The abundance of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) was examined in north Florida from 2001 to 2003 on the following Vitis genotypes: V. rotundifolia Michx. (cultivars ‘Carlos’, ‘Early Fry’, ‘Regale’, and ‘Noble’), V. rupestris Scheele. (cultivars ‘St. George’ and ‘Constancia’), V. simpsoni Munson (cultivar ‘Pixiola’), V. champini Planch. (cultivars ‘Dogridge’ and ‘Ramsey’), and V. vinifera L. (cultivars ‘Chardonnay’, ‘Chenin blanc’, and ‘Exotic’). The mean number of adult H. coagulata was less than two per vine per day during 2001 and was lowest on V. rotundifolia cultivars. During June/July 2002, the number of leafhoppers varied between 2 per vine per day on V. rotundifolia cultivars and 10–20 per vine per day on the other Vitis genotypes. The distribution of H. coagulata was examined from June to September 2002 and during August 2003 in relation to the primary organic nutrients (19 amino acids, 7 organic acids, and 3 sugars) in xylem fluid. The concentrations of most amino acids varied with Vitis genotype. Glutamine represented between 58 and 89% of all amino acids. Leafhopper abundance was positively correlated with total amino acids and percentage glutamine and inversely correlated with many of the remaining amino acids. The percentage of proline in xylem fluid was the best inverse correlate to leafhopper abundance during 2002 and 2003. Consumption rates of H. coagulata were positively correlated to insect abundances. The adult to nymph ratio was over 10:1, and egg masses were only occasionally found on Vitis. These data suggest that adult H. coagulata used Vitis primarily as a feeding host. The ratio of glutamine to proline (GlnPro) was the most consistent chemical correlate to H. coagulata abundance and feeding. Glutamine and proline may play a behavioral role in determining H. coagulata host selection and consumption rates.
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