The damage threshold hypothesis and the immune strategies of insects

The insect immune response strategy has generally been considered bipolar: either resistance or death. Lately, a much broader and subtler landscape has emerged: occurrence of tolerance and resistance has been described as a host-regulated immune response. However, little is known about the interplay between the immune response strategy mounted by the insect during infection and the damage produced by the pathogen. Based on the Matzinger model of danger/damage, we propose a quantitative model to explain the occurrence of either resistance or tolerance. We discuss the features to be analyzed and describe the terms of reference by which, with basic models, we distinguish between immune strategies. Pathogen type and mixed infections are also contemplated. We hope this analysis will give new perspective, from an evolutionary ecology standpoint, on immune response measurements in the context of insect infection, and on the importance of (non-self or self) damage.