Effects of Pacific Spider Mite on Physiological Processes of Almond Foliage1

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Abstract
Leaves of potted almond trees were exposed to varied population levels of Tetranychus pacificus McGregor. An inexpensive portable reflectance meter was used to nondestructively estimate chlorophyll concentrations of intact leaves. Chlorophyll content of the leaves was negatively correlated with the number of mite-days per leaf and positively correlated with the mean percent of unscarred surface area as determined visually. Gas exchange data were obtained under field conditions with a portable dual isotope (3H2O and 14CO2) porometer which allowed simultaneous estimation of photosynthesis and transpiration on the same intact leaves. The number of mite-days per leaf and visual estimates of damage were well correlated, negatively, with Ps and Ts rates. Photosynthetic rates were positively correlated with chlorophyll content of leaves. No gross physiological changes which could not be explained by mechanical damage were observed.