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Inside JEB |
ON A POLLEN HIGH
kathryn{at}biologists.com
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When bees return from successful foraging trips, a well-laden insect can carry as much as 80% of its own body weight. But how much effort the insects put into this daily Herculean task wasn't clear, until Erica Feuerbacher and Jon Harrison began putting hovering bees through their paces. Measuring the labouring insect's metabolic rate and temperature, as well as they way they beat their wings, Feuerbacher compared the insects' metabolism as they hovered carrying loads of pollen, and nectar. Amazingly, the type of cargo that the insects carried had a dramatic effect on their metabolic rate, with pollen carriers working 10% harder then the insects that filled up on nectar (p. 1855). Harrison explains that this could be for a number of physiological reasons, which allow pollen foragers to capitalise on pollen as a rich energy source at any time of day.
Feuerbacher also wondered whether the insects laboured more under heavier loads, so she began increasing the weight that the insect's carried. Surprisingly, their hovering metabolic rate only rose by a small fraction. So how were they able to lift weights that were a significant proportion of their body weight with little extra effort? Feuerbacher and Harrison think that the insects resort to `unsteady power-generating mechanisms' to give them the extra lift they need to keep them, and their load, aloft.
References
Feuerbacher, E., Fewell, J. H., Roberts, S. P., Smith, E. F. and
Harrison, J. F. (2003). Effects of load type (pollen or
nectar) and load mass on hovering metabolic rate and mechanical power output
in the honey bee Apis mellifera. J. Exp. Biol.
206,1855
-1865.
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