An Explanation Of Discoidal Shift In Honey Bees
Soon after I joined BIBBA (VBBA) in 1964 Beowulf Cooper sent me a report on a sample of
my bees. In this report he mentioned cubital index (CI) and discoidal index (DI). I enquired
of him regarding these indices. He told me that DI was described in a paper by Louis.
I also found a brief description of CI in the chapter by Professor Ruttner in "The
Hive and the Honeybee" edited by Grout. I obtained a copy of the paper by Louis
from IBRA. Since the text was in French I was unable to read it, but the diagrams and
graphs gave me sufficient information to understand how to make the measurements and
their significance in identifying native honeybees. Louis and Cooper measured DI simply
as negative, zero or positive. I borrowed a low power microscope with a cross graticule
and a measuring device which enabled me to make the necessary measurements of wings
mounted on a microscope slide. A little time later I realised that I could mount the
wings in a 35 mm glass slide binder and project them onto a wall. I drew a 'T' shape on
a piece of paper to measure DI and measured the length in millimetres of the two cubital
veins to produce the CI. I found that the DI of my bees was more negative than the bees
that Louis had measured in France. I also noticed that the position of the discoidal point
varied considerably. With this discovery I began to record DI as slightly, moderately
or strongly negative or positive and again, after a while, I realised that these
differences could be measured precisely in degrees. Now that I could put a figure
on both CI and DI I used my experience of teaching "modern" maths to eleven
year old children to devise a scattergram. The distinctive patterns that were produced
were quite exciting at the time. Although I told other local beekeepers about my studies,
the work was done entirely for my own interest with no thought of publication.
In 1981 the Rev. Eric Milner, a friend of my aunt since his schooldays, visited me.
He had recently attended the BIBBA Conference at Celle in Germany where he had heard
about honeybee morphometry. He knew that I had been doing similar work and wanted
to know more about it. I told him all that I knew and added that there was much more
to learn, but all the information was in German or French. He offered to obtain papers
from IBRA and translate them in which task he was later joined by his brother Ashleigh.
One of the early papers was by Goetze describing Discoidal Verschiebung. This latter
word was translated by the Milner brothers as "displacement" or "shift",
a word in common use in Yorkshire with several meanings, one of which was "to move
an object". Since that time we have used the term "Discoidal Shift" (DS).
Goetze used a small magnifying glass to measure DS. This was of the kind normally used
to measure the number of threads in fabric, having a grid divided into 0.1 mm squares.
I was unable to obtain one of these, so continued to measure DS in degrees.
Professor Ruttner accepted the measurement of DS in degrees and the scattergram of CI and
DS as useful aids in "The Dark European Honeybee" and in his last book to
be published "Naturgeschichte der Honigbienen".
John E Dews
28th October 2002