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First published online December 1, 2006
Journal of Experimental Biology 209, 4901-4907 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02593
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Mechanics of nectar feeding in the orchid bee Euglossa imperialis: pressure, viscosity and flow

Brendan J. Borrell

Department of Integrative Biology, University of California, Berkeley, CA 94720-3140, USA

e-mail: bborrell{at}cal.berkeley.edu

Accepted 16 October 2006

The orchid bee Euglossa imperialis sucks nectars through a slender proboscis. I tested how nectar properties influence this suction pressure and whether ambient air pressure sets the upper limit for suction feeding. Nectar intake rate was measured as a function of sucrose concentration (5-75% w/w), nectar viscosity (2-80 mPa s), and ambient pressure (101-40 kPa). Intake rate declines from about 1.2 µl s-1 to 0.003 µl s-1 as sucrose concentration increases from 15% to 65% sucrose. When sucrose concentration is held at 25% while viscosity increases from 2 to 80 mPa s, intake rate declines. When viscosity is held at 10.2 mPa s (the viscosity of 50% sucrose) while sucrose concentration increases from 5% to 50%, intake rate remains constant. Intake rate was limited by a reduction in ambient pressure at all nectar concentrations. Assuming a rigid proboscis, the Hagen-Poiseuille equation suggests that suction pressure increases with viscosity from 10 kPa at 5% sucrose to 45 kPa at 65% sucrose. However, because intake rate declined by the same fraction under hypobaria (40 kPa) at all sucrose concentrations, the euglossine bee proboscis may be better described as a collapsible tube: expanding or collapsing depending on the flow rate, the pressure gradient along the proboscis, and circumferential forces imposed by the proboscis walls.

Key words: Apidae, Euglossini, foraging, energetics, biomechanics, tongue


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