Jonathan Latham and Allison Wilson
Pollen from a Bt insect resistant maize is highly toxic to the European common swallowtail butterfly (Papilio Machaon) according to a paper published last week in the journal Basic and Applied Ecology (Lang and Vojtech 2006 Vol. 7 pp296-306; doi:10.1016/j.baae.2005.10.003). The paper found that for first instar caterpillars the LD50 of Bt 176 corn was 14 pollen grains and that for harm to occur required consumption of as few as 5 pollen grains.
In much of Europe, maize sheds large quantities of pollen in July, which coincides with the feeding of second generation swallowtail caterpillars. The results therefore have potentially great ecological significance for these butterflies since their host plants occur on field margins where maize pollen is abundant. The implications of this work extend beyond swallowtail butterflies. Other butterflies and moths (Lepidoptera) may also be susceptible. Previous studies have suggested that the two European butterflies (and the one moth) studied so far vary in their sensitivity to the transgenic Cry1ab protein in Bt 176. All were affected but P. machaon would appear to be the most sensitive species so far tested. Although the chief effect of pollen toxicity is likely to be on caterpillars feeding on field margins, maize pollen can travel at least several kilometres and therefore may pose a hazard at a considerable distance or to neighbouring wildlife reserves. According to Matt Shardlow Director of the UK-based invertebrate conservation charity Buglife, such hazards “may well push it (the swallowtails) towards extinction, along with the endangered wasps that feed on them”. Bt 176 corn has been approved for cultivation in Europe and is grown mainly in Spain.
The European approval process for transgenic crops has been criticised consistently and heavily in recent years, in particular for failing to draw sufficiently on ecological expertise. This result suggests that the spectre of widespread ecological damage arising from transgenic crops can no longer be considered unfounded speculation. Matt Shardlow believes that “all GM crops should be rigorously tested for their impact on invertebrates which are the foundation of life on earth. If they are failing to do that then they are not adequate.”
Lang, A. and Vojtech, E. (2006) Basic and Applied Ecology Volume 7: 296-306