Author ORCID Identifier

https://orcid.org/0000-0001-8278-8767

Year of Publication

2021

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department/School/Program

Entomology

First Advisor

Dr. Bruce Webb

Abstract

Helicoverpa zea nudivirus 2 (HzNV-2) is the only known sterilizing and sexually-transmitted insect virus and causes pathological symptoms in H. zea reproductive tissues. HzNV-2 has features that make it a candidate as a H. zea (corn earworm) control agent, such as the ability to cause asymptomatic (latent) and symptomatic (lytic) infections and the ability to influence mating behavior of its host to favor virus spread. HzNV pathology has been studied and its genome sequenced, however, its prevalence in natural populations is largely unknown. In this study, we developed and used a low-cost PCR-based molecular survey to investigate HzNV-2 prevalence and found that the virus is circulating in the southeastern United States and reaches up to 40% incidence in some areas. We also discovered a novel nudivirus infecting Heliothis virescens populations in some areas of Louisiana and Mississippi. This is the first multi-year study that uses molecular methods and sampling techniques to understand HzNV prevalence in feral Heliothine populations. To further investigate the prevalence of nudiviruses in Lepidoptera, data mining and bioinformatic tools were used to investigate the presence of nudiviruses in NCBI's publicly available sequence databases. This digital survey revealed significant nudivirus prevalence in both Helicoverpa armigera and Helicoverpa zea populations in Brazil, China, Greece, and Australia. Because the greater genetic complexity of H. armigera nudivirus than HzNV-2, we propose that HzNV-2 originally evolved with H. armigera as a host and spread to the Americas as a result of migration and speciation processes that occurred approximately 1.5 Mya. This idea is supported by additional nudivirus detections in a H. armigera population and in some Bombyx mori cell lines in the old world. Lastly, we sequenced a novel nudivirus that infects Heliothis virescens populations and analysis of this sequence revealed a 93.52% similarity to HzNV-2 the genome as well as an incomplete variant derived from the original virus. This in silico finding suggests the presence of a defective interfering particle that replicates and possibly competes with the original Heliothis virescens nudivirus (HvNV). In summary, this work establishes that nudiviruses are present in multiple Heliothine and other lepidopteran species and can be common enough to act as a natural agent controlling these populations. These findings support development of sterilizing nudiviruses as potential agents for novel strategies to control important lepidopteran pests.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2021.449

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