Baculovirus infection, host immunity and pathogen competition in the cabbage looper, Trichoplusia ni

Competition between pathogens within a host could change the short term and evolutionary outcomes of an infection. These interactions include resource-based and immune-mediated competition. We understand little about the insect immune response to virus infection and how this alters the host for future co-infecting pathogens. I characterised several immune parameters of the cabbage looper, Trichoplusia ni, in response to challenge by a baculovirus, TnSNPV, and found that all parameters reduced with increasing virus dose. To measure the effect of competing pathogens on virus success, I exposed T. ni to TnSNPV followed by either the bacterium, Bacillus thuringiensis, or the fungus, Beauvaria bassiana. The fungus reduced the infection success of the baculovirus and the bacterium negatively impacted virus replication. This outcome has consequences for microbial control agents in insect pest management and adds to our fundamental understanding of the effect of mixed infections on pathogen and host populations.