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Subject: Orange County, NC Beekeepers

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  • From: Randall Austin <ra41717 AT gmail.com>
  • To: Orange County Beekeepers <ocba AT lists.ibiblio.org>
  • Subject: [ocba] Confusion between climate and temperature
  • Date: Sat, 08 Feb 2014 11:25:58 -0500

Beekeepers read statements in beginner books that say something like, "you need around 60 pounds of honey to overwinter bees in temperate climates, and around 90 pounds in cold climates." They naturally assume that this is a function of temperature, since we all hate cold temperatures, right? But temperature isn't the critical issue, unless maybe you are talking about the kinds of places where you have to keep block warmers in your cars overnight to keep the engine from cracking. The issue is "climate", which is a different thing.

If I remember my Southern Living Gardening Guide correctly, spring advances at about 100 miles per week from south to north, and winter advances at the same pace from north to south. So ignoring elevation differences and other complicating factors, Washington DC has about 2 weeks shorter fall and two weeks shorter spring than Hillsborough does. That's 4 more weeks of winter, 4 more weeks of lack of being able to forage, 4 more weeks of needing food, regardless of the efficiency of the bees' metabolism.

With respect to temperature, Randy Oliver explains quite nicely how bee biology is tuned to conserving resources the colder it gets, and in fact how cold can be biologically beneficial to insects (http://scientificbeekeeping.com/old-bees-cold-bees-no-bees-part-1/) (see a quote at the bottom of this post). Cold temperatures aren't, in themselves, bad for organisms that have evolved with them; for example, certain plums require a hard freeze to produce the next year.

Remember that the important temperature isn't the temperature inside the hive (bees both regulate and adjust to that, if they are healthy and well fed). It is the temperature outside the hive, because it must be in the 50s before bees can safely fly to defecate and to forage. If someone figures out how to control THAT (short of moving the hives), please post the solution as a "reply to all".

In our climate, it is moisture that is the winter enemy, not temperature. If we make our hives nice and snug, we trap in moisture, which kills bees. Go ahead and try if you want; I am only relating how I keep my bees alive (and have been doing so successfully for years), not how anyone else should keep theirs alive (if that's their goal).

Randall Austin

Cited quote:

The colony still has more tricks up its collective sleeve! By clustering over any remaining brood, and allowing the outer shell of the cluster to drop to 41ºF, the bees can conserve their energy and food stores until needed for broodrearing after the winter solstice. The cluster core has an incredible ability to generate heat—it can produce a metabolic rate equal to that of a shrew (Kronenberg & Heller 1982)! However, the bees make every effort instead to conserve energy, and trap the metabolic heat from the core by tightly packing their bodies into an efficient insulation.

Even more remarkable, van Nerum & Buelens (1997) describe how the colony conserves energy and water by reducing ventilation with the tight winter cluster. The bees allow carbon dioxide levels to rise to as high as 6% (5% is dangerous to humans) inside the cluster. At the same time they create a condition of hypoxia (low oxygen), reducing the oxygen level from the 21% in the atmosphere to about 15%, which induces them to enter into an “ultra low metabolic rate”—similar to the diapause that other insects use to survive the winter. In this state, the colony uses minimum energy, and traps critical metabolic water within the cluster (the center experiences low relative humidity, and the cooler shell traps escaping moisture). (No mention was made of the effect that such an extraordinarily high CO2 level would have in increasing the acidity of the haemolymph—this may be an effect deserving a bit of research).

The authors may have overlooked yet another benefit to hypoxia—to avoid oxidative aging (Fridovich 1977). The bee respiratory system is extremely effective at diffusing oxygen into the tissues—some 200,000 times faster than our human delivery system that uses blood (Burmester 2005). He states that “oxygen is a double-edged sword: although required to fuel energy production, it is also a potent source of toxic compounds known as reactive oxygen species (ROS), which can damage proteins, DNA and lipids. In recent years, ROS have been recognized as a major threat to cell survival, and toxic ROS effects are suggested to underlie ageing and cell death. Therefore, it is advantageous to keep cellular oxygen levels just high enough for efficient mitochondrial respiration, and as low as possible to minimize oxidative damage.”





  • [ocba] Confusion between climate and temperature, Randall Austin, 02/08/2014

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