6.1.7. Closed chamber method (CO2 accumulation)
With honey bee eggs, flow through respirometry is not directly applicable, but this can be done with a closed chamber method. In a protocol described by Mackasmiel and Fell (2000), a measurement chamber (e.g. 2 ml autosampler vials) containing one egg on a piece of cell base wax is closed for some time (e.g. 12–14 h) to accumulate the CO2 produced by the eggs. After certain periods, air samples of 250 µl are drawn from the vials and injected into an infrared gas analyser (IRGA). Accuracy of egg respiration measurement is ascertained by comparison with the air of empty vials and with the air of vials containing dead eggs (frozen overnight) or containing just a piece of cell base wax (Mackasmiel and Fell, 2000). To achieve a high accuracy of CO2 measurement, the IRGA should be flushed with air deprived of CO2 by pumping it through a calcium carbonate container. CO2 can also be scrubbed with Mg(ClO4)2, or Ascarite (but see User Safety Advice for these substances in section 220.127.116.11.). It is also possible to consider a setup where the chamber is inserted in the gas path of a DIRGA and CO2 accumulation is accomplished by closing magnetic valves for appropriate periods.