Frequent flyers under surveillance

"Bees are lazy", says Dr. Martina Sick from the Federal Biological Research Centre for Agriculture and Forestry (BBA). She should know. Together with a research team from the Federal Agricultural Research Centre (FAL), Martina Sick is studying the effects of transgenic oilseed rape pollen on bees. She has discovered that bees do not differentiate between pollen from genetically modified and conventional plants. They fly straight to the plants nearest their bee colony. How much transgenic pollen might the bee food contain as a result? And what impact does this have on the bacteria in the bee’s intestine?

Pollen load

To answer these questions, Martina Sick and her colleague Dr. Stefan Kühne have set up a field trial near Dahnsdorf, Berlin. Genetically modified, herbicide -tolerant rape is grown in rotation with conventional winter rye and winter wheat in rectangular plots.

The researchers have set up several honey bee and bumble bee colonies in the field margin. They have also made artificial nests for mason bees. Martina Sick and her colleagues have been taking samples of the pollen load that the bees carry on their hind legs since the first year of the project in 2001. They are also studying the pollen in the brood cells and food stores of the three bee species. Using PCR techniques the scientists determine the proportion of transgenic pollen in the total amount of pollen collected by the bees. From this they can deduce, amongst other things, the composition of the bee larvae’s food.

Adverse conditions

The researchers’ work is not easy. In 2001, the first year of the project, they first had to gather methodical experience to optimise the trial set-up in the second year. For example, significantly more mason bee cocoons were used in spring 2002 to enable the researchers to observe a sufficient number of insects. Then there was the night of 22 March 2002 when anti-GM activists destroyed the trial field. They tore out most of the oilseed rape plants. "Fortunately, enough plants survived and new ones grew again, so in the end we were still able to complete the experiment", explains Martina Sick.

It quickly became clear that the flowering time of the plants and the vicinity to the bee colony are key influencing factors. If the beehive is right beside a transgenic oilseed rape field in flower, the bees gather a large proportion of pollen there. If the rape has finished flowering, the bees seek out other pollen sources. Or vice versa: if the bees are kept away from transgenic rape, they will gather pollen mainly from other, nearer plants. The researchers need to collect and evaluate still more data to be able to make statistically reliable statements about the proportion of transgenic pollen in the bee food. This is expected to take place in 2003.

The scientists are not content with studying the pollen alone. They are also looking at whether genes from the plant pollen can be absorbed by bacteria in the intestine of the bees; in other words whether horizontal gene transfer takes place. To this end scientists at the Biological Federal Research Centre have become insect surgeons: under sterile conditions they remove the pollen-filled intestine from the bees and their larvae. They send the intestines to the research team of Dr. Christoph Tebbe and Kathrin Mohr at the Institute of Agroecology at the FAL in Braunschweig.

Pioneering work

Last year Kathrin Mohr carried out pioneering work on the bee intestines: she used a new molecular technique to analyse which bacteria occur naturally in the intestines of the three bee species under examination. The graduate biologist was able to identify more than 90 different species of bacteria. She also came across herbicide-tolerant bacteria. This came as no surprise to the experts at the FAL. Between 10 and 50 percent of naturally occurring bacteria exhibit certain tolerance traits. But nonetheless, Christoph Tebbe wants to know specifically whether the herbicide tolerance of the intestinal bacteria is of natural origin or has resulted from the horizontal transfer of genes from the pollen to the bacterium. "On the basis of current scientific knowledge, bacteria do not normally absorb foreign DNA from higher organisms in natural conditions, so not from plants either", explains the microbiologist. "But we would like to get to the bottom of this. In the months to come we will create conditions in the laboratory which maximise the potential for gene transfer. We will in fact provoke horizontal gene transfer."