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

In a 2-year study, we manipulated flower chemistry of field grown Lycopersicon esculentum in North Florida and examined subsequent effects on populations of Frankliniella occidentalis. We examined variation in amino-acid profiles 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 plant variables. For both years, F. occidentalis was abundant on L. esculentum tomatoes for only short intervals (2-3 weeks), and populations were significantly higher on hosts receiving higher rates of nitrogen fertilization. Seasonal trends in F. occidentalis on L. esculentum were correlated to number of flowers per host plant, as well as concentrations of total nitrogen in flowers. Moreover, treatment (fertilization) effects were consistent with changes in the nitrogen status of flowers. Plants subjected to higher fertilization rates produced flowers that had higher nitrogen content as well as variations in amino-acid profiles during the period of peak thrips populations. Abundance of F. occidentalis (particularly adult females) were most highly correlated to flower concentrations of phenylalanine during population peaks. Our results are consistent with beneficial effects of high dietary nitrogen to thrips populations, and also support the hypothesis that aromatic amino acids (e.g., phenylalanine) play a central role in the nutritional ecology of F. occidentalis.