PRESTON, MINN. - Danny Serfling knew he was in trouble in July. Tiny white worms in the soil had eaten away the anchoring roots on half of his corn, and in one big storm last summer, the stalks toppled like sticks.

"All the corn around here went flat -- from Spring Valley to Mabel," said Serfling, who farms a few hundred acres here in southeastern Minnesota. He waved a tattooed arm toward stubbled hills that rolled away to the gray October sky, resigned to the next step. "We will have to use more insecticide," he said.

It is what scientists and environmentalists regard as one of nature's great ironies: Fifteen years ago, genetically engineered seeds promised to reduce the amount of poisons used on the land, but today they are forcing farmers to use more -- and sometimes more toxic -- chemicals to protect their crops.

Why? Because pests have done what nature always does -- adapt. Just as some bacteria have become resistant to antibiotic drugs, a growing number of superweeds and superbugs in the nation's farm fields are proving invulnerable to the tons of pesticides that go hand in hand with genetically modified seeds.

The rising tide of pesticides is alarming many scientists and environmentalists about their effect on what's left of the North American prairie ecosystem, which survives in and around the vast "green deserts" of row crops that now stretch across the Upper Midwest.

"There are now 80 million acres of treated corn," said Eric Mader, an ecologist with the Xerces Society for Invertebrate Conservation. "That's a huge volume of pesticides applied for one crop."

What's next, they say, is even worse. To combat the growing wave of resistant weeds and bugs, biotech companies like Monsanto and Dow Chemical Company are poised to launch a whole new arsenal of genetically modified seeds that will accelerate the chemical warfare. Some are designed for use with older, more toxic herbicides that scientists say pose an even greater risk to the environment and human health.

The biotech companies say they will educate farmers and extension agents on how to minimize the health and environmental risks, and that the multiple genetic weapons contained in the new seeds will make it impossible for pests to develop resistance.

"We believe this can be managed," said Rick Cole, a weed management technical lead for Monsanto.

Still, a rising chorus of protest from environmental and agricultural scientists says it won't work. Nature, they say, will simply adapt again.

"It makes about as much sense as pouring gas on a fire to put it out," said Charles Benbrook, a researcher at Washington State University. "It is going to lead to the exact same problem and a substantial increase in much less benign herbicides."

Genetic revolution

Fifteen years ago, genetically modified seeds revolutionized farming.

Monsanto introduced the first, a variety of soybean that was immune to the herbicide Roundup. Suddenly, life got a lot easier for farmers. They could spray their fields once or twice with Roundup -- prized because it kills virtually all plants but is largely benign to animals and people -- and then plant their crops. And they no longer had to till the land to get rid of pesky weeds, greatly reducing the potential for soil erosion.

Roundup-ready cotton, corn, canola, alfalfa and sugar beets followed in quick succession, making Roundup one of the most widely used herbicides in the world. "Farmers were very quick to adopt it," said Cole.

A few years later, Monsanto introduced the next genetic advance -- corn that contained its own insecticide, a protein called Bt that is poisonous to insects. Bt corn also was viewed as an environmental boon, because it was highly targeted -- it killed only the insects, like rootworm and corn borer, that ate the corn. That meant far less aerial spraying and dousing soils with poisons that killed everything from worms to birds.

And it worked. The U.S. Department of Agriculture reported that per-acre use of pesticides on corn, soybeans and cotton declined by several million pounds per year, and soil tillage declined, as well.

The new technology paid off for Minnesota and other Midwestern states. In 2011, Minnesota farmers produced $10 billion worth of corn and soybeans, according to the USDA. On top of that, the ethanol industry added nearly another billion dollars to Minnesota's economy.

But the genetic breakthroughs brought sweeping changes across the landscape. Today, a third of Minnesota is planted with just two genetically modified species -- corn and soybeans -- and in some other states, it's far more.

Meanwhile, acreage devoted to such non-genetically modified crops as wheat, sunflowers and barley has plummeted by 50 to 90 percent.

In short, Midwestern agriculture quickly evolved into a vast, efficient system that is much easier to farm but is "biologically simple," said Doug Gurian-Sherman, a senior scientist with the Union of Concerned Scientists, and a specialist on biotech agriculture.