Temperature stress can damage the sperm stored in queens, but different queen packing strategies reduce this risk.
It’s hard to imagine that by the time this issue arrives in your mailbox, it will be almost time to start making splits. Maybe past time, depending on your region. As I am writing this, it’s the middle of February and Canada is in a deep freeze — for the first time in about a century, everywhere in the country is simultaneously frozen, even Texas is cold, and Vancouver is covered in a blanket of snow. The task of making splits seems like it’s an eon away. But it’s not, and you may soon be in the market for queens to get a head start on growing your new crop of nucs. Now, where will those queens come from?
Many scientists and beekeepers advocate for purchasing locally produced queens, or, even better, rearing your own queens from survivor colonies. The idea is that local adaptation to the conditions in your geographic area will give your colonies a better chance of success in the long run. But there is another benefit to staying local: Your queens will avoid the risky business of shipping.
Canada imports around 260,000 queens every year, mainly from the U.S. and countries in the southern hemisphere, but more recently, Ukraine, Malta, and Italy are options, too. In the U.S., queens are mainly produced domestically in California, Hawaii, and southeastern states, to then be distributed throughout the nation. But while they’re being transported, those queens are at risk of extreme temperatures, which could make them duds on arrival.
In an old article in American Bee Journal titled “Shipping conditions of honey bee queens,” Dr. Diana Sammataro — a researcher formerly at the USDA bee lab in Tucson, Arizona — writes that temperatures in queen shipments within North America can fluctuate to such extremes as 19.9°F (-6.7 C) and 109 F (42.8 C). Temperatures that cold would probably outright kill the queen and are not common, but milder extremes, at both ends, are still damaging.
“Both hot and cold temperatures have been shown to negatively affect the queen’s quality,” says Andrée Rousseau, a researcher at the Deschambault Animal Sciences Research Center, explaining that “exposure to high and low temperatures reduces sperm viability inside spermatheca.” That lowers her fertility because, for example, if a queen with 5 million stored sperm experiences a viability reduction of 20%, that would mean there are 1 million fewer sperm with which to fertilize her eggs.
Last year, Rousseau and her colleagues published a study documenting temperature fluctuations in 39 queen shipments throughout the year, both within Canada and from the U.S. to Canada.1 Four of those queen shipments experienced temperatures below 59 F (15 C), and shipments sent after the middle of June experienced the most stable temperatures during their trip. Unfortunately, this means that early in the season is the riskiest time to ship queens, which is exactly when locally produced queens will not yet be available and demand for queens from warmer regions will be high. But there are other options.
“Banking queens over winter is a promising technique allowing the availability of locally bred queens to increase self-sufficiency,” says Rousseau, “and to reduce the need for queen shipping.” Rousseau and her colleagues have developed a method of indoor wintering, where queens can remain for several months with good survival and quality when they come out the other end. “We are optimistic that this technique will help the industry to face the high need of early season queens,” she says.
This technique, however, has not yet become commonplace, and it has its own challenges. Winter queen banking has had extremely variable success in British Columbia; for example, some beekeepers report 70% queen survival, while for others, all the queens died. Like eggs in a basket, it carries the inherent risk of keeping all your queens in one hive. Shipping, therefore, will still be necessary in cases when queen banks fail or spring demand outstrips the banked supply. Unfortunately, temperature stress events in shipped queens are not exactly uncommon.
Dr. Jeff Pettis, a former USDA researcher and one of my scientific advisors, documented a temperature drop (to 46.4 F, or 8 C) in one out of twelve shipments.2 In my own research, I found that one out of eight shipments experienced a temperature drop (to 39 F, or 4 C).3 On average, including Rousseau’s work, we should expect to see temperature drops in about 10% of shipments — not a negligible number — and temperatures that are too hot appear to be less common. But how cold or hot does a queen have to get before too much damage is incurred?
Pettis investigated this by conducting a huge experiment with almost 200 queens, in which he exposed them to temperatures ranging from 41 F (5 C) to 107.6 F (42 C) for different lengths of time.3 The results, which we published collaboratively in Nature Sustainability last year, show that one hour of temperature stress, whether it’s hot or cold, doesn’t cause much damage to the sperm: The average sperm viability of queens exposed to different temperatures remained more or less the same. For durations of two hours or more, however, there was a clear maximum sperm viability around 86 F (30 C), and at temperatures substantially hotter or colder than that, the sperm start to die off (Figure 1).
But it’s still not obvious how many dead sperm are too many. To estimate how many sperm need to die before it’s time to worry, I compared the sperm viability of 105 queens — half of which were rated as “failed” (spotty brood pattern, drone laying, population dwindling, etc.) by beekeepers, and half were “healthy.” But most of the failed queens were older than the healthy ones, so the following year, I repeated this survey and made sure the queens in the two groups had equivalent ages. In total, I analyzed over 150 queens, and in Year 1 and Year 2, the failed queens had an 11.5% and 12.3% reduction, respectively, in sperm viability compared to the healthy queens. The drop in sperm viability associated with queen failure is therefore reproducible, and 11.5% is a conservative estimate.
Now that we know that an 11.5% loss of sperm viability is worth worrying about, we can figure out the temperature beyond which a queen will, on average, experience an 11.5% loss of sperm viability. The answer, using Pettis’s temperature stress data, is a low of 59 F (15.2 C) and a high of ~100 F (38.2 C; Figure 1). This is only an estimate, since queens from different sources might have different temperature tolerances (this has not been investigated yet), and the threshold loss of sperm viability should also be a function of how many total sperm a specific queen has acquired, which I did not incorporate into the estimation.
But this is a good place to start; 59 F seems like a reasonable lower tolerance limit, given that it is below the temperature of a winter cluster, which averages 70 F (21 C), and is about when bees start to fall into a ….