EFFECT OF LEAF VARIEGATION IN EUONYMUS-JAPONICA ON TETRANYCHUS-URTICAE (ACARI, TETRANYCHIDAE)

When mated female T. urticae were allowed to feed freely on individual variegated leaves of Euonymus japonica, they preferred to forage on the green tissue. Green tissue of variegated leaves had 1.6% phenolics on a dry-weight basis, which represents 18.4% more than yellow tissue. Over the 9-d observation period, females on variegated leaves maintained the same fecundity as a cohort feeding on entirely green leaves with average phenolic content only 5.6% greater than that of variegated leaves. These results contrast with those where herbivores avoided green tissue of a variegated plant because of more substantial (140.6%) differences in the phenolic content of green and variegated tissue. We conclude that in the absence of a phenolic defense, the potential for pest injury is acute in variegated plants. On an undefended variegated plant, feeding is focused on the diminished green area that is critical for growth. The nature of phenolic production in plant tissue in relation to the resource-balance theory of plant defense, and its effectiveness in variegated plants is discussed.