COS 302-2 - Virus on the landscape: Monitoring the effects of population density and host plant use on viral prevalence in wild Euphydryas phaeton

Abstract: Host range expansions by phytophagous insects are an inevitable response to a changing
environment due to habitat destruction, fragmentation, invasive species, and shifting species
ranges. The introduction of an exotic plant (Plantago lanceolata) into the habitat of a native
butterfly (Euphydryas phaeton) has led to an expansion by E. phaeton from its native host
plants which include Chelone glabra. In many parts of its range, the expansion to the exotic
plant has allowed E. phaeton to persist where the native plant has been extirpated. The native
host plant grows in patchy stands in wetlands, whereas the exotic host plant tends to be
distributed throughout, and along the margins of, frequently disturbed areas. These distinct
growth patterns and habitat requirements have consequences for the populations of
caterpillars using them. Additionally, these may in turn have consequences for higher-level
interactions with pathogens that infect E. phaeton. Here, we are interested in exploring spatial
distributions of host plants, as well as host plant chemistry, on the prevalence and distributions
of a pathogen in these populations of E. phaeton. To examine the role of spatial and host plant
factors on pathogen prevalence and distributions at a landscape scale in E. phaeton, we
conducted surveys at six sites across New England throughout the summer of 2021. We
collected E. phaeton at three life stages, measured host plant locations, densities, and
identities, and collected leaf samples from host plants for chemical analysis. All collected E.
phaeton were screened for Junonia coenia densovirus (JcDV) using quantitative PCR. We will use
these data to address whether caterpillar densities (caterpillars per plot), proximity to
other groups of caterpillars, host plant density or identity (native vs exotic), and host plant
chemistry (concentrations of defensive compounds) are drivers of viral prevalence in wild
populations. So far, we have found significant differences in viral prevalence by site, where a site with highly clustered caterpillars on the native host plant has very high disease prevalence. Ultimately, with a better understanding of the
distribution of pathogens at the landscape scale, and the effects of host plants on these
pathogens, we hope to enhance the current understanding of the impact of spatial and host
plant factors in disease dynamics which may ultimately have consequences for insect
populations.