Implications
On a practical level, this work has a depressing conclusion: more work is required, even to verify what we think we know now about fly immunity.
It is clearly critical to measure infection burdens, not just health outcomes, so that it is possible to analyse both the intensity-dependent health outcome, and variance in health outcome that is over and above that due to infection intensities.
Worse, it is not possible to assume that a particular gene is uninvolved in defense based on experiments with a single pathogen, or even a limited number.
A panel of pathogens, and hence much larger experiments, are required.