean plants, and spider-mite fecundity and survivorship was assayed on the third leaf. Each plant received four recently enclosed females, one female from each of four mite lineages. Using changes in the ratio of root mass to shoot mass of bean plants as a continuous measure of plant stress from spider-mite feeding, fecundity was positively related to stress for three out of four experiments. In two out of four experiments, survival of females was also positively related to stress, but reached an asymptote at slight or moderate stress levels. No evidence for induced resistance in beans was found. Mite lineage and the interaction between lineage and stress affected female survival but not fecundity. The implications of these results for understanding spider-mite outbreaks are discussed.