Physiological Response of Alfalfa to Injury by Empoasca fabae (Homoptera: Cicadellidae)

Under field conditions, densities of 0, 4, or 8 adult female potato leafhoppers, Empoasca fabae (Harris), were caged on individual alfalfa plants during the second and second-third crop growth cycles. Plants were destructively sampled three times in each crop growth cycle. Injury by E. fabae caused the percentage of total nonstructural carbohydrates to be much higher in leaves of infested plants. Leaf photosynthesis of plants caged with 4 or 8 E. fabae was reduced by 60 and 80%, respectively. The effects of feeding by E. fabae on leaf transpiration were very similar to that shown for photosynthesis. Stomatal resistance increased from <1 s cm−l on uninfested plants to >11 s cm−1 on infested plants. Leaf crude protein of plants infested with either 4 or 8 E. fabae was reduced by 22–35% after only 1 wk of leafhopper feeding.