Comparison of Spray or Trickle Oxalic Acid Treatment
Translated by A.E. McArthur MIL from the Schweizerische Bienen Zeitung March ‘99, pages 141 – 143
During November 1998 when the colonies had virtually no brood 17 colonies were treated using oxalic acid- dihydrate and monitored every day over a period of 50 days for mite fall.
Five colonies were treated using the spray technique. Each bee covered comb side was sprayed with 3ml of solution. (30g oxalic acid dihydrate : 1 litre of water). Two sets each of six colonies were treated with 3 - 4ml of solution trickled into each space between combs containing bees, one set of six treated using a 3.2% and the other six using a 1.88% solution of oxalic acid in a 1 : 1 sugar solution at hand heat.
All of these treatments produced the same Varroa reducing effect. According to statistic analysis they did not differ. The effectiveness of the treatment can continue over a period of more than two months, and for this reason should only be used once in winter. Additional measures like two or three cycles of drone sacrifice in the Spring as well as the setting up of nucleus stocks and shook swarms which can be treated for Varroa should be carried out. Strict monitoring of all colonies over a period of days at different times of the year to check for re-invasion should be carried out in order to maintain the Varroa populations under the critical level.
Making Up the Solutions
-30 g oxalic acid dihydrate dissolved in one litre of water (OxS 3%)
-50 g Oxalic acid dihydrate in a sugar solution ( a kilogram of sugar is dissolved in a litre of water – this corresponds to a 3.2% solution) (OxT 3.2%)
-30 g oxalic acid dihydrate in a sugar solution ( a kilogram of sugar is dissolved in a litre of water – this corresponds to a 1.88% solution) (OxT 1.88%)
When using the spray method a face mask and rubber gloves must be worn. With the trickle method rubber gloves and protective glasses are sufficient.
Oxalic acid dihydrate may be obtained in a chemist shop. A made up solution can be obtained from the firm Andermatt Biocontrol AG.
This work was carried out in order to establish an effective concentration of oxalic acid which gives a satisfactory mite kill.
Reduced Oxalic Acid Concentration
After colonies have been treated in August/September with formic acid the individual colonies should be monitored for mite fall in October/November over a period of seven to ten days. Where a mite fall of greater than one mite per day occurs the colonies must be given an additional treatment. An effective but labour intensive method is the spraying of oxalic acid onto each bee covered comb. Trickling oxalic acid in a sugar solution into the spaces between the frame occupied by bees is less labour intensive and it is not necessary to remove the frames from the hives. The initial 12.5% acid concentration was discovered to be to powerful. I treated with this concentration and lost 3 colonies. The remaining 14 colonies produced comparable honey yields in the summer of 1998 to the colonies which were not treated with oxalic acid.