Impact of Irrigation and Experimental Drought Stress on Leaf-Mining Insects of Emory Oak

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Abstract
The hypothesis that drought-stressed trees suffer higher levels of herbivory than unstressed trees was tested experimentally with two as yet undescribed species of Cameraria leaf miners. Densities and site selection of the species differ within a common host plant. Several roots of four trees in a wash were severed and four trees at a more xeric site were irrigated. Densities of leaf miners on the experimental trees and also on four control trees were monitored at each of the two sites. Both irrigation and root cutting affected foliar water content as expected. In apparent contrast to predictions of the "stress hypothesis," leaf miners occurred more frequently on irrigated trees than controls at the xeric site and were more abundant on control trees than those with cut roots at the wash. Survival of Cameraria at the wash did not differ between experimental and control trees. Stressed trees may have been severely, rather than moderately stressed and this may explain why miners preferred unstressed trees. Mortality due to parasitoids and predators appears much higher for miners at the drier site compared with those at the wash and may explain observed differences in densities of the leaf-mining insects.