Our lab uses a tripartite system consisting of three model organisms: an insect, Drosophila melanogaster; the entomopathogenic nematodes Heterorhabditis and Steinernema together with their symbiotic bacteria Photorhabdus and Xenorhabdus. We investigate the molecular basis of insect immunity, bacterial symbiosis/pathogenicity and nematode parasitism, and explore the mechanisms that regulate the complex interactions between these important biological processes. This system promises to reveal not only how pathogens evolve virulence but also how two pathogens can come together to exploit a common host.