Documenting the Patterns and Ecological Impacts of a Densovirus on Melissa Blue Butterflies (Lycaeides melissa) and Beyond

Insects become infected with all major taxa of pathogens and represent convenient systems in which to study disease. Descriptions of the ecology and evolution of entomopathogens are essential for applications in biological pest control, assessing the consequences of disease in beneficial species, or expanding on general knowledge of disease dynamics. Insect-specific viruses from the family Baculoviridae are known for their host specificity and lethal effects, however, viruses (like their insect hosts) are enormously diverse and many avenues of their distribution and natural history remain unexplained. The focal pathogen of this dissertation is the Junonia coenia densovirus (JcDV), a single-stranded DNA virus that infects Lepidoptera and interrupts molting and respiration. The distribution and multi-scale effects of JcDV infection are still being described, as are important factors that influence the host-pathogen relationship across species of Lepidoptera. For my research, I combined field surveys with manipulative studies in the laboratory to characterize JcDV infection within and between host species. The Melissa blue butterfly ( Lycaeides melissa , Lepidoptera: Lycaenidae) was the focal host species for the first two chapters, which describe spatial and temporal patterns of JcDV infection at multiple levels. L. melissa is a multivoltine, non-migratory species that utilizes members of the Fabaceae plant family for oviposition and larval diet, with records of recent expansion to roadside alfalfa ( Medicago sativa ). Specifically, I investigated whether viral prevalence and load were influenced by factors such as host plant diet or adult collection time (Chapter One), then conducted a follow up experiment to study progression of infection and its diet-dependent effects on survival (Chapter Two). For these two studies, I utilized data collected from laboratory rearing and inoculation experiments, extensive field collections, and molecular-based approaches such as quantitative polymerase chain reactions (qPCR). Chapter One represents the first record of JcDV in wild-caught members of the Lycaenidae family (gossamer-winged butterflies). I found spatial variation of JcDV prevalence across sites of L. melissa , which suggests that viral exposure is different across populations and JcDV may be endemic in some. There was considerable variation in viral prevalence across and within seasons, such that certain years seemed to be "worse" for JcDV and prevalence was higher later in the season, which was composed of the third (or final) butterfly generation of the season. Since I did not detect virus in the community (other arthropods and plant surfaces) surrounding L. melissa , this result suggests that community transmission is less important in this system. These results highlight the importance of sampling multiple times over a season, especially in multivoltine species. For my second chapter, I conducted a rearing and inoculation experiment to understand the progression and outcome of infection in L. melissa as they relate to host plant quality, life stage, and condition. These data revealed a strong effect of host plant quality on determining whether individuals survived to adulthood in the challenge of JcDV infection. Mass (as a proxy of condition) and viral load were strongly influenced by diet quality, and different plant diets conferred different longevity in JcDV-infected adults. JcDV-infected individuals had faster development times and all individuals in the infected group had the virus upon death, regardless of life stage. Thus, host plant quality is important for determining the outcome of caterpillar-viral interactions. Additionally, this study reinforced prior data showing negative effects of alfalfa as an exotic host plant on L. melissa fitness. For the final chapter of my dissertation, I used qPCR to screen caterpillar waste (i.e., frass) samples collected from multiple potential host taxa and geographic regions, thereby expanding on our knowledge of the host and geographic range of JcDV. These results were the first record of JcDV in several lepidopteran families (with high viral frequency in Geometridae) and the Neotropics. The patterns of viral frequency depended on collection site and host plant diet. I performed nested PCR and Sanger sequencing on a capsid gene (VP) of JcDV to explore the possibility of host dependent genetic variation. Although ten haplotypes (i.e., variants) of the VP gene were identified, there was low genetic variation, leading us to conclude that JcDV is a well-conserved virus. The evidence of JcDV in frass also represents a nondestructive way to screen for viral infection, which is helpful in continuing to describe disease distribution and dynamics. Together, the findings of my dissertation demonstrate the variability in factors to be considered in multi-host, generalized pathogens, and broaden our understanding of JcDV as an emerging disease. Characterizing the distribution and host ranges of viruses in diverse host taxa is insightful for understanding general ecological and evolutionary processes of host-viral interactions.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctorate Degree

Grantor

University of Nevada, Reno

Year dc:date.issued

2024

Author dc:creator

• McKeegan, Kelli Joanne

Advisor dc:contributor.advisor

• Smilanich, Angela

Committee members dc:contributor.committeemember

• Forister, Matthew
• Teglas, Mike
• Voyles, Jamie
• Nuss, Andrew

• Densovirus
• Disease Ecology
• Lepidoptera
• Natural History
• Population Biology

Repository record dc:identifier.uri

https://scholarwolf.unr.edu/handle/11714/11002

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/11002