Bt-corn is genetically engineered to express toxins that will protect corn against lepidopteran pests.

Because Bt corn is widely planted, it is important to evaluate the potential risks of the Bt protein to non-target organisms, such as earthworms.

Earthworms are important to the aeration and nutritional content of soils; they are also important to corn grown in reduced tillage practices, since earthworms can maintain and improve soil physical conditions.

Only a few studies have dealt with the effects of Bt protein on earthworms, and Maria Laura Vercesi and colleagues of National Environmental Research Institute, Denmark add their own research to the tally as they ask: �Can Bacillus thuringiensis (Bt) corn residues and Bt-corn plants affect life-history traits in the earthworm Aporrectodea caliginosa?� In a recent issue of Applied Soil Ecology, the authors report the effects of Bt-corn on survival, reproduction, and growth of the most widespread earthworm species in temperate agricultural soils.

Researchers tested the effects of finely ground Bt corn cultivar MEB307 leaves in soil on A. caliginosa, including concentrations that would be considered �worst case scenario.� They also tested the effects of Bt protein on earthworms by raising juveniles in soils in potted corn plants. After statistical analysis of their results, researchers recorded the following: 1) no earthworm adults died in the reproduction experiments with finely ground corn leaves; 2) there were no significant differences in juvenile growth curves between Bt and non-Bt exposed earthworms, but earthworm growth was drastically reduced in non-Bt plants treated with benomyl, a fungicide toxic to earthworms; and 3) there was slightly reduced cocoon hatchability of earthworms exposed to Bt corn.

Despite the decreased hatchability, scientists concluded that Bt corn residues had no detrimental effects on growth or development in A. caliginosa. This was because scientists added fresh Bt-corn material to the soil every 28 days; Bt-protein in corn leaves is degraded with a half-life of about 20-40 days.

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