RESPONSE OF XYLEM-FEEDING LEAFHOPPER TO HOST-PLANT SPECIES AND PLANT-QUALITY

Carneocephala floridana, an oligophagous leafhopper that inhabits the salt marshes along the coasts of Florida, utilizes Borrichia frutescen s and Salicornia virginica (both herbs) as primary summer hosts, but u ses two grasses, Distichlis spicata and Spartina alterniflora, during the winter. We tested whether the seasonal patterns of abundance and a pparent host-switching by Carneocephala are related to plant quality. In laboratory experiments, nymphs of Carneocephala reared on nonfertil ized control plants of the two herbs produced adults that were similar in size to field-collected insects. Only Carneocephala raised at the lowest densities on Spartina and Distichlis from the highest fertilize r treatments produced adults similar in body mass to those reared on n onfertilized Borrichia and Salicornia. For Distichlis, superior qualit y (high foliar nitrogen) plants were able to mitigate the negative eff ect of nymphal crowding on adult body mass. However, laboratory fertil ization regimes produced an extremely high foliar nitrogen content in the two herbs and the organic acid concentration in the xylem fluid of Borrichia, the only host species suitable for xylem fluid extraction, increased 2.5- to 3-fold. Total amino acid concentration in the xylem fluid of fertilized Borrichia decreased compared to nonfertilized pla nts. Carneocephala demonstrated reduced feeding efficiencies on high n itrogen Borrichia. Our results suggest that Carneocephala prefers, and performs better on, plants with high nitrogen content up to a thresho ld, beyond which high nitrogen levels result in reduced leafhopper fee ding rates and assimilation efficiencies.