Storage of Oxalic Acid Sucrose Solution

Stefan Bogdanov, Verena Kilchenmann, Jean-Daniel Chamere, Anton Imdorf
Swiss Bee Research Centre
Dairy Research Station, Liebefeld. CH-3003 Bern

The alternative treatment concept against Varroa destructor suggests one treatment with oxalic acid in late autumn, as soon as the colonies are free of brood. Oxalic acid can be sprayed (30 g oxalic acid dihydrate in one litre water, Imdorf et al., 1995) (or trickled (35 g oxalic acid dihydrate in one litre sucrose solution, proportion 1:1, Chamere et al., 2001)
Many beekeepers noticed that the oxalic acid sucrose solution used for trickling changes its colour to brown after prolonged storage at room temperature. Analysis of the coloured solution indicated a great increase of the hydroxymethylfurfural (HMF) content. This is the substance used to detect a loss of quality in overheated honey. Sucrose solution with a high HMF content is toxic to bees (Jachimowrtz and El., 1975).
In a laboratory trial we investigated the influence of various storage conditions on the increase of the HMF content in oxalic acid sucrose solutions.

Storage conditions

• Room temperature with daylight
• Room temperature without daylight
• Storage in the dark at 15°C
• Refrigerator at 4°C
• Deep freezer at -20°C

Analysis

The solution tested contained 60 g oxalic acid dihydrate in one litre of syrup (1:1). The HMF content in the neutralised solution (pH between 5 and 7) was analysed by the photometry method according to White (Bogdanov et al., 1997) at regular intervals during 57 weeks (Fig. 1).

Results and Discussion

The storage temperature has a great effect on the formation of HMF already after a few weeks storage. At room temperature, there is a great increase of the HMF content. Daylight has no influence on the formation of HMF. The production of HMF was reduced a lot during storage at 15°C. Storage at 4°C or below seems ideal: no HMF production was noticed under these conditions (see fig. 1)
Oxalic acid causes the formation of HMF as well as other degradation products of sucrose which are the reason for the brown colour of the stored oxalic acid solutions (fig. 2).
Oxalic acid was stable during the entire test period. There is no decrease of concentration, and thus no decrease of efficacy is expected. It is not known, whether the HMF content of oxalic add sucrose solutions stored during a long time has a detrimental effect on bees, when bees are treated against varroa.
Therefore, we recommend as a precaution the use of freshly prepared solutions or solutions stored in a refrigerator. The solution can be stored during maximum 6 months at a storage temperature of 15°C.

Storage of oxalic acid-sugar solution

Fig. 1: Influence of storage of oxalic acid sucrose solution on HMF content.

Fig. 2: Change in colour of oxalic acid sucrose solutions at various storing conditions during 57 weeks.

After Bogdanov S. Kilchenman V., Chamere J.D., Imdorf A. (2001) Comment et combien de temps pout-on conserverles solutions sucrees d'acide oxalique? RSA 98 (7) 303-305

Note: After our publication another work on the storage of oxalic acid in sucrose solution was published (Prandun et al., 2001 ). The results and the conclusions of this work are similar to ours.

Translation: Barbara Bogdanov

References

Bogdanov S., Martin P., Lullmann C., Harmonised methods of the European honey commission, Apidologie (extra issue) (1997) 1-59.

Bogdanov S., Kilchenman V., Chamere J.D.. Imdorf A. (2001) Comment et combien de temps peut-on conserver les solutions sucrees d'acide oxalique? RSA 98 (7) 303-305.

Chamere J.D., Imdorf A., Traufelbehandlung mit Oxalsaure: Versuche 1999/2000 und Andwendungsempfehlungen fur Mitteleuropa. Schweiz Bienen-Zeitung 124 (1) (2001) 18-22.

Imdorf A., Chamere J.D.. Bachofen B. Wann ist die Oxalsaure ais Varroazid geeignet?. Schweiz Bienen-Zeitung 118 (7) (1995) 389-391.

Jachimowicz T., El S.G., Zur Problematik der Verwendung von Invertzucker fur die Bienenfutterung. Apidologie 6 (2) (1975) 121-143.

Prandin, L, Dainese, N., Girardi, B., Damolin, 0.. Piro, R., Mutinelli, F. A scientific note on long-term stability of a home-made oxalic add water sugar solution for controlling varroosis Apidologie, 32(5)451-452.

Swiss Bee Research Centre (2001)