This study evaluates the effect of the long-term nutritional state of bumblebee field colonies on forager activity. Foraging for pollen and nectar is necessary for bumblebees as colony development depends on the amount of resources gathered. However, foraging is risky and costly: for instance, worker longevity is inversely related to foraging effort. Given this tradeoff, workers from colonies with abundant food supplies could either maintain foraging to increase reserves for future use or forage less to avoid risks. We tested these hypotheses by measuring with motion detectors the foraging activity rate in four field colonies of Bombus impatiens at the onset of the production of sexuals, two of which were fed a sucrose solution ad libitum and pollen at regular intervals throughout the summer. Feeding colonies significantly reduced their foraging activity rate by 22% ± 13% (SD) which supports the hypothesis that workers prefer to avoid risks. Decreased activity was most evident early in the morning and at the end of the day. Reduced activity at these times could be energy saving strategies to avoid flight at colder temperatures and during periods of high competition for resources.
Species 1: Hymenoptera Apidae Bombus impatiens (bumble bee)
Keywords: foraging activity, colony nutritional state
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