CHARACTERIZATION OF THE NATURAL ENEMY COMMUNITY, WITH EMPHASIS ON ENTOMOPATHOGENS, FOR MANAGEMENT OF WESTERN CORN ROOTWORM (\u3ci\u3eDIABROTICA VIRGIFERA VIRGIFERA\u3c/i\u3e) IN WEST CENTRAL NEBRASKA

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae),the western corn rootworm (WCR), is a major pest of corn (Zea mays L.) in the United States and Europe. WCR management options comprise mainly transgenic hybrids, insecticide applications and crop rotation. WCR is highly adaptable to management practices and field-evolved resistance to transgenic corn, insecticides and crop rotation in the United States Corn Belt has been reported. Therefore, the motivation for this project was to look into alternative options for WCR management. The goal of this dissertation is to characterize the natural enemies from irrigated commercial cornfields in Nebraska and examine their potential as biological control agents of the WCR. We surveyed five cornfields to document populations of arthropod predators, entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Yellow sticky cards and dry pitfalls captured a diverse community of above-ground natural enemies but their impact on WCR population dynamics is unlikely. In the laboratory, we isolated EPF and EPN species from soil samples using a baiting technique with Galleria mellonella L. andTenebrio molitor L. Entomogenous fungi with a variety of ecological roles were detected in every cornfield. Entomopathogenic fungi made up the majority of isolates, primarily represented by Metarhizium, but other genera of known and potential EPF include Beauveria, Penicillium, Pseudogymnoascus, and Purpureocillium. In the laboratory, forty-eight strains were screenedagainst WCR larvae. Results showed thatMetarhizium anisopliae, M. robertsii, Pseudogymnoascussp. and BotaniGard (Beauveria bassiana) caused mortality higher than the control and should be explored further in field studies. Six strains that were tested against the WCR can also infect prepupae of western bean cutworm (Striacosta albicostaSmith), another damaging pest of corn in Nebraska. We also determined that EPN strains of Heterorhabditis bacteriophoraPoinar andSteinernema spp. are present in Western Nebraska cornfields. An inoculation project with commercial and New York strains of EPN did not cause significant mortality in WCR populations, potentially due to native Steinernemaspp. being present in the control plots. Describing the natural enemy community from WCR-infested fields is a necessary first step in the exploration of biological control as a management tool against this devastating pest. Advisors: Julie A. Peterson and Lance J. Meink

Integration of Plant Defense Traits with Biological Control of Arthropod Pests: Challenges and Opportunities

Crop plants exhibit a wide diversity of defensive traits and strategies to protect themselves from damage by herbivorous pests and disease. These defensive traits may be naturally occurring or artificially selected through crop breeding, including introduction via genetic engineering. While these traits can have obvious and direct impacts on herbivorous pests, many have profound effects on higher trophic levels, including the natural enemies of herbivores. Multi-trophic effects of host plant resistance have the potential to influence, both positively and negatively, biological control. Plant defense traits can influence both the numerical and functional responses of natural enemies; these interactions can be semiochemically, plant toxin-, plant nutrient-, and/or physically mediated. Case studies involving predators, parasitoids, and pathogens of crop pests will be presented and discussed. These diverse groups of natural enemies may respond differently to crop plant traits based on their own unique biology and the ecological niches they fill. Genetically modified crop plants that have been engineered to express transgenic products affecting herbivorous pests are an additional consideration. For the most part, transgenic plant incorporated protectant (PIP) traits are compatible with biological control due to their selective toxicity to targeted pests and relatively low non-target impacts, although transgenic crops may have indirect effects on higher trophic levels and arthropod communities mediated by lower host or prey number and/or quality. Host plant resistance and biological control are two of the key pillars of integrated pest management; their potential interactions, whether they are synergistic, complementary, or disruptive, are key in understanding and achieving sustainable and effective pest management

Characterization of the Natural Enemy Community, With Emphasis on Entomopathogens, for Management of Western Corn Rootworm (Diabrotica virgifera virgifera)

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the western corn rootworm (WCR), is a major pest of corn ( Zea mays L.) in the United States and Europe. WCR management options comprise mainly transgenic hybrids, insecticide applications and crop rotation. WCR is highly adaptable to management practices and field-evolved resistance to transgenic corn, insecticides and crop rotation in the United States Corn Belt has been reported. Therefore, the motivation for this project was to look into alternative options for WCR management. The goal of this dissertation is to characterize the natural enemies from irrigated commercial cornfields in Nebraska and examine their potential as biological control agents of the WCR. We surveyed five cornfields to document populations of arthropod predators, entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Yellow sticky cards and dry pitfalls captured a diverse community of above-ground natural enemies but their impact on WCR population dynamics is unlikely. In the laboratory, we isolated EPF and EPN species from soil samples using a baiting technique with Galleria mellonella L. and Tenebrio molitor L. Entomogenous fungi with a variety of ecological roles were detected in every cornfield. Entomopathogenic fungi made up the majority of isolates, primarily represented by Metarhizium, but other genera of known and potential EPF include Beauveria, Penicillium, Pseudogymnoascus, and Purpureocillium. In the laboratory, forty-eight strains were screened against WCR larvae. Results showed that Metarhizium anisopliae, M. robertsii, Pseudogymnoascus sp. and BotaniGard (Beauveria bassiana) caused mortality higher than the control and should be explored further in field studies. Six strains that were tested against the WCR can also infect prepupae of western bean cutworm ( Striacosta albicosta Smith), another damaging pest of corn in Nebraska. We also determined that EPN strains of Heterorhabditis bacteriophora Poinar and Steinernema spp. are present in Western Nebraska cornfields. An inoculation project with commercial and New York strains of EPN did not cause significant mortality in WCR populations, potentially due to native Steinernema spp. being present in the control plots. Describing the natural enemy community from WCR-infested fields is a necessary first step in the exploration of biological control as a management tool against this devastating pest

Characterization of the Natural Enemy Community, With Emphasis on Entomopathogens, for Management of Western Corn Rootworm (Diabrotica virgifera virgifera)

Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), the western corn rootworm (WCR), is a major pest of corn ( Zea mays L.) in the United States and Europe. WCR management options comprise mainly transgenic hybrids, insecticide applications and crop rotation. WCR is highly adaptable to management practices and field-evolved resistance to transgenic corn, insecticides and crop rotation in the United States Corn Belt has been reported. Therefore, the motivation for this project was to look into alternative options for WCR management. The goal of this dissertation is to characterize the natural enemies from irrigated commercial cornfields in Nebraska and examine their potential as biological control agents of the WCR. We surveyed five cornfields to document populations of arthropod predators, entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN). Yellow sticky cards and dry pitfalls captured a diverse community of above-ground natural enemies but their impact on WCR population dynamics is unlikely. In the laboratory, we isolated EPF and EPN species from soil samples using a baiting technique with Galleria mellonella L. and Tenebrio molitor L. Entomogenous fungi with a variety of ecological roles were detected in every cornfield. Entomopathogenic fungi made up the majority of isolates, primarily represented by Metarhizium, but other genera of known and potential EPF include Beauveria, Penicillium, Pseudogymnoascus, and Purpureocillium. In the laboratory, forty-eight strains were screened against WCR larvae. Results showed that Metarhizium anisopliae, M. robertsii, Pseudogymnoascus sp. and BotaniGard (Beauveria bassiana) caused mortality higher than the control and should be explored further in field studies. Six strains that were tested against the WCR can also infect prepupae of western bean cutworm ( Striacosta albicosta Smith), another damaging pest of corn in Nebraska. We also determined that EPN strains of Heterorhabditis bacteriophora Poinar and Steinernema spp. are present in Western Nebraska cornfields. An inoculation project with commercial and New York strains of EPN did not cause significant mortality in WCR populations, potentially due to native Steinernema spp. being present in the control plots. Describing the natural enemy community from WCR-infested fields is a necessary first step in the exploration of biological control as a management tool against this devastating pest

Environmental Tolerance of Entomopathogenic Fungi: A New Strain of Cordyceps javanica Isolated from a Whitefly Epizootic Versus Commercial Fungal Strains

A new strain of Cordyceps javanica (wf GA17) was observed causing widespread epizootics among whiteflies in Southern Georgia in 2017. The tolerance of conidia to environmental factors including variable temperature and ultraviolet (UV) light was compared between this strain and three commercial strains of entomopathogenic fungi (Metarhizium brunneum F52, Cordyceps fumosorosea Apopka97, and Beauveria bassiana GHA). Under 10–30 °C, C. javanica wf GA17 responded similarly to other fungi, with the highest virulence against Galleria mellonella at 25 °C, followed by 20, 30, and 15 °C; lowest virulence was observed at 10 °C. At 35 °C and 40 °C, C. javanica wf GA17 had lower tolerance than M. brunneum F52 and B. bassiana GHA, but was superior to C. fumosorosea Apopka97 in conidia viability and post-treatment virulence. After exposure to −20 °C for 56 d, C. javanica wf GA17 exhibited lower germination than M. brunneum F52 and lower virulence than M. brunneum F52 and B. bassiana GHA, but higher germination and virulence than C. fumosorosea Apopka97. Following exposure to strong UV light, viability and virulence of all fungi were reduced with increasing exposure periods. Increased environmental tolerance of C. javanica wf GA17 over C. fumosorosea Apopka97 suggests that the new strain could have applicability for commercial pest management