Fig. 1 Brood treatment, stage and
appearance. (a) Showing one side of a
whole brood comb within a mediumdepth
Langstroth frame (perimeter of
frame not shown) immediately after the
area in the red circle had been treated
with liquid nitrogen. Also visible is the
temporary wire grid that was placed
above the tested frame, to facilitate the
relocalization of the cells at both time
points. (b) Showing patches of cells
from (a). The centre cell in each patch
is an example of one of the 4 brood
age/stage categories used: I- egg,
II- young larva in open cell, III- older
larva in open cell, IV- capped cell
containing a larva or pupa. The lower
photograph shows the same patches
48 h later; (c) Showing the patch of
cells treated with liquid nitrogen
immediately after (above) treatment
and 48 h later (below). The circular
black line in the upper photograph is
the mark left by the metal cylinder that
was pushed into the brood to contain
the liquid nitrogen. It can be seen that
the effect of the treatment is
concentrated within the circle and
extends in a band 1–3 cells wide
around the circumference.