COS 309-3 - Taking natural surveys to the lab: Describing infection patterns of a recently-discovered insect densovirus in a western North American Lycaenid

Abstract: Understanding host-pathogen relationships in natural systems requires knowledge of the patterns of infection at the individual level. Studying the effects of life stage, host diet, and maternal infection status on disease progression helps inform us of pathogen transmission strategies along with the ability of the host to eliminate or tolerate infection. The Junonia coenia densovirus (JcDV) was first discovered in the buckeye (Junonia coenia) but has since been discovered to infect multiple species of Lepidoptera. JcDV is contracted orally by larvae and causes hypoxia and interruption of molting, often leading to death before adult emergence. The Melissa blue (Lycaeides melissa) is a multivoltine, sexually dimorphic butterfly that exists in genetically isolated populations across western North America. It specializes on native species of legumes, but has recently been found to incorporate non-native alfalfa (Medicago sativa) as an exotic host. In our preliminary indication that JcDV infects wild Lycaenids, we found compelling variation of viral frequency and load across populations of L. melissa adults. In this study, we reared larvae from wild-caught L. melissa females from a subset of populations, on different host plants. Larvae were infected with JcDV at the third instar and monitored for condition (i.e. mass) and survival. Additionally, frass was collected for a measure of virus eliminated into the environment, and a subset of larvae were sacrificed at 2-day increments post-inoculation to be screened for viral load. Larvae sacrificed four days after inoculation had the highest viral burden, with average load decreasing afterwards, and individuals reared on M. sativa had the highest viral load. JcDV-infected individuals developed faster and had lower final mass than controls (regardless of host plant), but there were host plant effects on survival to adulthood. The results of this study help us describe the course of infection in this particular host-pathogen system, and uncover possible transmission strategies of the virus and disease resistance abilities of the host. By investigating the patterns of infection through manipulation in individuals, we can begin to understand the disease dynamics and ecological interactions of entomopathogens in the wild.