First published online October 27, 2003
Hot bees in empty broodnest cells: heating from within
Marco Kleinhenz1,*,
Brigitte Bujok1,
Stefan Fuchs2 and
Jürgen Tautz1
1 Beegroup Würzburg, Lehrstuhl für Verhaltensphysiologie und
Soziobiologie, Universität Am Hubland, D-97074 Würzburg,
Germany
2 Institut für Bienenkunde (Polytechnische Gesellschaft), FB Biologie
der J. W. Goethe-Universität Frankfurt am Main, Karl-von-Frisch-Weg 2,
D-61440 Oberursel, Germany
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Fig. 1. Observation hive with three comb pieces (A, B, C), allowing thermographic
temperature measurements of bees inside observation cells. Comb cells in the
background are indicated but could not be seen during the observations. The
comb chamber was covered with infrared transparent film. The smaller chamber
was half filled with sugar dough and contained the queen (Q) in a cage.
Insulation covering the hive (4 cm polystyrene walls on all sides; not shown)
was partially removed while the observations were being made. Hive temperature
(Thive) was measured with a thermistor (T) inside a
plastic tube.
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Fig. 2. Close-up thermographic recordings of bees inside three empty cells adjacent
to brood cells. A and B show a view of the same cells at different times. x, y
and z each indicate the bottom of one of the observation cells. The white
lines indicate the middle wall. (A) Three heating bees with different thorax
temperatures (Tth); all of them are seen from their dorsal
sides. (B) A resting bee in cell y and a heating bee in cell z (turned
upside-down). Cell x is empty. Abbreviations: abd, abdomen; hd, head; th,
thorax; w, wing. Asterisks mark the wax walls of two sealed pupae cells
adjacent to the observation cells. The temperatures refer to the bee
thorax.
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Fig. 3. Simulation of worker heating with an artificially heated thorax (setup C).
The cross-section shows one side of a comb. In different cycles, the thorax
was placed inside an empty cell (variation A) or on the comb surface either
touching the cap (variation B: d=0 mm) or at a distance of
1.0–1.5 mm from the brood cap (variation C). The locations of
thermistors for measurement of thorax temperature (Tth),
cap temperature (Tcap) and brood temperature
(Tbrood) are indicated. Other than shown, the
Tcap thermistors were not introduced from brood cell #2
but from adjacent cells in the background that were not used for temperature
measurements. Abbreviations: d, distance; m, middle wall of the comb;
R, resistor inside an isolated bee thorax.
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Fig. 5. Thermogram of worker bees in the brood area, as seen in a common
observation hive. The sealed area appears grey with no further details in this
image; open cells are identifiable by the hexagonal structure of the cell
rims. One bee with heated thorax [A;
Tth(entry)=37.9°C] is about to enter an open cell
adjacent to three sealed brood cells and pokes its head and the anterior part
of its thorax into the cell (the dark structure on the heated thorax is the
scutellum, seen from posterior-dorsal). Worker bee B has just left the open
cell in the centre of the image [Tth(exit)=37.3°C].
The view on cell visitors C and D is partly hidden by bees on the comb
surface. The onset of heat production during cell visits is roughly indicated
when the cell interior and thorax (visible as a ring-like structure around the
dark silhouette of the cool abdomen) start `glowing' with increasing
intensity. Note the different intensities caused by cell visitors E and F.
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Fig. 4. Thorax temperatures (Tth) of three different honeybees
in the sealed brood area on the comb surface. (A) A 2 min warm-up (+4.7°C)
prior to a cell visit provides a Tth(entry) of 39.4°C.
(B) Heat production during a cell visit is revealed by a net warming, with
( Tth)net=+4.1°C. Heating was not
resumed during a subsequent short-duration visit (0.7 min) to the same cell.
(C) Repeated warmings prior to consecutive cell visits. Asterisks mark periods
of 30 s or longer during which the bee's thorax was hidden by another bee and
no temperature measurements could be made.
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Fig. 7. Diagram of respiratory pumping movements of the abdomen of bees inside
cells. Pumping movements are drawn as spikes from 0 to 1 at the time of
occurrence. (A) Resting bee with
Tth=33.4±0.3°C. Thick lines are bursts of
several pumping movements, which are shown at a higher temporal resolution in
B. (C) Heating bee with Tth=36.4±0.3°C. Note
that the time-scale of A is different from that of B and C.
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© The Company of Biologists Ltd 2003
, bee enters
cell; 
, bee leaves cell. Tth of bee outside cell
(open circles) and inside cell (filled circles) are plotted.
36°C entered an empty cell adjacent to this brood cell for a
long-duration cell visit (