Stress decreases pollen foraging performance in honeybees.

For honeybees, foraging is energetically demanding. Here we examined whether stressors, which increase metabolic demands, can impair foraging performance. A controlled non-pathogenic stressor (immune challenge) resulted in a change in foraging preferences of bees. It reduced pollen foraging, and increased the duration of trips in pollen foragers. Stress also reduced the amount of octopamine in the brain of pollen foragers (a biogenic amine involved in the regulation of foraging and flight behaviour in insects). According to the literature, flight metabolic rate is higher during pollen foraging than nectar foraging, and nectar gives a higher energetic return relative to the foraging effort when compared to pollen. We thus propose that stress might be particularly detrimental to the performance of pollen foragers, and stressed bees prefer the energy-rich resource of nectar. In conclusion, stress, even at low levels, could have consequences on both bee foraging behaviour and thereby the nutritional balance of the colony.