By : Jay Evans, USDA Beltsville Bee Lab
Some people say spring starts with the mating of great-horned owls in late December. These people are greatly outnumbered. For most of us, February is a month of darkness and cold extremities. Still, it is the first month for wishful thinking and definitely a month for all plans and equipment to be in place for a successful takeoff of new packages and overwintered survivors alike. Your bees are stirring by then as well, and there is new research detailing just how much they are doing to be ready for Spring flowers.
In temperate regions, including much of North America, worker honey bees are rarely seen outside during Winter. They might search for the few available flowering plants, but mostly they will defecate and return home promptly. This does not mean bees are ignoring the oncoming spring and the need to renew and rebuild. In fact, colonies often start bouts of egg-laying and brood rearing in the middle of Winter. It is an interesting management and breeding problem to sort out whether mid-Winter brood rearing harms or hurts colonies, whether certain breeds are more prone to flipping the brood switch mid-Winter, and the specific cues bees use to start their engines.
Alphonse Avitabile (still mentoring in Connecticut and the coauthor of a leading beekeeping book) sacrificed colonies monthly through a Connecticut Winter for a 1978 study in the Journal of Apicultural Research entitled ‘Brood rearing in honey bee colonies from late Autumn to early Spring’ (https://doi.org/10.1080/0 0218839.1978.11099905). Avitabile described substantial Winter brood activity, with sealed brood averages in the thousands per colony from January onward. This was despite the presence of a true Winter in his apiaries (average high temperatures of 41, 36, and 38°F for December, January and February, respectively, today and perhaps even colder in the mid-1970s). Similarly, Lloyd Harris followed brood production in Canadian honey bee colonies entering Winter in Manitoba, Canada, also describing his findings in the Journal of Apicultural Research (https:// doi.org/10.3896/IBRA.1.48.2.01). Italian bees from California were subjected to average ‘high’ temperatures of 18oF by the time the study ended in December. Still, they persisted in egg laying, showing an average of ca. 1000 sealed brood cells when sampled on December 5. Soon after, they were moved to warmer conditions in a climate-controlled warehouse (43°, constantly), and brood numbers expanded and continued until spring (as described in a follow-up paper from 2010 in the same journal (https://doi. org/10.3896/IBRA.1.49.2.04).
Fabian Nurnberger and colleagues used an experimental approach to determine when and why bees restart brood rearing in late Winter. They describe their results in the open-access journal PeerJ in a 2018 article “The influence of temperature and photoperiod on the timing of brood onset in hibernating honey bee colonies” (10.7717/peerj.4801). These researchers followed honey bee colonies in Würzburg, Germany (average high temperatures of 39, 37 and 41oF in December, January and February). They used controlled rooms to manipulate both temperature and the day length perceived by bees. While there were complicated interactions between forced daylength and temperature, they showed in general that temperature was the strongest predictor of the initiation of brood rearing. Once bees committed to brood rearing, they continued to do so even when temperatures were reduced substantially, and the authors propose this as a risk to rebooting brood rearing in the face of an unpredictable climate.
Many beekeepers treat their colonies for Varroa mites midwinter, especially with oxalic acid treatments which are highly effective against exposed mites but ineffective against mites in sealed cells. If treated colonies harbor patches of sealed brood, oxalic acid treatments could miss substantial numbers of mites. This concern was addressed by Hasan Al Toufailia and Francis Ratnieks in England, as part of their continuing efforts to identify sustainable ways to control mites (highlighted in another Journal of Apicultural Research article, “Towards integrated control of varroa: 5) monitoring honey bee brood rearing in winter, and the proportion of varroa in small patches of sealed brood cells“, https://www.tandfonline.com/doi/abs/10.1080/00218839.2018.1460907).
Monitoring colonies in Sussex (high temperatures of 46, 45 and 45oF in December, January and February, respectively) they confirmed that December is the quietest month in terms of brood activity, with between nine and 52% of colonies having any brood at all across four study years. Variation across years in December brood incidence likely reflects warmth in late Fall and continued pollen availability. Substantial brood rearing began in January, where all colonies in each of four years had some sealed brood, averaging 1400 cells each across all years. From a management standpoint, oxalic acid treatments in December would have a more lasting impact on mite levels than treatments in January or any other month. The authors even suggest gouging out the small pockets of Winter brood prior to mite treatments as a way to achieve better Varroa control. They provide detailed methods and justification for broodless oxalic treatments at https://www.youtube.com/watch?v=2fMP9QjNy94.
Another adverse outcome of Winter brood-rearing is that female mites could both increase their progeny and improve their own health. While some Varroa mites no doubt survive months hitchhiking on adult bees, Varroa populations as a whole suffer severe Winter declines as female mites reach their limits and die. Winter brood provides a significant bridge for declining mite populations. Crudely, if there are 1400 sealed worker brood during January, approximately 110 bees will emerge daily, or 3410 in the whole month. Assuming 30% of these cells contain mites, with two female mites/ cell emerging on average, these Winter brood cells can be factories for >2000 new mites in January and maybe twice as many in February. These mites are younger and presumably more fecund than mites born months earlier. And their moms might benefit as well, since a bout of reproduction involves feeding on plump bee pupae, arguably a richer food resource than overwintering adult bees.
Early starts on brood rearing are likely to be positive on the whole, since a younger and larger bee population will be ready for Spring flowers. Still, there is a downside in terms of mite numbers and compromised mite treatments. Next year, start your Spring oxalic treatments in early December, before the owls mate.