Research Reviews
What are the top management concerns for U.S. beekeepers?
Answer: Many and varied, depending on the number of hives you manage
Nationwide, this has been a pretty brutal winter. In North Carolina, we've had more snow than most years. Honey bee colonies are pretty well able to take such weather in stride. It is said that honey bee colonies don't freeze to death, they starve to death. This is because when it gets cold outside, the bees cluster to minimize heat loss. When it gets really cold (say, below 10ºF), they even start to "shiver" to generate heat within the cluster. The long-lived winter bees (which are physiologically different from their summer counterparts, enabling them to live for months rather than weeks) thus consume the honey that they've stored away as their energy source to keep warm all winter long, so as long as they have sufficient honey, they should be just fine.
Nonetheless, winter is the time when most beekeepers experience most of their losses because it is still quite a stressful time for a colony (unpredictable temperature swings, delayed onset of spring, etc…). Thus understanding the reasons behind winter losses are important to helping minimize them; some things are unavoidable, but our job as beekeepers is to do our best at avoiding the avoidable.
There have been a slew of winter-loss surveys in recent years, all of which have been very insightful at teasing apart the different factors that lead to colony demise. This most recent survey, again published by Dennis vanEnglesdorp and his colleagues, present data from last winter (2009-2010) since, after all, it takes quite a bit of time to solicit the information, analyze it, write it up, and get it through the entire peer review process (hence why the process of science is painstaking slow, so a one-year turnaround is really fast!). The report has some similarities with previous years, but also some notable differences.
First, some of the basic statistics. The overall colony losses were 34.4%, right around where previous years have been (plus or minus 5-10%). The average loss for each beekeeper was 42.2%, which is higher because many of the larger beekeepers (more than 500 hives) lost a disproportionately lower number of their colonies (many beekeepers assume the opposite, that large-scale beekeepers have higher losses because they are more abusive to their colonies, but this seems not to be the case). Given that they "acceptable" level of losses of the surveyed beekeepers was 14.5%, these numbers are still disturbing no matter how you look at them.
Now to look inside these numbers. Since the majority of the 2.4 million beehives in the U.S. are trucked to northern California in order to pollinate the almond crop, there is a significant management concern about what riskss, if any, the exposure to those orchards might pose. The survey suggests that beekeepers that had bees in almonds, compared to those that did not, had lower losses on average. The same was true for those who moved their colonies at least once the previous year compared to those who kept their bees in place. Thus the migratory nature of bees does not seem to significantly increase the relative risk of their mortality, at least at the superficial level.
More importantly, the self-identified "culprit" of colony death by each surveyed beekeeper varied depending on the scale of their operation. Smaller-scale beekeepers tended to identify "manageable" factors, such as starvation or insufficient colony populations going into winter, as the top reasons for colony mortality. These factors seem to be something that we can have some control over. Larger-scale beekeepers, on the other hand, tended to identify relatively unpredictable factors, such as "poor queens" (27% loss), mite loads (40% loss), and pesticides (45% loss) as their top issues.
So it appears that different management practices can greatly influence the welfare of bee colonies, for both better and for worse. Given that most beekeepers are smaller-scale, and that most small-scale beekeepers reported starvation (44% loss) and weather (57% loss) as the top two factors for colony mortality, then we can go a long way at bolstering the health of our collective honey bee population by ensuring that our hives have sufficient honey stores to make it through a longer-than-average winter.
Reference
vanEngelsdorp, D., J. Hayes, R. M. Underwood, D. Caron, and J. Pettis. (2011). A survey of managed honey bee colony losses in the USA, fall 2009 to winter 2010. Journal of Apicultural Research, 50: 1-10.
