6 October 2017

It’s getting autumn and while I’m writing this it is far from the right weather to work with bees. Last year about this time, I wrapped up the season. This year I spent the summer mostly at the desk and my field season begins now, when the cold arrives. Wonder why? Well, an essential part of my work are clinical studies. And they happen also in winter.

In the past month’s series, I tried to explain how interconnected bee health is, including all bee species in the concept. One recurring point was on how a healthy honey bee population protects also wild bees. Honey bees are social and they overwinter as a colony. And that’s why caring for honey bee health occurs also in winter.

Overwintering honey bee colonies begins in late summer

Winter is a critical point for bees, not only honey bees. The latter however, have to maintain their activity to a certain extent. Solitary bees or bumblebee queens go into a dormant stage during the cold months, while honey bees go into a winter cluster and keep themselves warm during this time. If they got enough high quality pollen in late summer, the beekeeper provided them enough sugar syrup to replace the honey he took from them, and if they’re at a protected, dry place they should do pretty well. But – there is something missing in this list. Diseases. Parasites. To survive the winter, a honey bee colony shouldn’t be heavily diseased.

A game changer in beekeeping has been the varroa mite. This parasite made beekeeping a much harder work than before: you have to treat the colonies to keep mites from damaging them too much. This needs constant observation. Treating at the right time before winter to get the colony over this bottleneck. And timely before the season to ensure that they will be strong enough during the warm period. I won’t go into varroa biology in detail, I’ve already done that. The important detail in this context is that the mite population doubles every month if they remain untreated. Therefore, a small infestation can result in a high burden after a few months.

Varroa mites playing chess. Eight mites in February become 1024 in September. Graph: A. Nanetti.

By a treatment in winter, the colonies start with only a few mites into the season. By a treatment in summer, you decrease the infestation of the bees that will form the winter colony. We saw a few weeks ago that this helps not only managed honey bees, but also their wild relatives

Varroa treatments on trial

Treatments against varroa mites have to be efficient on killing the parasites, but safe for the colony. They are drugs after all. And that’s where clinical studies come in. Before a product gets on the market, it has to be thoroughly tested. The part I do in the field is only an element, but a crucial one, in this procedure. It’s testing if at the end the treatment works under real condtions. But of course, it’s not giving the new product to beekeepers and wait if they like it. For answering the question “does it work?”, clinical studies follow a certain procedure to provide good data.

So, how do we measure that a treatment really kills the parasites? Well, that’s easy. We count how many varroa mites die. On trays at the bottom of the colonies you can easily count dead mites. First, you count for a while before the treatment. Also parasites die natural deaths, you need a baseline. When you did the treatment, you should already see something – there are much more mites on your tray!

Trays with sticky sheets at the bottom of the colony allow to control how many varroa mites die.

Efficacy and safety explained

And now you have to count. Every. single. mite. This is extremly important, to calculate the efficacy of a product, you need to know how many mites were in the colony. It’s not enough to know if the treatment is successful, though. You may see 3000 mites falling on your tray during the treatment. That’s a number and not much more if you don’t know how much are still in the colony. If there are only 100 remaining, you have an amazing efficacy of 97%. But if there are still another 3000, the treatment success was only 50%. Not enough to keep the colonies healthy and to protect wild bees. That’s why in clinical studies you do a so-called “critical treatment”, with another product. Then you count also the remaining mites. Again: every single mite. And then you can really tell something reliable on the efficacy of the product.

But there’s also the safety for the bee colonies. Like all drugs, varroa treatments can have side effects. Maybe not only the mites die, but also the bees. We assess this with traps in front of the colonies. Honey bees carry dead individuals out of the hive, it’s part of their prevention measures to stay healthy. In general, they come out and drop the dead bee outside. Birds, mice and yellowjackets like this: they get some extra food here. But we want to know how many bees die, so we use traps like this:

Traps in front of the colonies avoid that other animals eat the dead bees that workers carry out of the hive. Photo: M. Ligabue.

Further observations and putting them into context

It’s not 100% (wasps still get in there), but you get data if during the treatment more bees die than before. Finally, we control safety also by assessing the colony development. How many bees are in the colonies, how much brood? Do they have enough stores (nectar and pollen)? As treatments usually take some time: do they develop like they should in this period of the year? Do they behave well or do they become more aggressive because of the treatment? How do they react immediately after putting the treatment into the colony?

All these observations aren’t isolated. You have a lot of numbers at the end, but you also have to be able to put them into context. A colony with 10,000 bees in december is great. A colony with the same number of bees in May… ok, something’s happening here. Clinical studies are not only collecting numbers, it also needs some experience and understanding of honey bee biology. Only this combination will produce reliable data.

Experience helps also in other aspects: after many years doing this kind of work, I still continue to face new problems every single study I do. However, because of the experience, I see when there is a problem and can react accordingly to save the quality of the study. The colonies mustn’t have other diseases, but recognizing them needs practice. I’m adjusting the standard protocol for each study to make it the best for really answering how good a product is. Clinical studies always follow a standard framework, but a winter study is different from the next one in summer. You have to know what changes to make in each case. And by this, I hope, I’m helping to develop better treatments. To help honey bees, but also their wild relatives.

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