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Date: | Tue, 15 Mar 2022 16:28:39 -0400 |
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I had a question on the very useful metabolic rate curve drawn by Southwick. It was re-drawn by Dr Melathopoulos in some CAPA Wintering literature. I was just reviewing Southwick 1982 (1) on the explanation on the right hand side of the curve (10C to 20C) range. I was looking for the reasoning behind this large increase.
"Colonies containing brood showed less excursion in metabolic rate resulting from the higher minima
maintained at night (cf. Fig. l(b). Between 10 and 20’ C, colonies containing capped brood showed an
average of 42.4 + 3% (11 = 14) reduction in metabolism at night (I 5 min minimum) as compared to the
day (15 min maximum). Without brood. colonies reduced metabolic rate at night as compared to day-
time values by 78.7 & 1.7%,(n = 9). "
"Nevertheless, certain trends found via CO2 measurements support my results. I found, for example. that at temperatures of 10-20C the cluster readily breaks in the daytime resulting in very high metabolic rates combined with very low rates at night." - Maybe our longer darker winters work to the bees advantage in the far north.
The above comment aligns with my hypothesis that a broodless colony will have much lower metabolic rates than that of a fully brooded colony (up to 78.7% lower MR). The three described scenarios also re-enforces the concept of cluster driven vs enclosure driven. The higher MR is due to the need to maintain brood nest Ts. The second quote also supports my idea. A colony with or without brood, breaking cluster will lose significantly more heat in a wooden enclosure and require to up their MR to maintain their set point ~18-20C for broodless, ~30C capped brood and 35C for eggs to capped brood.
So Frank, a top insulated colony would therefore have a lower MR than a colony without top insulation as more residual heat would be conserved.
The curve is miss-leading and folks have assumed (me included) that bees have higher Metabolic rates at Ts above 10C. They do if brood is present in un-insulated boxes.
On a side note: The air going into the test colonies was dried
"The out-side air was first drawn through Drierite (CaSO4) to remove water, passed through 1m of copper tubing within the temperature cabinet for temperature equilibration and then through the hive."
It would be interesting to know if they also measured humidity levels in test hives. i.e. -20C RH60% air has 1g/m3 and 20C RH60% air has 10g/m3. A colony seems to target 15-18 g/m3 (winter-broodless) and 25-30 g/m3 (with brood). How much of the metabolic rate is actually about moisture levels and how much is about keeping warm?
Reference:
(1) Metabolic energy of intact honey bee colonies
(https://vdocuments.mx/metabolic-energy-of-intact-honey-bee-colonies.html?page=3
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