Abstract:
Host-pathogen coevolution leads to reciprocal adaptations, allowing pathogens to increase
host exploitation or hosts to minimise costs of infection. As pathogen resistance is often
associated with considerable costs, tolerance may be an evolutionary alternative. Here, we
examined the effect of two closely related and highly host dependent intracellular gut
pathogens, Nosema apis and Nosema ceranae, on the energetic state in Nosema tolerant and
sensitive honeybees facing the infection. We quantified the three major haemolymph
carbohydrates fructose, glucose, and trehalose using high-performance liquid
chromatography (HPLC) as a measure for host energetic state. Trehalose levels in the
haemolymph were negatively associated with N. apis infection intensity and with N. ceranae
infection regardless of the infection intensity in sensitive honeybees. Nevertheless, there was
no such association in Nosema spp. infected tolerant honeybees. These findings suggest that
energy availability in tolerant honeybees was not compromised by the infection. This result
obtained at the individual level may also have implications at the colony level where workers
in spite of a Nosema infection can still perform as well as healthy bees, maintaining colony
efficiency and productivity.
