Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, August 21, 1994 TAG: 9408220088
SECTION: HORIZON PAGE: D-1 EDITION: METRO
SOURCE: By JOHN BARBOUR ASSOCIATED PRESS
DATELINE: PATUXENT, MD. LENGTH: Long
Thirty springs ago, Rachel Carson died and left as her last will and testament a world where spring would never be silent again.
Her 1962 book, ``Silent Spring,'' which has sold 21/2 million copies and still sells some 35,000 a year, focused American attention on the profligate use of chemical pesticides.
Today, her principal targets - the chlorinated hydrocarbons, DDT, heptachlor, chlordane and others - are banned in the United States.
The eagles, the osprey and the brown pelicans that were killed outright or laid eggs so fragile that nesting parents crushed the weakened shells under their weight, are back in force.
Today they soar in the Patuxent National Refuge Area where Carson used to roam, over Chesapeake Bay and the Florida coast. Everywhere.
Robins sing again in East Lansing, Mich., the site of the original silent spring.
DDT had been sprayed on the elms of Michigan State University to halt Dutch elm disease. Wrote Carson:
``But soon it became evident that something was wrong. Dead and dying robins began to appear on the campus. Few birds were seen in their normal foraging activities or assembling in their roosts. Few nests were built; few young appeared.''
Spring was, indeed, falling silent, but this woman had an ear for the silence. Her evidence, written with simple eloquence, turned the nation around.
So after 30 springs, it's a good time to take stock. What has happened since Rachel Carson herself fell silent?
Gradually the banned chemicals are finally losing their toxicity in the soil they contaminated.
But perhaps more important, the chemists have had to yield to the research of ecologists and biologists. But did expedience, the use of quick-killing chemicals, give way to a more considered approach? Well, not quite.
Carson would have admired the research explosion her book touched off, but she would likely have been appalled at the slowness of practical application of that research. True, the most dangerous chemicals were banned in 1973.
Dr. Edward Knipling of the Agricultural Research Service, now 81 but vocal in retirement, says that insect pest management is still almost totally dependent on insecticides, perhaps as much as 90 percent. Others say 80 percent or less. Safer chemicals perhaps, but chemicals nevertheless.
Knipling and his team developed the sterile fly technology which has already eradicated the screw worm in the United States, Mexico and parts of Central America without chemicals. The sterile fly procedure - whereby male flies mate with females but do not reproduce the larval worm - has all but eliminated the flesh-eating hazard for warm-blooded animals from cattle to children.
Says Knipling, ``The philosophy has been wrong in my opinion. People [growers] wait until they have to do something. They don't think in terms of protective measures. I think if the philosophy of pest control were based as strongly on prevention as it is in the prevention of human diseases, we'd be much better off.''
As it is for 95 percent of the pests, growers wait until a pest strikes that could destroy or damage a crop in a week. So they reach for the expedient solution - chemical pesticides - and begin seeing dead insects the next day. Natural controls are more subtle and slower.
Dr. James L. Krysan, who heads the national program for biocontrol at the Agricultural Research Service, says, ``At the time of Rachel Carson, most of our research was aimed at improving DDT. Now at least 80 percent of the ARS budget for pest control is for alternatives to chemical pesticides, making plants more pest-resistant, developing viruses, finding the natural diseases of insects and making those more effective.''
Today the quandary is more economic than scientific. In many situations the natural armament is out there, but farmers and pesticide manufacturers choose the quick or short course. At the same time, the broadside chemicals kill both pest and natural enemy.
Dr. Richard S. Soper, assistant administrator for ARS' International Research, says that in classical biocontrol, where a natural enemy is introduced to the pest, there is ``no profit motive'' for producers of the biocontrol agent. Once the predator or parasite is released and becomes established in the pest population, ``there's no resale because it does its thing without any further intervention.''
So production of these agents must fall to government.
Progress is slow, but the weapons are there and most are remarkable.
Since 1905, the Department of Agriculture has been importing parasites and predators of the elm leaf beetle, the alfalfa and clover leaf beetles, and the brown tail and gypsy moths. And while home gardeners were still using chlordane against the Japanese beetle, there was available the bacillus popilliae or milky spore disease which even today suppresses the beetle.
Another nonchemical agent still on the market is bacillus thuringiensis, Bt, which produces a toxin effective against, among other things, the sugar beet maggot and the Colorado potato beetle that attacks tomato plants and eggplants.
During World War II, American troops and refugees alike were infested by body lice. And lice carry typhus. The U.S. Army needed an answer and quickly.
Chemical companies sent in hundreds of chemical samples and one, the Geigy Co. of Switzerland, offered a packet of something which came to be called DDT. It was tested on 25 volunteers at an Agriculture Department facility in Orlando, Fla., and proved to be twice as lasting against lice as anything else. Almost immediately, millions of 2-ounce cans were on their way to war and were used on millions of men, women and children.
Furthermore, DDT and its kin were effective against almost everything: mosquitoes, houseflies, boll weevils, bedbugs. They were chemicals of broad virulence, and they killed not only pests, but the natural enemies of pests.
Unfortunately they also were long-lasting in the soil where they lodged in earthworms, which robins consumed at the rate of a dozen a day, thereby affecting the birds. They lodged in eagles, which consumed them from smaller prey, thereby weakening the eagle eggs. They lodged in the fat tissue of innumerable species because they are soluble in fat. They lodged in the fatty organs, like the livers, of human beings.
Such was Carson's alarm. And then, too, there were signs that the pests were developing resistance to the chemicals.
Consider the apple in the Northwest. The coddling moth enjoys laying its eggs in apple blossoms, from which apples develop. As the apple develops, so does the larvae, the literal worm in the apple.
About 1970, Krysan points out, the coddling moth was one of the first insects for which a sex hormone was identified, but in such tiny quantities extracted from the moths that it was useless, until it was synthesized chemically.
Now after a number of smaller-scale tests, it is being sown on thousands of acres where it befuddles the sexual appetites of male moths and greatly lessens procreation, a progressive experience generation after generation.
In California, the coddling moth is developing resistance to chemical insecticides, which often happens, and in Washington state growers have turned around to improve their product.
There are also species-specific parasites for grape insects, for the Oriental fruit moth in peaches, the tomato pin worm in Mexico, the pink boll worm in Arizona.
There is no pest anywhere, says Dr. James L. Vaughn, research leader at ARS' Insect Biocontrol Laboratory, that doesn't have a natural enemy.
The male sterilization technique pioneered by Knipling is still being used against the Mediterranean fruit fly. And it costs about $34 million a year to maintain the sterile battle line against the screw worm fly, with the aim of driving the pest-free zone to the isthmus of Panama.
``It saves about $400 million a year,'' Krysan says, ``plus the human misery where many children are attacked by screw worm flies.''
The fly lays its eggs in open wounds and the larvae create a festering wound. The larvae, hundreds of them in a wound, have tusk-like mandibles which rasp off the flesh.
Public enemy No. 1 is still the corn root worm, which costs farmers $1 billion a year, year after year.
``As I understand it,'' Krysan says, ``it is still the champion when it comes to pesticide use in this country. There is more pesticide put down for corn root worm than any other pest. ... The females lay their eggs and in the spring they hatch and the larvae feed on the roots of the corn next year. So if you plant corn every year in the same place, you have a terrible pest problem.''
Farmers got smart and rotated their corn crops and that worked for a while. But now scientists have found that even while rotating soybeans and corn the northern variety of the corn worm has somehow learned to stay dormant for at least two years, the same way it developed resistance to chlorinated hydrocarbons. Some smart worm.
One of the greatest allies of the pest fighters are tiny wasps that lay their eggs in various forms of worms and weevils that attack everything from corn to cotton.
``There are marvelous ways to think about dealing with pests specifically,'' Krysan says. But to get there, ARS scientists at Gainsville, Fla., are learning every intimate detail of a pest's life.
Led by their sex hormone or pheromone research, scientists are looking into how insects and plants communicate usually by sensing subtle chemical emissions.
To their surprise they found that when the army worm feeds on corn, the corn reacts to the salivary secretions of the worm by emitting an odor. No other kind of wound causes this effect, only the saliva of the voracious worm.
An insignificant observation at first. But when the odor travels through the corn field, it attracts a natural enemy of the army worm, a tiny wasp which homes in on the worm in the corn stalk.
``We are going to have to take these things into account when we breed corn or cotton, so that we keep some of the corn's natural protection against pests,'' Krysan says. ``We didn't have a clue 30 years ago about pheromones or that plants and insects communicate with each other in these subtle ways with chemicals. It wasn't part of our vocabulary or our thinking.
``We can't go on attacking pests in broad ways, and that's basically what Rachel Carson saw.''
In the thousands of acres of this part of Maryland, the federal government keeps track of the wildlife and the plant life that are part of the national heritage. In fact, they are thinking here about naming a new visitors center after Rachel Carson.
Down the road in Beltsville is an even stronger reminder. Barren acres bear signs which say:
``Entry into fields prohibited.
``Fields may have received Pesticides.''
by CNB