Sep 21, 2011
No risk to butterflies from genetically modified Bt maize
“The pollen quantities that led to higher mortality rates in caterpillars in the laboratory were not detected in the field.”
Can butterflies be harmed by genetically modified Bt maize? This was the question that Mechthild Schuppener from RWTH Aachen University investigated in a three-year research project. She conducted a feeding study in the laboratory to find out how sensitive caterpillars are to Bt maize pollen. In the field, the scientist investigated how much maize pollen lands on butterflies’ food plants under natural conditions and examined where butterfly nests are to be found in farming areas. GMO Safety spoke to Mechthild Schuppener about the findings of her research project.
Mechthild Schuppener from the agricultural ecology research group at RWTH Aachen University (Institute of Plant Physiology, Bio3), conducted a three-year research project to investigate whether butterflies could be at risk from the cultivation of genetically modified Bt maize.
She studied the small tortoiseshell and peacock butterfly (in photo above). Mechthild Schuppener bred the caterpillars for her feeding experiments herself.
In the laboratory she fed caterpillars with various concentrations of pollen from Bt maize.
In the field she investigated how much pollen landed on pollen traps and on stinging nettles at various distances from the maize field.
GMO Safety: You wanted to find out whether the cultivation of Bt maize could harm butterflies. Which butterfly species did you study and why?
Mechthild Schuppener: We chose two species of butterfly: the small tortoiseshell and the peacock butterfly, because these two species are common in agricultural landscapes and because their caterpillars develop during the maize-flowering period. Also, the two species are monophagous, in other words the caterpillars feed on only one type of plant, the stinging nettle, which is also common in agricultural landscapes. This makes it easier to record the presence of caterpillars properly.
GMO Safety: The Bt maize you studied was a type that produces three different Bt proteins. What did this mean for your research?
Mechthild Schuppener: Two of the three Bt proteins are effective against the European corn borerr, which is a moth. That was why we wanted to see whether other butterflies and moths could be affected or potentially harmed by these Bt proteins. Also, there has been very little research so far into maize varieties that produce more than one Bt protein. We deliberately chose this maize to find out whether there are any combined effects. For instance, the effects might be greater; the two proteins could have a cumulative effect.
GMO Safety: What approach did you take?
Mechthild Schuppener: First of all, we conducted experiments in the laboratory to answer questions concerning the toxicity of the Bt proteins. We wanted to find out what happens if the caterpillars eat pollen from Bt maize. To do this, we applied pollen suspensions to pieces of stinging nettle leaves in different concentrations and gave them to the caterpillars. We investigated a number of different aspects: feeding activity, weight gain, the time taken for the caterpillars to develop and the mortality rate. Then we investigated in the field whether the caterpillars do actually come into contact with maize pollen in their natural environment. We investigated how far maize pollen spreads by setting up pollen traps and stinging nettle plants at various distances from the edge of the field. We also carried out studies at landscape level to see where caterpillars are found. Are they found near maize fields or do they develop far away from maize fields?
GMO Safety: Did you detect any sensitivity in the caterpillars to Bt maize pollen in the laboratory and if so, at what pollen concentrations?
Mechthild Schuppener: Yes, we did detect effects. We were expecting to because the pollen contains Bt proteins that are effective against moths and butterflies. The first effects became visible in the range of 200 to 300 pollen grains per cm². The caterpillars fed on Bt maize pollen ate less. The higher the pollen dose, the greater the effects. We were able to show that very clearly. At 1000 pollen grains, the mortality of the caterpillars given Bt maize pollen was much higher than for the control group, which was fed on pollen from conventional maize.
GMO Safety: Was the effect the same for both species of butterfly?
Mechthild Schuppener: We were able to repeat the experiments lots of times on the small tortoiseshell. Unfortunately, we were not able to do the same with the peacock butterfly because we did not have enough caterpillars. Based on what we were able to test, however, it looks as if there is not much difference between the species in terms of their sensitivity. However, one would have to carry out further tests on the peacock butterfly.
GMO Safety: In the field you investigated to what extent the caterpillars come into contact with maize pollen under natural conditions. Did you find concentration levels that would suggest they were at risk?
Mechthild Schuppener: We found the highest pollen quantities on the pollen traps and stinging nettle leaves right next to the field. At a distance of five metres from the edge of the field the pollen quantities were already much lower. Pollen quantities fell rapidly with increasing distance from the field. Right next to the edge of the field we found an average of 150 pollen grains per cm² in the pollen traps. The stinging nettle leaves contained only a fifth of this quantity. We were able to find the odd stinging nettle leaf with up to 200 pollen grains per cm², but those were isolated cases.
GMO Safety: Why is it that so much less pollen stays on the stinging nettle leaves?
Mechthild Schuppener: The pollen traps have a sticky surface that the pollen grains stick to, whereas stinging nettle leaves are not sticky, so the pollen can roll off, be blown off by the wind or washed off by rain.
GMO Safety: Would it be possible in individual cases for caterpillars to eat lethal quantities of Bt maize pollen?
Mechthild Schuppener: The pollen quantities that led to higher mortality rates in caterpillars in the laboratory were not detected in the field. It is possible that such pollen quantities can be found inside maize fields, but you do not find caterpillars of the tortoiseshell or peacock butterflies inside maize fields. In general, we can assume that the two butterfly species can cope with some losses. After all, there are many other dangers that can kill caterpillars, including parasitoids, predators, disease and bad weather. Neither are caterpillars likely to survive the occasional mowing of field margins. But such losses can be compensated for.
GMO Safety: Is the distance of the food plants from the maize field the key factor that determines whether caterpillars come into contact with Bt pollen, or are there other factors?
Mechthild Schuppener: Another condition is that the caterpillars have to be there during the maize-flowering period. In Germany, both butterfly species usually have several generations in one year. The first one develops in the spring and the second in the summer. The development periods vary though, so a high proportion of the caterpillars develop before or after the maize-flowering period and only some of them are around during the maize-flowering period itself. And not all of these will develop in the immediate vicinity of maize fields.
GMO Safety: What did you discover when you mapped agricultural landscapes?
Mechthild Schuppener: We investigated two different agricultural landscapes: a region that grows a lot of maize and a region that does not grow much maize, and looked to see whether any caterpillars of the small tortoiseshell and peacock butterflies are found in these regions during the maize-flowering period. In both regions we were able to demonstrate that some caterpillars do develop in the vicinity of maize fields, but that some develop a long way away from maize fields. This means that individual caterpillars are exposed to maize pollen, while others have no contact with maize pollen at all.
GMO Safety: In summary, what is the result of your research?
Mechthild Schuppener: In the laboratory we were able to detect effects, which was to be expected, since the pollen contains Bt proteins that target moths and butterflies. In the field we were able to detect only small quantities of maize pollen on the butterflies’ food plant, the stinging nettle. We were also able to show that only some of the caterpillars are to be found near maize fields. Overall, one can say that the risk to the butterflies from this type of Bt maize is negligible.
GMO Safety: Thank you for talking to us.