Earthworms, which play a key role in biogeochemical processes in soil ecosystems, could be negatively affected by the cultivation of transgenic Bt crops. Studies to date have found few effects of Bt maize on earthworm species. If adverse effects occur, they are likely to be chronic or sub-lethal and expressed over large spatial and temporal scales. Our objective in the present study was to investigate potential effects on earthworm populations in soil cultivated with Bt maize in a large multiple-year field study. We surveyed the earthworm populations in 0.16-ha experimental field plots of two varieties of Cry1Ab Bt maize, one variety of Cry3Bb1 Bt maize, and three non-transgenic control varieties cultivated for four years. Four earthworm species were found in our sample: Aporrectodea caliginosa, Aporrectodea trapezoides, Aporrectodea tuberculata (collectively, the A. caliginosa species complex), and Lumbricus terrestris. We found no significant differences in the biomass of juveniles and adults for all four species between Bt and non-Bt maize varieties. From this and previous studies, we conclude that the effects of Cry1Ab and Cry3Bb1 Bt maize on the A. caliginosa species complex and L. terrestris are small. Nonetheless, general conclusions about the effects of Bt maize on earthworm populations are not warranted due to the small number of species tested. In future laboratory studies, earthworm species should be selected according to their association with a Bt crop and the impact of that species to valued soil ecosystem processes.
Bibliographical noteFunding Information:
This study was partially supported by an IFAFS grant from the US Department of Agriculture to DAA, an NRI grant from the US Department of Agriculture to GS and DAA, a PBBEA post-doctoral fellowship (#101094) from the Swiss National Science Foundation to CZ, and an IGERT grant from the US National Science Foundation to the University of Minnesota. The opinions expressed herein are not necessarily those of the USDA or NSF. We thank Andy Holdsworth for assistance with species identification keys and the mustard extraction technique. We thank Nick Ellering, Ozge Goktepe, Yang Hu, Chih-Ming Hung, Matt Korthauer, Marie LaVictoire, Amy McIntyre, Welile Mhlanga, Beth Pettitt, and Mary Wood for valuable assistance with field and laboratory work. Patricia Oikawa provided helpful comments on an early draft. Dr. Graham Head also provided helpful comments on an early draft as part of a Monsanto Technology Agreement (MTA). This study fully complies with the terms of the MTA.
- Bacillus thuringiensis
- Genetically modified crops
- Non-target effects
- Transgenic crops