Contrasting transmission strategies, host dynamics, and pathogen dynamics in simple insect-pathogen communities

Insect baculovirus infections exhibit both horizontal and vertical transmission strategies. Horizontally transmitted overt infections require the death of the host, while vertically transmitted asymptomatic covert infections rely on hosts surviving and transmitting the infection to their offspring. Ecological conditions may determine the optimum balance between modes of transmission and although there is much theory, there are no experimental investigations into the relationship between environment, host population dynamics and pathogen transmission strategy. To address this we set up replicated microcosm communities using a well-characterized model system comprised of the Indian meal moth (Plodia interpunctella) and its baculovirus (PiGV), which can transmit both vertically and horizontally. We established communities with and without PiGV, and we manipulated the environmental quality, which is a major influence on host dynamics, by providing nutrient-rich or nutrient-poor food sources. We hypothesised that overt infection would be favoured over covert infection in the high quality environment, and the balance would shift in favour of covert infection in the poor quality environment.. We collected age-structured host data and overt infection data from the communities that included PiGV and those without and we measured the level of covert PiGV infection in adults sampled from the populations every three host generations. I present host dynamics and overt and covert pathogen prevalence, and I discuss them in the context of contrasting pathogen transmission strategies and environmental quality.