Nosema ceranae parasitism impacts olfactory learning and memory and neurochemistry in honey bees (Apis mellifera)

Nosema sp. is an internal parasite of the honey bee, Apis mellifera, and one of the leading contributors to colony losses worldwide. This parasite is found in the honey bee midgut and has profound consequences for the host’s physiology. Nosema sp. impairs foraging performance in honey bees, yet, it is unclear whether this parasite affects the bee’s neurobiology. In this study, we examined whether Nosema sp. affects odor learning and memory and whether the brains of parasitized bees show differences in amino acids and biogenic amines. We took newly emerged bees and fed them with Nosema ceranae. At approximate nurse and forager ages, we employed an odor-associative conditioning assay using the proboscis extension reflex and two bioanalytical techniques to measure changes in brain chemistry. We found that nurse-aged bees infected with N. ceranae significantly outperformed controls in odor learning and memory, suggestive of precocious foraging, but by forager age, infected bees showed deficits in learning and memory. We also detected significant differences in amino acid concentrations, some of which were age specific, as well as altered serotonin, octopamine, dopamine and L-dopa concentrations in the brains of parasitized bees. These findings suggest that N. ceranae infection affects honey bee neurobiology and may compromise behavioral tasks. These results yield new insight into the host-parasite dynamic of honey bees and N. ceranae, as well as the neurochemistry of odor learning and memory under normal and parasitic conditions.