Effects of Bt maize on honeybees

(2008 - 2011) University of Bayreuth, Department of Animal Ecology I, Population Ecology Working Group

Topic

The aim of the project is to investigate the potential effects of the genetically modified Bt maize cultivar MON89034xMON88017 on honeybees. This maize produces three Bt proteins , making it resistant to both the European corn borer and the Western corn rootworm .

The project will examine the following questions:

Does ingestion of Bt maize pollen have undesirable effects on the development of bee colonies or on individual honeybee larvae? Is the bees’ ability to survive the winter affected?
Does ingestion of Bt proteins reduce the bees’ resistance to other stress factors, e.g. pathogens?
Does the presence of Bt maize pollen have direct toxic impacts on bee parasites and therefore potentially indirect positive effects on bee colonies?
How much maize pollen is actually carried into beehives as a function of the structure of the surrounding agricultural landscape?

Experiment dedcription

In order to differentiate between maize varietal effects and Bt effects, two other conventional maize varieties will be planted as a control in addition to the genetically modified variety and the isogenic parent variety. In addition, the isogenic variety will be treated with a soil insecticide.

Honeybee hives are placed in flight tents measuring 4x12 metres in area and 3 metres high during the maize-flowing period.

Dead traps are installed In front of the man-made bee hives that house the bee colonies, through which the number of dead bees can be recorded.

The hives are opened to document the development of the colony.

The bee with the green markings is the queen.

Effects of Bt proteins on honeybees

Two beehives with approx. 1000 workers are placed in a flight cage on each of 32 selected plots on the trial field at the start of the maize-flowering period.

A trap is used to count the number of dead bees each day. Changes to the size of the colony are documented throughout the trial period using a special method (Liebefelder estimation method). The fitness of the bees that were raised on Bt pollen as larvae is quantified by measuring the emergence weight.

At the end of the trial, the colonies from the field trial are encouraged to enter the overwintering phase under controlled feeding and temperature conditions. Their development is monitored.

At the same time, laboratory experiments are carried out with individual bees:

Newly emerged worker bees are taken from the trial colonies raised in the flight tents and moved to the laboratory to assess their individual lifespans.
Bees are fed with different concentrations and combinations of pure Bt proteins to test whether the three Bt proteins produced by the maize variety under investigation have undesirable effects on honeybees when combined.
For in vitro breeding of larvae, the young bee larvae are raised under standardised laboratory conditions with synthetic feed to which pollen from the different test maize varieties or even pure Bt-protein can be selectively mixed. In this experimental approach, it is possible to exactly measure how much feed and BT-protein the larvae consume. After these arteficially raised bees emerge they can be further examined, e.g. through feeding with pollen from the different varieties of test maize.

Combined effects of Bt proteins and pathogens on honeybees

In the second and third trial years, half of the colonies on the trial plots with the Bt and isogenic maize varieties will be infected with a bee disease - Varroa mites in the second year and the unicellular gut parasite Nosema in the third year. The development of the bee colonies will be assessed in the same way as described above.

In order to be able to conduct experiments over a longer period of time and outside the maize-flowering period, further trial colonies will be placed on other trial fields. Some of them will be infected with the pathogens mentioned and fed with pollen from the genetically modified and isogenic maize varieties grown in the greenhouse. These colonies can be used to investigate e.g. what happens if they are fed different proportions of other pollen types in addition to maize pollen.

Effects of Bt proteins on parasites in the bee colony

The greater and lesser wax moth and the small hive beetle are to be investigated to see whether they are sensitive to possible residues of Bt proteins. Pieces of honeycomb containing hatched larvae will be taken from the beehives on the trial plots with Bt maize and the isogenic variety and fed to the bee parasites. The development of the parasites will be monitored.

In addition, bees and bee products from the trial colonies reared on Bt maize will be examined in the laboratory for residues of the Bt proteins.

Potential exposure risk of honeybees in relation to Bt maize

Fifteen landscape areas will be selected that differ from one another in terms of the proportion of land area under maize cultivation and the availability of alternative pollen sources during the maize-flowering period. At the beginning of July, standardised young colonies with pollen traps will be set up in these areas. With the pollen traps it will be possible to measure the pollen spectrum used by the bees each week. In this way, it should be possible to draw conclusions about how much maize pollen is actually carried into beehives as a function of the structure of the surrounding agricultural landscape, and the potential exposure risk of bees in relation to Bt maize.