In an excellent two-part article published in the December 2023 and January
2024 ABJ respectively entitled ‘Thermoregulation in Honey Bees’, the author
(Frederic Eggers de Villepin) makes the following observation arising from a
paper that has been recently referred to here on the pages of Bee-L, namely:
‘Endothermic heat production in honeybee winter clusters’ -
https://journals.biologists.com/jeb/article/206/2/353/13914/Endothermic-heat
-production-in-honeybee-winter
‘The study also reveals a little known behavior: Endothermic bees
periodically pass through the cluster, visiting its outermost layer, only to
re-enter a few seconds later. It is assumed that it is these bees that play
a role in regulating cluster temperature, as it seems that it is the
temperature of the mantle and not the temperature of the cluster center that
guides the heat production effort (Stabentheiner et al., 2021), since this
is where the bees closest to the lethal level are located.’
This observation is based on the following from the research:
‘Additional (and conclusive) evidence that there is always a certain number
of endothermic bees inside a broodless winter cluster at air temperatures
around the freezing point was provided by the experiment where the cluster
surface was thermographed continuously for many hours. Evaluation of 21 h of
recordings from night-time (21:00 h-08:00 h) showed that bees appeared on
the cluster surface at a rate of 6-80 bees h-1. All of them were
endothermic, with a mean Thead of 21.6±3.58°C,a Tthorax of 27.5±4.09°C and a
Tabdomen of 20.9±3.62°C (N=1183 values, 781 bees; compare Fig. 1). Of these
bees, 90% re-entered the cluster within 10 s, and the rest re-entered within
3 min. We conclude that visiting the surface by endothermic bees is part of
the natural behaviour in winter clusters.’
But they caution:
‘It should be pointed out that the occurrence of endothermy inside winter
clusters does not contradict the hypothesis of self-organized cluster
thermoregulation (Heinrich, 1981, 1993; Moritz and Southwick, 1992; Watmough
and Camazine, 1995). It is well conceivable that the endothermic bees decide
individually to start shivering thermogenesis or to stay ectothermic.
However, in order to optimize energetic investment, the core bees should
know about the thermal needs of the bees sitting closer to the surface.
Future investigations will have to solve the question of whether or not the
endothermic bees that visit the surface play a role in the regulation of
heat production in winter clusters.’
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