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Caffeine natural pesticide, researcher says

For those who dismiss coffee as ''that foul brew,'' cocoa as ''kid's stuff,'' and tea as merely an excuse to ingest vast quantities of milk, sugar, and lemon juice, someone has just found a distasteful rubric to apply to all three: insecticide.

All of them contain caffeine. According to the findings of a Harvard Medical School researcher, caffeine turns out to be a naturally occurring insecticide.

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In order to determine effectiveness, safety, and feasibility of insecticides based on caffeine and its chemical relatives, several years of testing lie ahead before any can hit the market. But the discovery could help point the way to a new class of insecticides which is more discriminating and far gentler on the environment than what is often currently used.

In fact, toxicologists say they have already started down that path. Creeping into the market are innovative ''bio-rational'' compounds that accomplish their tasks by disrupting specific aspects of biological functions unique to insects. In theory, any other nearby organisms would be left alone.

Conventional insecticides, on the other hand, curb insect populations simply by poisoning them. It is an effective, though sometimes hazardous, procedure. The modern environmental movement sprang partly from concerns about problems associated with one such chemical, DDT.

''The problem with insecticides is that they are toxic to just about anything. Insects and vetebrates (a class that includes humans and all other mammals) have a lot of similarities,'' observes Harvard neurobiologist James Nathanson, whose findings were reported Friday in the journal Science.

Dr. Nathanson says his caffeine-based compound is not of the conventional variety because it destroys insects by zeroing in on their nervous systems. To achieve that precision, Dr. Nathanson combined caffeine-like substances with a hormone called octopamie that is found only in insects. When combined, he adds, the two act together on an insect's metabolism. So Nathanson cautions against dumping coffee grounds on the tomato patch because caffeine alone is, he says, ''not very potent.''

''A lot of insecticides were developed in a rather hit-or-miss way, we just knew whether they worked but not necessarily why,'' Nathanson observes. ''Now we're at the stage where we can build an insecticide with certainty from our knowledge of biological processes.''

In the meantime, the rest of the environment has theoretically been left uneffected. Caffeine and its chemical relatives, he found, is a defense mechanism that many plants have developed to ward off marauding insects. The leaves of tea and coffee plants, for instance, contain up to 2 percent of the substances.

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''These are natural compounds,'' Nathanson says of the caffeine and similar compounds in his insecticide. ''We already know a great deal (about caffeine), certainly more than most available insecticides.''

Nevertheless, there are some unknowns surrounding Dr. Nathanson's formula. Among them is what effect the concentrated doses of caffeine he has been working with - 10 to 15 times as strong as found in a cup of coffee - would have, distributed in the environment. There are questions, for example, about whether pure caffeine, as extracted from a tea leaf, would be biodegradable.

''What's going to happen if we spray high-concentration caffeine onto the ground from a crop duster?'' asks Sandra Marquandt of the National Coalition for the Misuse of Pesticides.

Still, experts say that custom-tailored pesticides such as Dr. Nathanson's experimental concoction are at the cutting edge of much insecticide research and may someday become commonplace. A handful of companies are already turning out a few types of bio-rational insecticides. ''Inevitably, this industry is going to be pushed in the direction of the bio-rational approach,'' says Alex Cross, who heads Zoecon Corporation, a Palo Alto, Calif., firm that pioneered the manufacture of selective insecticides. While he is quick to add that conventional pesticides have their place, he says that their current preeminence is temporary.''Environmental considerations will mandate it.''

But others say that day could be sometime off. It can take $15 million to $20 million to take a pesticide all the way from research to marketing stage. And by their nature, bio-rational compounds tend to be specialized. Nathanson's concoction, for instance, is targeted at tobacco hornworms, mealworms, and mosquito larvae.

''If you're a chemical company, and you're going to spend all that money, then you're going to want to cover a wide market,'' says University of Kentucky toxicologist H. Wyman Dorough. ''Is it worth $20 million to get the green-eyed bug in upper New York State?''