Date of Award:

5-1-2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences: Biology

Committee Chair(s)

Diane G. Alston

Committee

Diane G. Alston

Committee

Edward W. Evans

Committee

Kelly L. Kopp

Abstract

In a series of field and laboratory experiments, I tested two entomopathogenic nematode species, two nematode concentrations, and three life stages of the economically damaging insect pest, Contrachelus nenuphar, to support the development of a biological control program for this pest in northern Utah. Two entomopathogenic nematodes, Heterorhabditis bacteriophora and Steinernema feltiae, were tested for their virulence. The population of H. bacteriophora tested was collected from soil infested with plum curculio in Brigham City, UT in 2002. The S. feltiae population was obtained from a commercial source. In temperature bioassays, the two nematodes species exhibited different thermal ranges. Both species performed best at 20 °C: insect mortality was fastest, nematode establishment was greatest, and nematode reproduction was highest; however, at 30 °C, H. bacteriophora outperformed S. feltiae and at 10 °C, S. feltiae was superior to H. bacteriophora in all of the factors. In insect life stage bioassays in the laboratory, H. bacteriophora was more virulent than S. feltiae for all plum curculio life stages. The adult and pupae were more susceptible than larvae based on maximum mortality; however, the time required to kill 50% of the population was faster for larvae. A higher concentration of 500 infective juveniles (IJs) per insect was more virulent than 100 IJs per insect for all life stages. In testing the field efficacy of the two species of entomopathogenic nematodes, nematodes were applied during June and July in 2005 and 2006 to plum curculio infested home yard fruit trees in Brigham City, northern Utah. The total concentration of nematodes applied was 437,000 to 1,640,166 infective juveniles per square meter in two years. After nematode applications, plum curculio adult densities were slightly reduced when compared to before spraying nematodes within the same year. However, adult plum curculio densities were significantly suppressed in sites where nematodes were applied for two and three years as compared to sites that received applications for just one year. Both species of nematodes successfully established in the soil of field sites after three to seven applications. My results suggest that two or more years of nematode applications targeting plum curculio pupae and adults in the soil with concentrations of 0.5 - 1.0 million IJs per m2 will significantly suppress plum curculio densities in fruit trees.

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