Flower nitrogen status and populations of Frankliniella occidentalis feeding on Lycopersicon esculentum

In a 2-year study, we manipulated flower chemistry of field grown Lycopersi con esculentum in North Florida and examined subsequent effects on populati ons of Frankliniella occidentalis. We examined variation in amino-acid prof iles and total nitrogen concentrations of flowers, flower number and plant size seasonally and in response to variable rates of nitrogen fertilization (202 kg ha(-)1 and 309 kg ha(-)1). Populations of F. occidentalis sampled every 6 to 10 days were then related to seasonal and treatment effects on p lant variables. For both years, F. occidentalis was abundant on L. esculent um tomatoes for only short intervals (2-3 weeks), and populations were sign ificantly higher on hosts receiving higher rates of nitrogen fertilization. Seasonal trends in F. occidentalis on L. esculentum were correlated to num ber of flowers per host plant, as well as concentrations of total nitrogen in flowers. Moreover, treatment (fertilization) effects were consistent wit h changes in the nitrogen status of flowers. Plants subjected to higher fer tilization rates produced flowers that had higher nitrogen content as well as variations in amino-acid profiles during the period of peak thrips popul ations. Abundance of F. occidentalis (particularly adult females) were most highly correlated to flower concentrations of phenylalanine during populat ion peaks. Our results are consistent with beneficial effects of high dieta ry nitrogen to thrips populations, and also support the hypothesis that aro matic amino acids (e.g., phenylalanine) play a central role in the nutritio nal ecology of F. occidentalis.