Host Plant Chemistry and Infection Status Alters the Immune Response and Development Time in Vanessa cardui

Abstract

Studies investigating the interplay between the animal immune response and life history traits fall under the umbrella of ecoimmunology. An important goal of ecoimmunology is to understand the tritrophic interactions influencing insect immunity and survival. This study focuses on the effects of diet and pathogen infection on the immune response of the polyphagous butterfly, Vanessa cardui (Nymphalidae). Specifically, this study aims to understand the life history tradeoffs V. cardui experiences when fighting pathogens and whether these tradeoffs are diet dependent. I hypothesized that V. cardui larvae infected with the entomopathic virus, Junonia coenia densovirus (JcDNV), would have two avenues for surviving the virus: invest in development or mount an immune response. I demonstrate that the ability to invest in one or the other is dependent on diet and infection status. I found that V. cardui reared on plant diets responded to the JcDNV infection by developing quicker than uninfected individuals. Infected individuals also had a lower immune response compared to the uninfected group. However, when larvae were reared on a more nutrient rich diet (artificial diets) there was no effect of virus infection on development time, suggesting that the impact of the virus on development time is nutrient related. I also found that other dietary factors (iridoid glycosides found in the novel host plant Plantago lanceolata) can provide additional protections (faster development and higher immunocompetence) compared to the native host plants Lupinus argenteus and Lupinus albifrons. Therefore, I suggest that diet impacts the effects of JcDNV and influences the course of action caterpillars take when infected with the virus. Overall, I found that viral infection and diet simultaneously impact the lepidopteran immune response and influence the life history tradeoffs in V. cardui.