Recommendations for Over-wintering Honey Bee Colonies on Cape Cod
John Portnoy, Wellfleet, 11 Oct 2021
With the arrival of Varroa mites and mite-vectored viruses, overwintering honey bees successfully, and having strong colonies ready for the earliest spring nectar flows, have become much more difficult. Unfortunately, advice in popular beekeeping books and websites can be conflicting, outdated and with little control on its quality. Much of it is repeated dogma, i.e., not well founded on scientific studies, and not necessarily applicable to coastal New England conditions. This can result in confusion among many novice beekeepers, failure to perform critical management actions, and frustration when colonies die during winter. Clearly, Cape beekeepers in general would benefit from guidance that distills the most up-to-date science on sustaining our bees through the winter.
Having kept bees in Wellfleet for a long time, followed the peer-reviewed literature, and experienced increasing success in carrying strong colonies through winter, I offer these rough guidelines. This is a “work in progress”, which I expect to modify with more local experience along with research findings from elsewhere. I recognize three principal factors for over- wintering success: genetics, nutrition and mite control.
All honey bees (Apis mellifera) in North America derive from stock imported from Europe since the 1600s; however, European honey bees comprise many distinct subspecies, each evolving separately in geographic isolation over thousands of years to survive in the wide range of European climates. With this history, it should not be surprising that honey bees from sub- tropical portions of Italy, for example, would fare poorly through a New England winter. In fact, a large pan-European study found that local bees consistently performed better than bees transplanted from even a few hundred miles away (https://doi.org/10.3896/IBRA.1.53.2.03). Thus, it is best to use locally selected honey bee stock with demonstrated adaptations for survival through a Cape Cod winter. Several BCBA beekeepers have been attempting to select for these traits by breeding from winter survivors that are otherwise gentle and productive, and usually have locally selected queens or queen cells available from late May through July.
Recommendations for minimal honey stores, usually expressed as gross hive weight, for winter survival in New England are unfortunately all over the map. However, 20 years of scale-hive data from Wellfleet indicate that a colony in a double-deep or triple-medium hive (including woodenware, bees, stored food and all) winters well if weighing at least 120 pounds gross hive weight in late September, and no less than 100 pounds at the end of brood rearing in November. On average, colonies – those that have survived the winter - have lost about 34 lbs from September to April, with a range of 20-41 lbs. (see graph below) For insurance, more stores are better. Lighter colonies need to be fed with 2:1 sugar:water syrup preferably from late August through early October. If they are still underweight in November, the only options are honey comb taken from other hives or dry sugar feeding on top bars for the rest of winter. Colonies that weigh at least 100 pounds at the beginning of winter have enough carbohydrate without additional feeding until brood rearing accelerates in March. It is then good insurance to provide dry sugar overhead through mid-April, mainly because we often get extended periods of cold and rain when the bees cannot forage.
Lacking the means to weigh entire hives, one should leave or provide a colony at least the equivalent of a medium super plus several frames in the brood chamber filled with capped honey and/or syrup, i.e., about 60 pounds of carbohydrate stores. In any case, these stores should be concentrated on the sides and especially above the winter cluster; the bees usually arrange this on their own. Note that at least on the outer Cape, there is little nectar flow and colony weight gain after mid-August, so plan accordingly by leaving enough honey or compensating with thick (2:1, sugar:water) syrup feeding.
Besides carbohydrate, the bees obviously require protein especially for brood rearing. Some beekeepers supplement bee-collected pollen with commercially available pollen substitutes. These seem to help; however, there’s not yet wide agreement about the best time to feed supplemental protein, or whether it is even necessary given the local availability of pollen, which is not well known.
Varroa mite infestations and mite-vectored viral infections are the primary causes of winter colony loss here.
In a nutshell, to protect the winter bees from mites and especially viruses, mites must be controlled BEFORE winter bees are reared in August and September. This means monitoring beginning in early July at the latest and controlling mite infestations that exceed accepted thresholds (e.g., 3 mites per 100 bees in alcohol wash or sugar shake) in some fashion in those bees that rear the winter bees. If one delays mite control until November, the winter bees will likely already be infected with debilitating viruses; as a result, the colony will die during fall or winter, or be very weak by spring. Interestingly, a study showed that effective mite control in summer is followed by a crash in virus infections about four weeks later, simply because the virus-carrying summer bees died of old age; in contrast, mite control only in November meant that the long-lived winter bees suffered with virus infections all winter, and usually died en masse before spring. That is why it is absolutely critical to control mites in the summer bees that raise the winter bees, to minimize winter-bee virus infections. This practice is resulting in much improved winter colony survival on the Cape and elsewhere.
Besides Varroa mite control in summer, mite counts in the fall greater than 5% (e.g., 5 mites per 100 bees) call for treatment, typically using an oxalic acid dribble or vaporization. Oxalic acid is most effective on adult bees; therefore, it should be applied no earlier than November and no later than late December, a period when most colonies have little or no brood.
Effective mite monitoring methods include powdered sugar shakes and washes with alcohol, window-washing fluid, or a dish-washing soap solution; these methods yield an infestation rate, for example, mites per 100 bees. Natural mite drop onto sticky boards can give a rough idea of the mite load but can be misleading because it varies greatly from day to day and does not account for colony size.
Effective mite control methods include synthetic pesticides, organic acids, essential oils, and biotechnical practices like queen caging for brood interruption. Check with the Bee Informed Partnership, Honey Bee Health Coalition, BCBA and the MDAR Apiary Program for current recommendations.
Other factors Affecting Winter Survival:
Although some queens remain fertile and productive for years, most show peak egg-laying performance during their second summer, declining thereafter. For this reason, it is best to replace queens annually or biannually.
Winter Hive Configuration
There is much debate here but there seems to be consensus on at least top insulation. Besides retaining heat (most is lost through the top and not the sides of the hive), top insulation prevents the condensation of water vapor that would otherwise drip onto and chill the winter cluster. If water-absorbent, the insulating material should have enough ventilation, and/or be changed periodically, to avoid becoming saturated with water during the long winter. Non- absorbent closed-cell foam is a good alternative. In addition, many Cape beekeepers wrap their hives with tarpaper, house-wrap, geotextile fabric, etc. to block the wind; black materials also provide some solar gain on sunny days, which allow the bees to break cluster enough to reach winter stores. The benefits of winter wrapping are unproven, but it is easy and very likely does no harm. Beyond wrapping, some beekeepers in very cold climates use insulation on hive sidewalls to increase heat retention and reduce the need for clustering; this practice may be helpful here.
Pests and Diseases other than Varroa Mites
Most of these afflictions will be avoided simply by maintaining strong colonies throughout the year. For example, wax moths, small hive beetles and even diseases like European foul brood and chalkbrood will often be controlled by the bees themselves if colonies are populous and always well-nourished.