An Explanation Of Discoidal Shift In Honey Bees

Discoidal Shift

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

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