Potato leafhopper (Homoptera: Cicadellidae) feeding disruption of phloem translocation in alfalfa

Histological and artificial injury (leafhopper injury simulation) studies of potato leafhopper. Empoasca fabae (Harris), injury to alfalfa, Medicago sativa L., have suggested that leafhopper feeding disrupts photosynthate translocation. To test directly for this disruption, we compared the distribution of radioactive, CO2-derived photosynthate in leafhopper-injured and healthy (uninjured) alfalfa stems. Exposure to two adult potato leafhoppers, confined for 3 d on the top 10 cm of alfalfa stems, reduced the upward flow of labeled translocate to the stem tips 300-fold and produced an accumulation of assimilates in the lower stem 2.4 times that of uninjured stems. Similar disruptions of translocation were achieved by caging two leafhopper adults for 6 h to the fourth internodes of stems. Stem exposure for these shorter durations resulted in a 3.7-fold decrease in tagged photosynthate at the tips of injured stems. Also, twice as much tagged translocate was found at the leafhopper-exposed site compared with the same internode of uninjured stems. No evidence of recovery by alfalfa from such phloem disruption, resulting from a 6 or 12 h exposure to two adult leafhoppers, was found 4 d after leafhopper removal