Does parasitic infection impair the ability of bumblebees to learn flower-handling techniques?

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Although the capacity to learn how to manipulate flowers plays an integral role in the foraging of bumblebees, little is known about the effects of parasitic infection on the motor learning and memory of host bees. In the laboratory experiment reported here, we examined whether infection by the intestinal protozoan Crithidia bombi affected the ability of bumblebees, Bombus impatiens, to learn the specialized motor pattern required to handle a novel flower type. Using videotaped records of foraging behaviour, we related the motor performance of bees to the intensity of C. bombi infection. Low intensities of infection had no effect on the ability of bees to learn a novel flower-handling method; however, a high intensity of infection significantly reduced both motor-learning rate and maximum handling proficiency. In addition, highly infected bees showed a 200% increase in the amount of time and the number of visits required to learn how to manipulate flowers. These results indicate that C. bombi can influence the foraging behaviour of host bumblebees in subtle but ecologically significant ways.