Rootworms attacking engineered corn plants

Scientists fear hybrid losing effectiveness

Genetically modified corn produces a toxin that poisons rootworms, but it might be losing that ability more rapidly than expected.

One of the nation's most widely planted crops -- a genetically engineered corn plant that makes its own insecticide -- may be losing its effectiveness because a major pest appears to be developing resistance more quickly than expected.

The problem is isolated. But scientists fear potentially risky farming practices could be blunting the hybrid's sophisticated weaponry.

When it was introduced in 2003, Bt corn seemed like a dream: It would allow growers to bring in bountiful harvests using fewer chemicals because the corn naturally produces a toxin that poisons western corn rootworms. The hybrid was such a swift success that it and similar varieties now account for 65 percent of all U.S. corn acres.

But over the last few summers, rootworms have feasted on the roots of Bt corn in parts of four Midwestern states, suggesting that some of the insects are becoming resistant to the crop's pest-fighting powers.

Scientists say the problem could be partly the result of farmers who've planted Bt corn year after year in the same fields. Most farmers rotate corn with other crops in a practice long used to curb the spread of pests.

A scientist recently published findings concluding that rootworms in a handful of Bt cornfields in Iowa had evolved an ability to survive the corn's formidable defenses.

Similar crop damage has been seen in parts of Illinois, Minnesota, and Nebraska, but researchers are still investigating whether rootworms capable of surviving the Bt toxin were the cause.