Abstract: Information on the physiological responses of plants to below-ground herbivory is sparse. Effects of root herbivory by Diabrotica virgifera Leconte and the interactions of herbivory and soil moisture on photosynthesis and water relations of maize (Zea mays) were examined in a greenhouse. Plants were infested with 0, 50 and 100 larvae of D. v. virgifera at the six-leaf stage of development and water stress induced to half of the plants in each treatment. The 100-larvae treatment removed 67% of the roots and the 50-larvae treatment removed 19.6% of the roots, as compared to uninfested controls. Fifty-five days after infestation, damaged plants had recovered as there were no significant differences in root volumes among the infestation levels. Measurements of photosynthesis, stomatal conductance and leaf relative water content were not significantly different among larval treatments at 7, 13, 24 and 30 days after infestation. When soil moisture was withheld, however, photosynthesis and stomatal conductance were significantly reduced. On day 24, water stressed plants infested with 100 larvae had a 23% decrease in photosynthesis as compared to well-watered plants that were uninfested. These results indicate the potential that maize plants have to tolerate root herbivory by D. v. virgifera and that the effects were greater when soil moisture was reduced.