The United States is planning to import a moth from Greece that munches on the roots of the knapweed. The plants flourish on rangeland in the Pacific Northwest and are mildly toxic to cows. By controlling the weeds, officials at the US Department of Agriculture hope to keep the ranges open to cattle grazing.
This is just one example of the search for viable alternatives to chemical pesticides. In the 25 years since Rachel Carson wrote ``Silent Spring,'' agricultural pesticides have mushroomed into an estimated $18 billion-a-year global industry. Farm use accounts for more than three-quarters of all the pesticides consumed in the US.
And pesticides are integral to modern agriculture.
For example, many farmers no longer rotate crops the way their ancestors did. Alternating crops tends to keep many pests under control naturally, since insects that feed on a certain grain starve during the season that crop is not planted. ``A lot of alternative pest control strategies are nothing more than good old-fashioned farming methods,'' says Garth Youngberg, executive director of the Institute for Alternative Agriculture in Greenbelt, Md.
Mr. Youngberg estimates that there are between 30,000 to 40,000 farms in the US that use little or no pesticides.
``But whether biotechnology is beneficial or not will depend on where the priorities are put,'' Youngberg says.
And these are not just the ``back to nature'' types. A growing number of mainstream farmers have begun to question the farming techniques they adopted in recent decades.
As the farm economy has crumbled, farmers have sought to cut their use of expensive chemicals. In addition, there is growing recognition among farmers that agricultural pesticides can contaminate ground water and cause health problems.
Some also question the long-term effectiveness of the chemicals. The National Academy of Sciences calculates that 447 insects had developed some sort of resistance to at least one pesticide by 1984. More than a dozen important insects, including the highly destructive Colorado potato beetle, are now resistant to all five major classes of insecticides.
One popular approach to cutting back on pesticides is known as ``integrated pest management.'' Although the concept is defined many ways, it generally means mixing various pest-inhibiting farming techniques with a minimum reliance on chemicals. Dick Thompson, a farmer from Boone, Iowa, stopped using most pesticides on his land 20 years ago. Although he relies on many classical techniques, such as crop rotation, he also integrates relatively new innovations.
For example, Mr. Thompson uses ``ridge tillage,'' in which crops are planted on mounded ridges in the soil. By disturbing only the top during planting, he has less trouble with weeds and erosion. Thompson says he continues to turn a profit on his crops.
Carrying the search for alternatives a step further - such as importing weed-eating moths - is known as biological pest control. The first such control program was launched in the 1880s, when California's citrus industry was saved from an infestation of scale insects by the importation of vedalia beetles from Australia.
``There's a long list of problems that could be solved through bio-control, but they aren't,'' says Roy Van Driesche, an entomologist at the University of Massachusetts. In many cases, he says, the search for biological solutions is used only when all else fails.
The Department of Agriculture has about 220 scientists working on aspects of biological control through its Agricultural Research Service. But they are sprinkled across a number of programs and offices. An effort is now under way to establish a comprehensive program.
Meanwhile, biotechnology is being touted as a potential source of innovations in pest control. For example, new plants might be developed that are naturally resistant to pests.
Some observers worry that chemical companies - which have invested heavily in biotechnology - could use it to expand the market for pesticides. For example, work is already under way to develop plants that are resistant to chemical herbicides. One of the problems with herbicides is that they often damage the crops along with the weeds. A herbicide-resistant plant would allow farmers to slosh on even more chemicals.
The underlying question, however, is whether alternatives to chemical pesticides will ever command more than a small share of the market. If the ideas are good, why are they not being used more broadly? Part of the reason is money. To be widely used, alternative pest control techniques must be cost effective. But the large chemical companies have traditionally supported much of the agricultural research done at US universities. Government research is also skewed toward chemical solutions.
The biggest stumbling block, however, is popular perceptions and practices.
``People don't change until they have to,'' says farmer Thompson. In Iowa, for example, the state legislature has begun looking closely at such issues as ground-water contamination and is pressuring for changes in farming practices.
Last in a series. Previous stories ran July 20 and 21.