American Bee Journal • October 2019 Vol. 159 No. 10 • Notes from the Lab: Crowded Apiaries

Whether we acknowledge it or not, all beekeepers are farmers who are responsible for keeping domestic animals (our bees) healthy and productive. If you have a couple colonies in your backyard, you may simply enjoy watching your bees and stealing a couple gallons of honey every now and then. If you’re a commercial beekeeper, you’re making your living from keeping your bees healthy and productive.

Of course, one risk of keeping lots of domestic animals close together is the potential for outbreaks of disease. Just think of the large-scale poultry farms and livestock facilities that invest great effort into minimizing disease. Or, if that example doesn’t work for you, think of the kindergarten classrooms where new parents basically expect their children will get sick when they send them off to school.

So, does the same thing apply to our bees? Should we worry about the density or positioning of colonies in an apiary if we want to maximize “herd health”? This is the topic for our twenty-third “Notes from the Lab,” where we highlight “Industrial bees: The impact of apicultural intensification on local disease prevalence,” written by Lewis Bartlett, Carly Rozins and colleagues and published in the Journal of Applied Ecology [00:1-11 (2019)].

Bartlett, Rozins and colleagues’ study was motivated by two main observations. First, it’s now common knowledge that honey bee colony losses are unsustainably high, and one of the main reasons for high loss rates is disease. Indeed, there’s good evidence that viruses transmitted by varroa, particularly Deformed Wing Virus (DWV), may be the main world-wide driver of honey bee colony losses. Second, we know very little about how diseases are spread between honey bee colonies, and we know even less about how different apicultural practices impact disease risk. That’s a pretty important gap in knowledge given observation #1.

Changing the number or arrangement of colonies in an apiary can potentially influence disease by altering the size of the bee population, frequency of “drifting” between colonies, and network of connections between colonies. To start addressing this question of how different numbers or arrangements of colonies impact risk from disease, the authors created new analytical and agent-based epidemiological models to understand how different factors shape transmission, spread and prevalence. In other words, they used data to predict how the number and arrangement of colonies in an apiary impact disease.

Now, there are probably very few epidemiologists out there who are reading this column. But everyone can understand a major chunk of epidemiology by knowing only one thing: the basic reproduction number of a disease, R0. If R0 is less than 1, prevalence in a population decreases and the disease eventually dies out. This is obviously what epidemiologists love to see, since no one loves disease (aside from a few researchers who study it, but even those researchers were muttering some pretty nasty things about disease during a norovirus outbreak at the recent Ecology and Evolution of Infectious Disease conference in June, where ~40% of attendees became infected! Yes, the irony of a disease outbreak at the Ecology and Evolution of Infectious Disease conference was not lost on its attendees, including some of the authors of this study and the author of this column). Anyways, back to R0. If R0 is greater than 1, the disease spreads and prevalence in a population increases. Such was the case for the norovirus that spread rapidly from one host to infect 40% of the conference attendees.

So, what did they find? Did the arrangement of colonies in an apiary impact R0? Yes. The authors considered three types of arrangements (Fig. 1), and R0 was always greatest for the lattice configuration. This is primarily because the lattice is the most highly connected configuration, where bees “drift” between colonies in many different directions (Fig. 2). Conversely, “drift” is reduced in the circle and array configurations, and therefore disease is transmitted less. So, if you want to minimize disease transmission in your apiaries, arranging your colonies in an array or circle is likely to help.

What about the number of colonies in an apiary? Did that impact R0? Yes. As predicted, the more colonies you have in an apiary, the greater R0. Interestingly, this varied in magnitude according to configuration. R0 continued to increase throughout all sizes of the lattice apiaries, while it largely leveled off in the array configuration and remained constant throughout all sizes of a circle configuration. This is because the average number of neighbors is reached quickly in the array and circle configurations, while it continues to increase slightly in the lattice configuration. So, if you’re looking to minimize disease transmission in your apiaries, crowding them less, especially if they’re arranged in a lattice, will help.

So, this means I should keep my apiaries small and arrange my colonies in an array or circle, right? Given what you’ve read above, that’s probably your take-home, right? Well, unfortunately it’s not that easy. The authors found that decreasing R0 only caused meaningful decreases in disease prevalence (i.e., the bottom line for the health of your bees in your apiary) when R0 was initially low. Indeed, only diseases with a base R0 around 3 were likely to be impacted in a meaningful way by the number or arrangement of colonies in an apiary. Furthermore, when they looked in the literature, most of the major honey bee diseases that we worry about (Nosema, American Foulbrood, Deformed Wing Virus, the acute paralysis virus complex) appear to have base R0 values much higher than 3. For example, Nosema ceranae is estimated to have a base R0 around 23, and other honey bee diseases appear to be similar. So, while you can certainly take steps to reduce disease transmission in your apiaries, the important diseases for honey bees are so contagious that there’s probably not much you can do to reduce prevalence by altering apiary arrangement or size.

Eek, that doesn’t sound good. So, what can I do? For one, investing in disease-resistant stock will help. You know those friends of yours who never seem to get sick? Part of the reason is likely that they have good genes for resisting disease. Similarly, there are a wide variety of diseaseresistant honey bee stocks available and lots of interest from beekeepers, yet our data show that few beekeepers are taking the plunge and actually purchasing those stocks. Maybe now is the time.

In addition, just like us, bees need good nutrition to resist disease. And while the authors didn’t incorporate nutrition into their models, that’s probably the first thing most of us consider when stocking an apiary. How many colonies can be supported by the forage at a particular location? While this decision is still largely driven by beekeeper experience, efforts are underway to understand how landscape-scale resources from lots of surveys and satellite data (think Google Maps, but a lot better) can predict honey bee health and disease resistance. For example, check out the new tool called “Beescape”: https://beescape.org/.

Finally, given that last month’s Notes from the Lab was about controlling varroa, I’m not going to belabor the point. But please monitor for varroa in your colonies and control it when it’s time .

We have several tools at our disposal to minimize disease in our bees. Bartlett, Rozins and colleagues have showed that other techniques are worth more of your time than worrying about apiary configuration and density. I don’t know about you, but I always appreciate one less thing to worry about.

*Bartlett, L. J., *C. Rozins, B. J. Brosi, K. S. Delaplane, J. C. de Roode, A. White, L. Wilfert and M. Boots. 2019. Industrial bees: The impact of apicultural intensification on local disease prevalence. 2019. Journal of Applied Ecology 00:1-111. https://doi.org/10.1111/1365-2664.13461

Scott McArt, an Assistant Professor of Pollinator Health, helps run the Dyce Lab for Honey Bee Studies at Cornell University in Ithaca, New York. He is particularly interested in scientific research that can inform management decisions by beekeepers, growers and the public.