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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 1.21 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 10.2mPas (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. [ABSTRACT FROM AUTHOR]

To test whether variation in muscle efficiency contributes to thermal stability during flight in the orchid bee, Euglossa imperialis, we measured CO2 production, heat loss and flight kinematics at different air temperatures (Ta). We also examined the relationship between wingbeat frequency (WBF) and Ta in five additional species of orchid bees. Mean thoracic temperature (Tth) for Eg. imperialis hovering in a screened insectary and in the field was 39.3±0.77° C (mean ± 95% C.I.), and the slope of Tth on Ta was 0.57. Head and abdominal temperature excess ratios declined with Ta, indicating that Eg. imperialis were not increasing heat dissipation from the thorax at high Ta. Elevation of Tth above Ta was correlated with WBF, but Tth alone was not. Estimates of heat production from both respirometry and heat loss experiments decreased 33% as Ta rose from 24 to 34°C. Mean muscle efficiency over this temperature range was 18% assuming perfect elastic energy storage and 22% assuming zero elastic energy storage. Both efficiency estimates increased significantly as Ta rose from 24 to 34°C. In all six species examined, WBF declined significantly with Ta. These data indicate that hovering orchid bees regulate heat production through changes in wingbeat kinematics and consequent changes in energy conversion by the flight motor. Temperature-dependent variation in elastic energy storage or muscle contraction efficiency or both may contribute to the observed trends. [ABSTRACT FROM AUTHOR]