Plant-insect-entomopathogen interactions: Do host plants have a role in the outcome of mixed pathogen infection and successful pathogen transmission?

Plants play a major role in insect-pathogen interactions. Differences in plant quality can impact insect growth and condition, which can affect susceptibility to pathogens. Insects are also commonly challenged by multiple pathogen species, yet little is known about how nutrition affects the outcome of mixed pathogen infections. Additionally, traits that enable pathogens to be good competitors within the host might not be the same as those needed for transmission. Our earlier work has shown that host nutrition significantly affects host survival to infection and within-host pathogen replication, but the outcome varies with pathogen type.

In a spray assay, using Trichoplusia ni (cabbage looper), its nucleopolyhedrovirus (TnSNPV) and the entomopathogenic fungus, Beauveria bassiana, we asked whether host plant (broccoli/tomato) and mixed infection could alter pathogen efficacy in controlling the cabbage looper. We then measured pathogen transmission, challenging T.ni larvae with either a single pathogen, two pathogens simultaneously or asynchronously and transferring challenged larvae onto caged host plant before death. Twenty healthy larvae were then added to each plant. Using destructive samplings, collected larvae were reared on artificial diet until death or pupation to estimate pathogen transmission.

We hypothesized that host plant architecture, plant secondary chemicals; spatial structure of pathogen transmission stages, and temperature and humidity play a major role in insect-entomopathogen interactions in the field. The results showed that the host's likelihood of being infected depends on the host plant and pathogen infection pathway. The results presented give insight into the complex interactions that can modulate pathogen transmission in the field.