Can Bacillus thuringiensis (Bt) corn residues and Bt-corn plants affect life-history traits in the earthworm Aporrectodea caliginosa?

Bt-corn is genetically engineered to express proteins from the common soil bacterium Bacillus thuringiensis which presents specific toxicity to targeted insect pests. One type of Bt-corn expresses the Cry1Ab protein that provides protection against certain lepidopteran pests, mainly the European corn borer (Ostrinia nubilalis) and the Mediterranean stalk borer (Sesamia nonagroides). Vast areas of agricultural soils worldwide are grown with transgenic Bt-corn. With such widespread use of Bt-corn, it is important to evaluate the potential risks of Bt-protein to non-target organisms in agro-ecosystems such as earthworms. In this study, we investigated the effects of Bt-corn on important life-history traits (survival, reproduction and growth) of the earthworm Aporrectodea caliginosa under various experimental conditions. Finely ground Bt-corn leaves added to soil had no deleterious effects on survival, growth, development or reproduction in A. caliginosa, even in high concentrations that could be considered as a worst-case scenario. Also, growth of juvenile A. caliginosa was unaffected when worms were kept in pots with a growing Bt-corn plant. Only when considering cocoon hatchability did we see a slight, but statistically significant, negative effect of Bt-corn residues. The implications of these results for risk assessment of Bt-corn are discussed.