Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Larry P. Pedigo


The impact of potato leafhopper (PLH), Empoasca fabae (Harris), feeding on the yield and quality of alfalfa, Medicago sativa L., was investigated. Research was designed to characterize the physiological response of PLH-induced "hopperburn", with emphasis on individual plant components (i.e., stems and leaves). Field trials were conducted (one in 1984 and two in 1985) with field cages to establish known densities of PLH at two periods during second growth of 'Blazer' alfalfa. Plants were intensively sampled weekly to monitor stem and leaf development rates;Components comprising biomass yield were significantly altered as a result of PLH feeding. Although stem density was unchanged, the number of mainstem nodes and stem height were reduced. The effective leaf area index, which considers only non-chlorotic leaf tissue, was also significantly reduced for all infested plots. Growth rates for stem and leaf components indicate that initial delays in development from PLH stress are mostly compensated for later in the regrowth period;Measurements of forage quality, including digestibility, crude protein, and cell-wall concentration, were determined for all plots. Results demonstrate digestibility and cell-wall concentration are generally unaltered, but that leaf proteins are reduced. The relatively insignificant decline in quality is probably a result of the reduced stem component, offsetting the declines in leaf quality. Similar trends were noted for calculations of relative feed value, digestible dry matter intake, and digestible Oil, Gas, and Energy;The aggregate response in nutritional yield (biomass x quality) is significantly altered by PLH feeding. At harvest, the most significant correlation with PLH density was determined to be rate of phenological development. Economic-injury levels (EIL's) were calculated for alfalfa infested early and late based on days delay past first bloom. The calculations were made on a protein, digestible energy, and biomass equivalency for various control costs and market values;In order to evaluate the value of a PLH pest management system for specialized uses of alfalfa, damaged and undamaged characterizations were utilized in least-cost rationing models to refine the estimate of crop utility. The calculated values for crop utility enhance the use of economic decision indices for forage crops.



Digital Repository @ Iowa State University,

Copyright Owner

Scott Hasting Hutchins



Proquest ID


File Format


File Size

251 pages

Included in

Entomology Commons