IPM of thrips in timothy and a density-independent effect on wing diphenism of grass thrips (Anaphothrips obscurus Muller).

摘要

Timothy (Phleum pratense L.) is an important cool season forage crop in Western states, primarily purchased on aesthetic appearance. Thrips (Anaphothrips obscurus Muller) have been implicated in quality reduction of this forage, but integrated pest management (IPM) is minimal. This dissertation addressed several IPM tenets: reliance on sampling, thresholds, alternative management tactics, and an ecological understanding of the system. Several sampling methods were compared for statistical consistency across time of day and season in Chapter 1. Rapping timothy tillers inside a plastic cup was the most consistent and fastest sampling method. Thrips densities were higher in the upper portion of the plant. Macropterous phenotypes were produced in late spring and throughout the summer; they dispersed as the summer progressed. In Chapter 2, differential thrips populations were created with disruptive insecticides. Thrips reduced hay quality and economic thresholds were established. Tetranychid mite populations were flared when cyfluthrin was used, but populations were not always present. Both thrips and mites affected yield, but quality degradation was a more consistent and common problem in these studies. Spring burning was investigated as an alternative physical management tactic in Chapter 3. Burning reduced populations in the short-term, although long-term management potential is questionable. In Chapter 4, the importance of density-independent effects on wing diphenism was tested by enclosing populations of thrips on timothy without and with nitrogen. Six weeks after fertilization, nitrogen had a direct effect on wing diphenism and a higher proportion of macropterous thrips were produced. This result was also obtained eight weeks after fertilization, but at this point in the study the differences in diphenism could have resulted from either a direct effect of nitrogen or an indirect effect of nitrogen, because there were more conspecifics in the nitrogen-treated timothy. Finally, the appendices detail a study on the precision of two sampling methods, a study on the effect of cyfluthrin calendar sprays on thrips, and several pilot growth chamber studies which investigated the effect of maternal wing diphenism, conspecific density, and nitrogen on offspring wing diphenism.