Serial measurement arrangement

Serial plumbing has the advantage that during differential measurement of CO2 production or O2 consumption both the measurement and the reference parts of the sensor devices always are operated at exactly the same flow rate. It is also cheaper than a parallel setup (see section because only one mass flow controller is needed (Lighton, 2008; Stabentheiner et al., 2012).

1. Air supply: Fresh air should be taken from outside the laboratory via a tube to avoid disturbance of the measurements by air exhaled by the experimenters. The delay between the reference and measurement tubes or detectors of the measurement devices may otherwise lead to unnecessary baseline fluctuations. To additionally dampen fluctuations in outside air CO2 or O2 content, the air should be passed through a buffer container (5-10 l). An alternative is air from a compressed-air bottle.

2. Pumps: A pump feeds the air to a drying unit [e.g. Drierite columns (see safety advice in, or a cool trap regulated at a low temperature of 2–10 °C], which brings the water content of the air to zero or a low and constant level. Regulated pumps are of advantage because they help to avoid unnecessary overpressures in the system (offered, for example, by Sable Systems International).

3. Mass flow regulation: Subsequently, the air has to pass a mass flow controller (e.g. Brooks 5850S, Brooks Instruments; or Side Trak 840-L, Sierra Instruments; etc.). A range of 0–1000 ml/min is suitable for investigating both resting end endothermic honey bees. A small range mass flow controller of 0–100 ml/min may be recommended to improve accuracy of flow regulation for measurements of tiny honey bee larvae which may weigh considerably less than 1 mg in early stages of development (Petz et al., 2004).

4. Measurement: The air then has to pass the reference sensor of the differential gas analyser. Afterwards, the air is put through the measurement (respirometer) chamber containing the honey bee (see section Before the air is forwarded to the measurement sensor it has to be dried again (and in the same way as the reference air stream).