Figure 2.

Proposed model for how Nosema infection impacts worker metabolism, hormonal signaling and immunity. 1) Infection with Nosema may directly trigger expression of immune genes independent from worker behavioral state, 2) Infection with Nosema may damage nurse midgut tissue and retard midgut development, resulting in reduced nutrient uptake. Poor nutrition may be compounded by energetic costs exerted by Nosema parasites. Increased worker metabolic costs may alter worker genes regulating hormones and stress response to dietary restriction. Changes in expression of these genes may accelerate worker behavioral maturation, driving them towards a foraging state, which in turn alters worker immune state. 3) Nosema parasites may directly alter expression of genes regulating behavioral maturation, driving workers towards a foraging state with associated changes in immune function. These hypotheses are not mutually exclusive.