Wetenschap - 2 juni 2016

The bee as bio-informer

Roelof Kleis

While out gathering food, bees also collect all sorts of other things in their coat and on their feet. These samples, taken inadvertently, can be used to trace, say, toxins or bacteria. Bee man Sjef van der Steen earned his PhD by studying this form of 'crowdsourcing'.

Photos Sjef van der Steen and Guy Ackermans. Bees enter their hive box through the Beehold Tubes (left and right), which are lined with wax. Through the middle, unlined tubes, they can leave the hive.

Changes in the environment leave their mark. Theoretically, if you can 'read' these marks, you have a measuring instrument. Biomonitoring is the discipline that uses living organisms to read these signs of the time. In recent years, bee researcher Sjef van der Steen has specialized in figuring out how ‘the bee colony can best be used in the study of plant pathogens and various forms of contamination’.

Beehold is the short and snappy title of his doctoral thesis. This play on words ('behold') refers to Van der Steen's most important invention: the Beehold Tube.

There are two ways you can use bees to sample the environment, explains Van der Steen. ‘You can remove a bee from the colony, kill it and analyze it. But that influences the colony's behaviour and the distribution of work and, thus, the sampling.’ As Van der Steen much prefers to leave the colony in peace and harm no bees, he has developed a tube that enables him to take samples without the bee having to die.

The principle is both simple and ingenious and capitalizes on the fact that bees enter and leave the hive by different routes. Only the approach route is relevant to the sampling process. Van der Steen uses polystyrene to seal off the landing board and installs a tube in its place. Measuring a few centimetres in diameter, the tube is lined with polyethylene glycol. This is not toxic and at room temperature is a little sticky. This tacky layer is the vital element. As it passes through, the bee loses some of its load. ‘So what I'm actually doing is stripping them down,’ says Van der Steen. ‘They walk along a hallway and wipe their feet. Between 1 and 10 percent of their load remains in the tube.’

Fire blight

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And it works. Sometimes. The best example is an experiment that Van der Steen did last year at a strawberry grower's farm in the village of Made in Brabant. Erwinia pyrifoliae presents severe problems for fruit growers. It is a bacterium that infects the flower and does great damage to strawberries cultivated under glass. In this type of cultivation bees are used to pollinate the crop. With these same bees and his Beehold Tube, Van der Steen demonstrated the presence of the bacterium before the first signs of the disease could be seen in the flowers. ‘That was the proof of principle that you can combine pollination and biomonitoring.’

As it happens, a few years earlier, a similar field test in Austria had 'failed'. There, Van der Steen was trying to demonstrate the presence of the notorious fire blight. Fire blight is caused by Erwinia amylovora. ‘There turned out to be no fire blight that year. That can happen too. Failed tests are also part and parcel of a PhD thesis. But I was able to demonstrate the efficacy of the sampling. I could see from the samples exactly what percentage of the bees had flown to flowers and what percentage had not.’

In an experiment in Bitterfeld, in the German federal state of Saxony-Anhalt, Van der Steen tried to use his informer bees to demonstrate soil contamination. ‘During the German Democratic Republic era, this was one of the world's most polluted regions. From 1951 to 1982 the pesticide γ-lindane was produced here. The chemical waste was buried or dumped in abandoned mine shafts. After the reunification of Germany, the area was remediated but the clean-up was far from thorough. In some places the subsurface is still heavily polluted.’ By way of the groundwater and soil erosion, some of this pollution gets into the atmosphere. And onto flowers.

Van der Steen was not able to demonstrate this contamination by using his bees. ‘It is there but the concentration on the flowers was too low or the tube's sorption capability was insufficient to reveal the lindane.’

Q fever

Beesourcing has obvious advantages, says Van der Steen. ‘Bee colonies are found all over the world. Many developing countries lack the infrastructure needed to monitor the environment. Using a bee colony gives you a quick indication of a contamination or a pathogen. In theory, bees form a global sampling network. In addition, the little tube is easy to replace. It doesn't require any training. Then the tubes can be sent to a lab for analysis. It is a lot more troublesome to send a dead bee.’

Van der Steen sees plenty of scope for his method. He is closely involved in a project run by Naturalis and Wageningen UR that is keeping an eye on the health of bee colonies in the Netherlands. ‘I organize the sampling done by the beekeepers. It would be nice to involve the Beehold Tube in that.’ But the technique has much greater potential. ‘It is a dream of mine to use bees to track human pathogens. How are they spread and how can you use bees to reveal that? Coming from the province of Brabant as I do, Q fever naturally springs to mind.’

In addition, Van der Steen also emphasizes that the method has its limits. ‘Bee colonies can give a clear signal but, by its very nature, this method is not able to provide quantitative measurements. Bees pass by 'by chance'. The standardization necessary for quantitative measurements is not yet possible. This is why the Beehold Tube is a signalling instrument, not a measuring instrument.’

Touch and go

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At the age of 64, Sjef van der Steen is no average PhD graduate. Having completed a higher vocation qualification in medical microbiology, he started work in 1975 as an analyst at De Ambrosiushoeve, the experimental bee farm in Hilvarenbeek. This eventually became part of Wageningen UR and the bee research transferred to Wageningen. ‘In 2000 I resumed my academic career by studying environmental science at the Netherlands' Open University.’ Once he had finished that, however, Van der Steen was involved in a serious traffic accident. It was touch and go for a while. ‘I only pulled through thanks to the specialists.’ It was an experience that left its mark. ‘I thought, now I have to get the most out of myself. And that turned out to mean getting a doctoral degree.’