To preserve the ``health of the planet,'' environmentalists advocate concern for the whole ecosystem, not just endangered species. Indeed, the whole ecosystem is affected by measures designed to ``help'' one particular species. Among the unintended beneficiaries, the most important is the Anopheles mosquito.

At a recent meeting of the Pima County Medical Society, Stephen Hoffman, President of Hawk Watch International, showed a slide of an egg with an obviously defective shell. Q.E.D. Res Ipse Loquitur (the thing speaks for itself). It is time for places like Mexico to follow the enlightened lead of the United States and ban that evil carcinogenic chlorinated hydrocarbon before all the hawks die.

``There are other ways to control malaria,'' said Mr. Hoffman.

Public health officials boast of our success in controlling the plagues of infectious diseases that once decimated human populations. This success, for many diseases, depends on the control of arthropod vectors such as insects, lice, and ticks.

If we were asked to think of chemicals that have saved millions of human lives, penicillin might come to mind. But no drug comes close to rivaling DDT (dichlorodiphenyl-trichloroethane). The National Academy of Sciences estimated that as of 1981, ``DDT has prevented 500 million deaths (human) that would otherwise have been inevitable.''

Malaria has claimed more human victims over the centuries than all other diseases combined. In the 1940s, India and Pakistan suffered more than 75 million cases with 5 to 7 million deaths every year. A WHO program that relied principally upon DDT reduced the incidence to 100,000 per year. Within a decade, the life span of the average Indian increased by more than 15 years. Vast areas of India that had been uninhabitable were planted with subtropical strains of wheat and short-stem strains of rice. This ``Green Revolution'' raised India's grain production to well over 100 million metric tons.

After DDT was banned, the toll of malaria increased to 6 million per year in India, Pakistan, and Bangladesh. The environment was restored to its original condition─the mosquitoes moved back, and the farmers were forced out.

Malaria is also increasing in the United States. In the early 1960s, before infected veterans began to return from Vietnam, the incidence was about 0.05 per 100,000. In the 1980s, it was around 0.5 per 100,000, a tenfold increase. (DDT was banned in 1972.) While many of the cases are in foreign immigrants, indigenous cases are also occurring.

Yes, there are other methods of controlling malaria. Other pesticides are about ten times as expensive and require more frequent application. They are more toxic, and many of them have also been banned. Draining swamps can be effective, but swamps are protected wetlands. Draining a rice paddy defeats the purpose.

Many other arthropod-borne diseases are also experiencing a resurgence. These include onchocerciasis (river blindness), carried by the black fly Simulium; filariasis (elephantiasis), carried by mosquitoes; and visceral leishmaniasis (Kala-azar), carried by the sand fly Phlebotomus. The last could establish a presence in the United States; veterans of the Gulf War are being rejected as blood donors because of the possibility of this disease. In the United States, the incidence of Rocky Mountain spotted fever (tick-borne typhus) has increased from about 0.14 per 100,000 in the 1960s to about 0.37 per 100,000 in the 1980s. Encephalitis, an untreatable disease that frequently causes death or lifelong neurologic disability, has also increased recently.

Head lice are not reportable, so statistics are not available. In our anecdotal experience, this problem has become considerably more frequent in Arizona now that Mexican workers do not pass through the DDT dusting station at the border.

Besides human beings, many other living things have been protected by DDT and other pesticides, notably cotton and timber. The bark beetle, which is still out of control, probably destroys twenty times as many trees as fire does.

The environmentalists' choice of DDT as the premier environmental poison is ironic. Paul Muller, the chemist who discovered DDT, received the Nobel Prize for finding a substitute for the numerous toxic chemicals that previously were used for pest control: lead, arsenic, mercury, and fluorine. No toxic effects were observed in the more than 600 million persons living in homes repeatedly sprayed with DDT, or in the thousands of individuals who have had their skin dusted with it, or in volunteers who ate 35 mg/day for many months. (The average daily intake of the US population was 0.065 mg/day in 1968.)

There is no evidence that DDT is carcinogenic, although some strains of mice developed benign liver ``tumors'' when exposed to the maximum tolerated levels (100,000 times higher than pesticide residues).

It is possible to kill wildlife with DDT through very poorly planned spraying programs, for example, by wiping out their entire food supply. It is also possible to commit suicide by ingesting a monumental overdose.

What about the hawks? Hawks were declining in number for 50 years before DDT was widely used in the US, but were increasing in the 1960s. Eggshell thinning has a differential diagnosis; one cause is frightening the bird so that it lays the egg prematurely. At least one experiment actually showed that more birds hatched when their mothers were fed DDT. If DDT did cause eggshell thinning in certain birds, the effect was restricted to a very small geographic area.

It is difficult to fathom why DDT, of all chemicals, was totally banned by the Environmental Protection Agency. The decision was clearly political, not scientific. Possibly, it was done to demonstrate the power of the fledgling agency by setting an example. If the EPA administrator could ban DDT (without even reading the transcripts of the hearings), he could ban anything.

Why did environmental groups focus their activism on this beneficial and largely innocuous chemical, demanding a ban that some scientists described as ``genocidal'' in its impact? Dr. Charles Wurster, chief scientist for the Environmental Defense Fund, responded to a reporter's question by saying that there were too many people and ``this was as good a way to get rid of them as any.''

Should you stockpile DDT for your bomb shelter? Forget it. Although the US government cannot stop Libya or North Korea from making nerve gas, its ban on domestic agricultural and industrial chemicals is quite effective. Unlike some other chemicals (such as marijuana, methamphetamine, and cocaine), DDT offers no profit incentive. In 1968, one pound of DDT─enough to dust one acre─cost 17.5 cents.

You might want to add antimalarials to your list of drugs.