Long-term study: Bt maize cultivation without effect on earthworms

(25 May 2010) The results of a four-year study by ecologists in the USA and Switzerland indicate that earthworms are unaffected by the agriculture with genetically modified (GM) maize, even after years of cultivation. For most of the four strains of earthworm observed, it was of no importance whether Bt or conventional maize was grown on the field.

Bt varieties contain toxins against maize pests such as the corn root worm and represent 57 per cent of maize grown in the USA. Earthworms aid the decomposition of plant remains while mechanically loosening the surface of the soil, and both of these activities are important for soil fertility. Scientists from the universities of Minnesota, New York (both USA) and Neuchâtel (Switzerland) investigated the possible effects of Bt maize on earthworms present in cultivated fields, since these worms may ingest Bt proteins in plant remains and in root secretions.

Results from nine laboratory studies and four field trials already had indicated essentially no negative results for earthworms through the cultivation of Bt maize. However, two laboratory studies had indicated slightly slower earthworm growth, which may lead in the long term to smaller populations. Since this effect was observed only after 200 days, the four-year study was intended to observe the effects of several years of Bt maize cultivation. Three Bt maize varieties containing two Bt toxins were compared with conventional original lines.

Results of the study have been published in ‘Soil Biology and Biochemistry’. Test areas covered 1600 square metres and, in addition to the common earthworm (Lumbricus terrestris), three strains of the genus Aporrectodea were found in each area. Researchers measured earthworm biomass at different developmental stages and found no significant differences between the fields with Bt and with conventional maize.

Researchers recommend that these results be validated by investigations with other strains of earthworm, since the types of earthworm present in a cultivated field may depend on its geographical location.

Further information:

• Long-term study: Cultivation of Bt maize does not affect earthworms (GMO Safety)