Reduction in Photosynthetic and Transpiration Rates of Alfalfa Caused by Potato Leafhopper (Homoptera: Cicadellidae) Infestations

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Abstract
Gas exchange rates of potted alfalfa, Medicago sativa L., grown under greenhouse conditions and infested with potato leafhoppers, Empoasca fabae (Harris), from an insectary culture were used to estimate reductions in photosynthesis and transpiration caused by infestations of 192, 120, 96, 72, 60, 36, 24, 12, and 0 leafhopper-hours, by caging 8, 5, 3, 1, or 0 insects on individual stems for 24 or 12 h. An exponential decay model fit the laboratory data, but halving exposure time doubled the decay coefficient, lambda. A cage effect was demonstrated by estimating increases in stomatal resistances that paralleled increases in the hours alfalfa was caged. Observed differences in lambda for the two exposures were attributed to this cage effect, but both measured values for lambda were different from zero. The nonzero slope of each line indicated that damage increased logarithmically with the density of leafhoppers. Quantified reduction in photosynthesis caused by these insects feeding under laboratory conditions will be useful in predicting yield loss in the field once the relationship between dry-matter production and photosynthesis is understood.

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