J. van der Steen
Wintering is the finishing piece of the bee year. It is some kind of Grand Final after a season of hard work with the bees. We supply our bees with sufficient food to survive winter, and to start happy and vivid next spring. Happily, feeding is simple as long as some prerequisites are met.
Why do we winter our bees with extra sugar? Simply because we took from the bees the valuable stock of winterfeed (honey) which the bees collected in summer, and therefore we need to supply the bees with a (not so valuable) replacement, sugar.
What do bees need in winter?
- Carbohydrates, as honey or sugar (sucrose) and/or inverted sugars (mixture of glucose and fructose). In the cells of the bee body glucose is used to deliver energy through glycolysis and citric acid cycle. Other sugars are first converted to glucose before they can be metabolized.
- Proteins, minerals and lipids. These originate from the bee bread (fermented pollen inside the cells of the comb). They are consumed by larvae as well as young adult bees by intake of royal jelly from the nursing bees. It is therefore important to start the wintering of colonies with well-nourished bees which have the potential to stay alive several months (up to six). Some breeding activity continues even in winter, therefore it is important that at the start of wintering some bee bread is in stock inside the hive.
- As few varroa mites as possible. Varroa mites parasitize pupae, resulting in weak adult bees emerging which will be hardly able to survive the winter period. They also parasitize the adult bees.
In this article I limit myself to the sugar part of the story.
What do we read in the books?
I started with reading in old books to learn what is written about wintering and found surprisingly little. On the other hand not that strange, because not so much can be sad about wintering, apart from that it needs to be enough and of good quality. Minderhout wrote in “Bijenteelt” (1928): start in August with active feeding, use a 2:1 sugar solution (2 parts sugar, one part water), continue feeding until 5 combs are full with sugar, and take care to be ready with it before mid-October. He also advises not to winter the colonies on summer honey. Why is not written, but I suppose these are primarily economic reasons.
In the ‘Handboek der Moderne Bijenteelt’(Schotman/Wedmore (1942) the only advice is to winter the bees with 22 kg breastplate. The “Grote Bijenboek (Big Bee Book)” of Groeneveld (1961) advices to winter the colonies with 10 kg sugar using a solution of 2:1. As an indication measure he states that a brood comb filled with sealed food on both sides contains 5 pounds (= ½ kg) of feed, and that a colony needs 4 – 5 full frames to carry it through winter. The feeding should be ready before 1sth of October. Van Gool writes in “Bijenhouden met Succes” (1971) about the same as Groeneveld but advices to feed until the colonies stop to take up any feed. Again the beekeeper needs to finish at the end of September to avoid winter mortality later on. In “Thieme’s Bijenboek (Ted Hooper, 1981) 10-15 kg sugar is the recommendation and this book gives the estimation that one dm2 comb sealed on both sides contains 1 pound feed. Finally the “Imkerencyclopedie” of Speelziek, Beetsma, Velthuis and others, (1987) recommends to feed more than 10 crystal sugar in a solution of 3 parts sugar ad 2 parts water, as well as that the brood nest may be soaked with feed in September.
Why at least 10 kg of sugar?
All together: more than 10 kg sugar, start timely and finish before 1sth of October.
Why then at least 10 kg of sugar? A bee needs during winter 792 mg of sugar. A winter colony of 10,000 bees thus needs at least 7,9 kg sugar, which equals about 10 kg of winterfeed. This is the theory. In practice a colony without brood uses, in a period of 26 weeks, 11 kg sugar. With brood the need is 22 kg sugar. So 10 kg (dry) sugar is really the minimum.
Because I also mentioned pollen above here some figures for pollen too: a nurse bee uses 65 mg pollen, and a colony needs at least in spring to get started 0,3 kg bee bread. This pollen is partly collected during wintering in autumn and partly in spring. In the USA one kg of pollen, and 25 kg of honey (=20 kg of sugar) is the standard.
Some decades now inverted sugar syrups are on the market in addition to normal sugar. This is mainly HFCS (High Fructose Corn Syrup). HFCS is a sugar solution produced from corn starch, which contains about 30 to 35% glucose and 40% fructose. Because the share of fructose is higher than that of glucose the solution does not crystallize. The high share of fructose is reflected in the name, high fructose corn syrup. Composition and concentration of the syrup look much alike those of honey. HFCS is about 15 x sweeter than sucrose and is applied a lot in the production of food and soda drinks.
The high share of fructose is not just nice, but also carries a risk, HMF. HMF (Hydroxymethylfurfural) is a metabolite of fructose in acid conditions. The reaction needs in addition to the acid conditions the presence of a metal ion. HMF can build up in honey as well as in HFCS because both prerequisites are met in both substrates. The pH of fresh honey is 3,7 and the pH of HFCS ready for sale 3,87. A pH smaller than 7 implicates that a solution is acid. Metal ions are present in honey because they occur naturally in nectar and pollen, and also the HFCS may contain metals originating from the plant source or from the production in vessels and storage in metal containers.
HMF is toxic for both men and bees. For honeybees concentrations up to 30 ppm are non-toxic, above 150 ppm they are. Ppm is part per million = mg per kg. According to EU directive 110/2001 honey is not allowed to contain more than 40 ppm HMF. When honey is stored at 20 degrees centigrade the HMF increases steadily with a rate of 1 to 2 ppm per month. So it does take some time before honey becomes really toxic to bees. The same holds for FFCS, but because of the industrial production process, sometimes somewhere something may go wrong. Some investigations showed that leaving the factory HFCS could contain levels of HMF between 3 and 30 ppm, when stored in a warm place this could reach dangerous concentrations rapidly. At 40 degrees storage the HMF concentration can rise from 30 to 70 ppm in a month.
Summarizing we can conclude
- Wintering with:
a. Crystal sugar (sucrose) is OK
b. Inverted sugar (HFCS) is OK, as long as a low HMF is guaranteed by the manufacturer/trader
- A minimum of 10 kg sugar is needed (about 15 kg sugar solution 2:1);
- Feeding should be ready before October 1;
- Whether we did feed enough or not can be checked by estimating the size of the winterfeed stores in the colony: at least 4 -5 full and sealed frames.
Wintering on low quality and purity sugar as well as brown sugar poses a risk. These sugars contain indigestible materials and this may accumulate in the end gut of the bee. As long as the bee can fly out to defecate this is no problem, but during cold periods it might force the bee to leave the truss and then die because of the cold. Wintering of colonies on honey is also OK, although it needs to be mentioned that honey may contain indigestible particle (pollen, spores) too which could give the same problems as impurities of sugar. In such cases it already helps when sugar is supplemented with crystal sugar or (good quality) inverted sugar.