A scientific note on long-term stability of a home-made oxalic acid water sugar solution for controlling varroosis

Abstract

Since the work by Radetzski et al. (1994) on the use of oxalic acid for controlling varroosis, several reports have been published proving the efficacy and tolerability of this organic acid when applied to honeybees (Apis mellifera L.) by spraying or trickling. Tests were carried out by spraying water-diluted oxalic acid (Nanetti et al., 1995) or trickling a solution of oxalic acid, water and sugar (Imdorf et al., 1997;Mutinelli et al., 1997;Nanetti and Stradi, 1997) into colonies during broodless periods. Oxalic acid, water and sugar solutions and the water-diluted oxalic acid (Highes et al., 1999) have occasionally been considered responsible for honeybee losses after treatment, and no data are currently available on their long-term stability. Since such solutions are widely used by beekeepers for controlling varroosis in broodless periods, our aim was to evaluate the characteristics and stability of a homemade oxalic acid, water and sugar solution in various storage conditions, in order to detect modifications of the active ingredients possibly related to toxicity towards honeybees. The homemade oxalic acid/water/sugar solution (OAWS) prepared in the laboratory for the present study is the same as that used for treating beehives against varroosis. It is composed of 100 g oxalic acid dihydrate (Sigma), 1000 g commercial sugar and 1 000 ml drinkable water. The characteristics of water were as follows: pH 7.5, solids 320 mg . L -1 , hardness 27.1 °F, chloride 8.0 mg . L -1 , nitrate 17.5 mg . L -1 , sulphate 21.5 mg . L -1 , iron 5 µg . L -1 . The density of the final solution is 1.236 g . L -1 and the concentration of oxalic acid is 4.2% (0.467 Mol).This solution was stored in 10-ml tubes at various conditions: -20 °C, +4 °C and room temperature (RT) in the dark and in the light. The solution was tested for the following parameters immediately after its preparation: oxalic acid, colour, pH, hydroxymethylfurfural and sugars. The same parameters were determined at 3, 7, 15 and 30 days, and at 2, 3, 4, 5, 6, 7, 8 and 16 months after preparation for each storage condition. Oxalic acid was determined using a commercially available kit (Oxalate Sigma Diagnostics kit, Cat. N. 591-D) adapted for honey (Mutinelli et al., 1997). The colour of the OAWS solution was examined by means of a 2000 Comparator (Lovibond) used for honey colour determination. Hydroxymethylfurfural (HMF) was determined using reverse-phase HPLC equipped with UV detection (Jeuring et al., 1980). Sugars were determined by an HPLC method using a pulsed amperometric detection. This study demonstrated that the concentration of oxalic acid and pH of an OAWS solution topically applied for varroosis control remains constant in all tested storage conditions and over a long period of time, as opposed to changes affecting other parameters (Tab. I). Colour changes observed in samples stored at RT were related to the numerous possible condensation reactions (Maillard reaction), which produce many polycyclic compounds absorbing light in the visible region. The ...

Effectiveness of Different Soft Acaricides against Honey Bee Ectoparasitic Mite Varroa destructor (Acari: Varroidae)

“…Three different oxalic acid concentrations (4.2%, 3.2%, and 2.1%) mixed with sugar syrup were applied as treatments. To attain 4.2%, 3.2%, and 2.1% oxalic acid solutions, 100, 75, and 50 g of oxalic acid dehydrate was mixed with 1 L of sugar water (1:1) [43]. Treatments were applied only to frame spaces that contained bees.…”

Acute Contact Toxicity Test of Oxalic Acid on Honeybees in the Southwestern Zone of Uruguay

“…For these reasons, the study of chemical compounds with miticidal characteristics has become relevant, particularly those chemical compounds normally found in hives or essential oils, such as oxalic acid (OA) (Prandin et al, 2001;Gregorc and Planinc, 2001;Marcangeli et al, 2003, Nanetti et al, 2003Marinelli et al, 2006; SCIENTIFIC NOTE B Rademacher and Harz, 2006;Bacandritsos et al, 2007), formic acid (Calderone, 2000;Bogdanov et al, 2002;Eguaras et al, 2003), and thymol (Imdorf et al, 1995). This type of compounds do not pollute a hive's products (Bogdanov et al, 2002) or produce resistant V. destructor strains.…”

“…This type of compounds do not pollute a hive's products (Bogdanov et al, 2002) or produce resistant V. destructor strains. As a result, OA is one of the chemicals most often used as a complementary miticide (Prandin et al, 2001;Gregorc and Planinc, 2001;Nanetti et al, 2003;Marcangeli et al, 2003, Marcangeli andGarcía, 2004;Marinelli et al, 2006;Rademacher and Harz, 2006;Bacandritsos et al, 2007). Nevertheless, although some studies have reported the toxic activity of OA against V. destructor, few have examined its toxic effect on honeybees (Gregorc and Planinc, 2002) because it is normally assumed that the doses used are of low toxicity (Marcangeli et al, 2003;Marcangeli and García, 2004).…”