German Federal Agency for Nature Conservation (BfN)


Impact of Pollen from Transgenic Bt Maize on Selected Butterfly Larvae


Risk assessment, GMO risk management

Research Code

201 67 430/05

Project Lifecycle

1 June 2001 – 31 December 2003 (published 2005)

Research Focus and Aims

In 2004, the global crop of Bt maize produced using a transgenic toxin from the Bacillus thuringiensis soil bacteria and able to protect itself from being eaten by insects covered an area measuring about 16 million hectares. Among other things, the study investigated the environmental impacts of Bt maize as the Bt toxin also occurs in pollen and is then carried into habitats on field fringes. Funded by the Federal Environment Ministry, the research project involved laboratory and field trials to obtain a detailed insight into the impact on and the threat to butterfly larvae from Bt maize. It was the first research work to study Germany's domestic butterfly species in areas other than farmland as these could be representative of other threatened species. The following issues were studied in detail:


Sensitivity of Domestic Butterfly Larvae

Although some varieties of Bt maize have been approved for cultivation in the EU, there has been no data available to allow detailed study of the sensitivity of domestic butterfly larvae. The project findings close this knowledge gap to an extent, showing that Bt maize pollen can have an adverse effect on the larvae of domestic butterflies like the small tortoiseshell (Aglais urticae) and the peacock butterfly (Inachis io). The findings also confirm that different species respond to the Bt toxin in very different ways. Young larvae are especially at risk from Bt maize pollen.

The toxin present in the pollen of Bt maize does not kill the larvae in every case. Rather, it can cause sublethal effects such as slower development and smaller pupae with reduced biological fitness. These effects have already been documented in a one-off study conducted on five pollen corns. Thus, the amount of pollen that can harm a butterfly larva in this way is far below that which causes premature death in caterpillars.

Rare Species Threatened Beyond Crop-growing Areas

The effects of Bt maize pollen are not restricted to cropland. It must be remembered that the amount of pollen carried on the wind drops rapidly the further the distance from the maize field and that in open conditions, sublethal effects are far more likely to occur as direct toxic effects from Bt pollen. The amount of pollen measured 32 metres from the maize field was six times higher that that known to have adverse effects on butterfly larvae. Pollen introduced into fringe habitats across this and even greater distances can cause butterflies to develop at slower rates and have lower body weights. Also, butterfly larvae whose organisms are stressed by minute quantities of Bt maize pollen are far more vulnerable to predators and disease. The cultivation of Bt maize can thus impact on the population dynamics of butterfly populations (especially those of rare species) and must be studied in more detail. The occurrence of large numbers of butterflies near maize fields was confirmed by parallel mapping of butterfly species in the Unterfranken region of Germany. The findings of the mapping activity showed that phenology and habitat preference led to the likelihood of high exposure of larvae from 26 diurnal and 53 nocturnal butterfly species.

The BBA researchers thus recommend that only those maize strains with low toxin levels in their pollen be approved, that Bt maize fields be overseeded and minimum distances to nature protection areas be prescribed.

Research Body

Biologische Bundesanstalt Darmstadt
Project Management: Dr. Gustav-Adolf Langenbruch
Project Implementation: Dr. Martin Felke

Point of Contact at BfN

Dr. M. Otto FG II 2.3

Final Report/Publication

BfN-Skripten 157 (in German)

Last Change: 05/07/2006