Native to India and Burma, neem is a botanical cousin of mahogany. It is tall and spreading like an oak and bears masses of honey-scented white flowers like a locust. Its complex foliage resembles that of walnut or ash, and its swollen fruits look much like olives. It is seldom leafless, and the shade it imparts throughout the year is a major reason why it is prized in India. The Subcontinent contains an estimated 18 million neem trees, most of them lined along roadsides or clustered around markets or backyards to provide relief from the sun.
Under normal circumstances neem's seeds are viable for only a few weeks, but earlier this century people somehow managed to introduce this Indian tree to West Africa, where it has since grown well. They probably expected neem to be useful only as a source of shade and medicinals—especially for malaria—but in Ghana it has become the leading producer of firewood for the densely populated Accra Plains, and in countries from Somalia to Mauritania it is a leading candidate for helping halt the southward spread of the Sahara Desert.
This century, people took neem seed to other parts of the world, where the tree has also performed well. Near Mecca, for example, a Saudi philanthropist planted a forest of 50,000 neems to shade and comfort the two million pilgrims who camp each year on the Plains of Arafat (a holy place where the prophet Muhammad is said to have bidden farewell to his followers). And in the last decade neem has been introduced into the Caribbean, where it is being used to help reforest several nations. Neem is already a major tree species in Haiti, for instance.
But neem is far more than a tough tree that grows vigorously in difficult sites. Among its many benefits, the one that is most unusual and immediately practical is the control of farm and household pests. Some entomologists now conclude that neem has such remarkable powers for controlling insects that it will usher in a new era in safe,
natural pesticides.1 Extracts from its extremely bitter seeds and leaves may, in fact, be the ideal insecticides: they attack many pestiferous species; they seem to leave people, animals, and beneficial insects unharmed; they are biodegradable; and they appear unlikely to quickly lose their potency to a buildup of genetic resistance in the pests. All in all, neem seems likely to provide nontoxic and long-lived replacements for some of today's most suspect synthetic pesticides.
That neem can foil certain insect pests is not news to Asians. For centuries, India's farmers have known that the trees withstand the periodic infestations of locusts. Indian scientists took up neem research as far back as the 1920s, but their work was little appreciated elsewhere until 1959 when a German entomologist witnessed a locust plague in the Sudan. During this onslaught of billions of winged marauders, Heinrich Schmutterer noticed that neem trees were the only green things left standing. On closer investigation, he saw that although the locusts settled on the trees in swarms, they always left without feeding. To find out why, he and his students have studied the components of neem ever since.
Schmutterer's work (as well as a 1962 article by three Indian scientists showing that neem extracts applied to vegetable crops would repel locusts) spawned a growing amount of lively research. This, in turn, led to three international neem conferences, several neem workshops and symposia, a neem newsletter, and rising enthusiasm in the scientific community. By 1991, several hundred researchers in at least a dozen countries were studying various aspects of neem and its products.
Like most plants, neem deploys internal chemical defenses to protect itself against leaf-chewing insects. Its chemical weapons are extraordinary, however. In tests over the last decade, entomologists have found that neem materials can affect more than 200 insect species as well as some mites, nematodes, fungi, bacteria, and even a few viruses. The tests have included several dozen serious farm and household pests—Mexican bean beetles, Colorado potato beetles, locusts, grasshoppers, tobacco budworms, and six species of cockroaches, for example. Success has also been reported on cotton and tobacco pests in India, Israel, and the United States; on cabbage pests in Togo, Dominican Republic, and Mauritius; on rice pests in the Philippines; and on coffee bugs in Kenya. And it is not just the living
Researchers at the U.S. Department of Agriculture have been studying neem since 1972. In laboratory experiments, they have found that the plant's ingredients foil even some of America's most voracious garden pests. For instance, in one trial each half of several soybean leaves was sprayed with neem extracts and placed in a container with Japanese beetles. The treated halves remained untouched, but within 48 hours the other halves were consumed right down to their woody veins. In fact, the Japanese beetles died rather than eat even tiny amounts of neem-treated leaf tissue. In field tests, neem materials have yielded similarly promising results. For instance, in one test in Ohio, soybeans sprayed with neem extract stayed untouched for up to 14 days; untreated plants in the same field were chewed to pieces by various species of insects, seemingly overnight.
Neem contains several active ingredients, and they act in different ways under different circumstances. These compounds bear no resemblance to the chemicals in today's synthetic insecticides. Chemically, they are distant relatives of steroidal compounds, which include cortisone, birth-control pills, and many valuable pharmaceuticals. Composed only of carbon, hydrogen, and oxygen, they have no atoms of chlorine, phosphorus, sulfur, or nitrogen (such as are commonly found in synthetic pesticides). Their mode of action is thus also quite different.
Neem products are unique in that (at least for most insects) they are not outright killers. Instead, they alter an insect's behavior or life processes in ways that can be extremely subtle. Eventually, however, the insect can no longer feed or breed or metamorphose, and can cause no further damage.
For example, one outstanding neem component, azadirachtin, disrupts the metamorphosis of insect larvae. By inhibiting molting, it keeps the larvae from developing into pupae, and they die without producing a new generation. In addition, azadirachtin is frequently so repugnant to insects that scores of different leaf-chewing species—even ones that normally strip everything living from plants—will starve to death rather than touch plants that carry traces of it.
Another neem substance, salannin, is a similarly powerful repellent. It also stops many insects from touching even the plants they normally find most delectable. Indeed, it deters certain biting insects more effectively than the synthetic chemical called "DEET" (N,N-diethylm-toluamide), which is now found in hundreds of consumer insect repellents.
To obtain the insecticides from this tree is simple (at least in
principle). The leaves or seeds are merely crushed and steeped in water, alcohol, or other solvents. For some purposes, the resulting extracts can be used without further refinement. These pesticidal "cocktails," containing 4 major and perhaps 20 minor active compounds, can be astonishingly effective. In concentrations of less than one-tenth of a part per million, they affect certain insects dramatically. In trials in The Gambia, for example, these crude neem extracts compared favorably with the synthetic insecticide malathion in their effects on some of the pests of vegetable crops. In Nigeria, they equaled the effectiveness of DDT, Dieldrin, and other insecticides. And elsewhere in the world these plant products have often showed results as good as those of standard pesticides.
The extracts from neem seeds can also be purified and the most effective ingredients isolated from the rest of the mix. This process allows standardization and uniform formulations that can be produced for commercial use in even the world's most sophisticated pesticide markets.
Whatever the mixture or formulation, neem-based products display several remarkable qualities. For example, although pests can become tolerant to a single toxic chemical such as malathion, it seems unlikely
Desert locust. After four locust nymphs (fifth instar) were treated with neem oil, three got only halfway out of terminal molt and died. The fourth molted completely but had fatal deformities. (H. Schmutterer)
Colorado potato beetle. These neem-treated specimens have malformed wings that can neither function in flight nor fold flat. In addition, these specimens are sterile. (E.B. Radcliffe)
Grasshopper. After treating a third-instar nymph of the variegated grasshopper, Zonocerus variegatus, the adult emerged with no antennae and defective wings. (H. Schmutterer)
Gypsy moth. Applying neem extracts to the larva (third instar) resulted in an incomplete molt. The old skin is still attached to the back of the body, making the insect unable to function. (H. Schmutterer)
Another valuable quality is that some neem compounds act as systemic agents in certain plant species. That is, they are absorbed by, and transported throughout, the plants. In such cases, aqueous neem extracts can merely be sprinkled on the soil. The ingredients are then absorbed by the roots, pass up through the stems, and perfuse the upper parts of the plant. In this way, crops become protected from within. In trials, the leaves and stems of wheat, barley, rice, sugarcane, tomatoes, cotton, and chrysanthemums have been protected from certain types of damaging insects for 10 weeks in this way.
Because systemic materials are inside the plant, they cannot be washed off by rain. Nor can they harm bees, predacious insects, and other organisms that do not chew plant tissue. Even new growth that occurs following the treatment may be protected. (In the case of conventional sprayed-on chemicals, on the other hand, new growth is usually vulnerable to insects.)
Perhaps the most important quality is that neem products appear to have little or no toxicity to warm-blooded animals. Birds and bats eat the sweet pulp of the fruits of neem trees without apparent ill effects. In fact, neem fruits are a main part of their diets in some locations, such as on Ghana's Accra Plains. When neem-seed extracts were brushed on the skins of rats, the animals' blood showed no abnormalities; indeed, the treated rats ate more food and gained more weight than the untreated ones.
This safety to mammals apparently extends to people. The deaths of a few young children in Malaysia in the 1980s have been linked to the doses of neem-seed oil forced on them by their parents. (Like the previous use of castor oil in the Western world, neem oil in Asia is considered a cure-all for some childhood illnesses.) However, other than this, no hazard has been documented under conditions of normal usage. For one thing, neem extracts show no mutagenicity in the Ames test, which detects potential carcinogens. For another, people in India have been adding neem leaves to their grain stores for centuries to keep weevils away. Thus, for many generations millions have been eating traces of neem on a daily basis.
Certain neem products may even benefit human health. The seeds and leaves contain compounds with demonstrated antiseptic, antiviral, and antifungal activity. There are also hints that neem has anti-
For dental hygiene, especially, neem could prove valuable. Despite a general lack of toothpaste and toothbrushes, most people in India have bright, healthy teeth, and dental researchers usually attribute this to "chewsticks." Every morning, millions of Indians break off a twig, chew the end into a brush like form, and scrub their teeth and gums. The most popular are the twigs from neem, and the selection seems to have a scientific basis. Research has shown, for example, that compounds in neem bark are strongly antiseptic. Also, tests in
Moreover, researchers have recently found that neem might be able to play a part in controlling population growth. Materials from the seeds have been shown to have contraceptive properties. The oil is a strong spermicide and, when used intravaginally, has proven effective in reducing the birth rate in laboratory animals. A recent test involving the wives of more than 20 Indian Army personnel has further demonstrated its effectiveness.
Other neem compounds show early promise as the long-sought oral birth-control pill for men. This is just an intriguing hint at present; however, in exploratory trials they reduced fertility in male monkeys and a variety of other male mammals without inhibiting sperm production. In addition, the effects seemed to be temporary, which would be a big selling point that could help its rapid and widespread adoption.
All of this is potentially of vital importance for the world's poorest countries, many of which have high rates of population growth, severe problems with various agricultural pests, and a widespread lack of even basic medicine. The neem tree will grow in many Third World regions, and it can grow on certain marginal lands where it will not compete with food crops. Thus, it could bring good health and better crop yields within the reach of farmers too poor to buy pharmaceuticals or farm chemicals. It makes feasible the concept of producing one's own pesticide because the active materials can be extracted from the seeds, even at the farm or village level. Extracting the seeds requires no special skills or sophisticated machinery, and the resulting products can be applied using low-technology methods.
This possibility is significant because most developing countries are in the tropics, where year-round warmth often allows pest populations to build to unacceptable levels. The problems attendant on using synthetic pesticides, therefore, are particularly severe in the Third World. For instance, the World Health Organization attributes 20,000 deaths and more than a million illnesses each year to pesticides mishandled or used to excess. In addition, because the pests breed year-round, mutational resistance builds up much more quickly in the tropics than in lands having winter seasons.
Neem also seems particularly appropriate for developing country use because it is a perennial and requires little maintenance. It appeals to people in both rural and urban areas because (unlike most trees) its leaves, fruits, seeds, and various other parts can be used in a multitude of ways. Moreover, it can grow quickly and easily and does not necessarily displace other crops.
Neem and the United States
In 1975 the U.S. Department of Agriculture research facility at Beltsville, Maryland, and 19 of its stations across the country embarked on a comprehensive program to study the pest-control properties of various plants. Several universities collaborated on this program; others worked independently. The research, which still continues at several locations, has demonstrated or verified the outstanding effects of neem extracts against numerous species of destructive insects and fungi. Of thousands of plant extracts tested, neem was by far the best.
In trials, crude alcohol extracts of neem seeds proved effective at very low concentrations against 60 species of insects, 45 of which are extremely damaging to American crops and stored products—causing billions of dollars of losses to the nation each year. They included sweet-potato whitefly (see page 94), serpentine leafminers (which attack vegetable and flower crops), gypsy moth (which causes millions of dollars of losses to homeowners and the forest industry), and several species of cockroach.
In 1985, the Environmental Protection Agency approved a commercial neem-based insecticide for certain nonfood uses. Called Margosan-O ®, the product is available at present in limited quantities in 21 states, and the amount is growing quickly. It is registered for use against such pests as whiteflies on chrysanthemums, leafminers on birch trees, aphids on roses, chinch bugs on lawns, gypsy moths on shade trees, and thrips on gladiolus. So far, it is being used primarily in professional greenhouses.
As a result of all this work, neem is seen as the nation's leading candidate for providing a new generation of broad-spectrum pesticides. However, neem cannot yet be legally used against pests that occur on food crops. Despite neem's apparent lack of toxicity or environmental danger, getting the authorization to use it on food plants will take time and great expense, because federal agencies require exhaustive testing before approving any pesticide for this purpose.
Although neem is essentially unknown to the American public, some neem-based consumer products are appearing in shops across the nation. Imported neem soap and toothpaste, for example, are sold fairly widely in specialty stores.
Neem production and processing also provides employment and generates income in rural communities—perhaps a small, but nonetheless valuable, benefit in these days of mass flight to the cities in a desperate search for jobs. It could be a useful export as well; a ton of neem seed already sells at African ports (Dakar, for example) at more than twice the price of peanuts. On top of all that, neem by-products (the seedcake and leaves, in particular) actually may improve the local soils and help foster sustainable crop production.
Although neem's ability to promote health and its value as a safe pest control is still only in the realm of possibility, there is no doubt that neem trees can provide the poor and the landless with oil, feed, fertilizer, wood, and other essential resources. In its crude state the oil from the seeds can have a strong garlic odor, but even in that form it can be used for heating, lighting, or crude lubricating jobs. Refined, it loses its unpleasant smell and is used in soaps, cosmetics, disinfectants, and other industrial products.
Neem cake, a solid material left after the oil is pressed from the seeds, is also useful. Broadcast over farm fields, it provides organic matter as well as some fertility to the soil. More important, it controls several types of soil pests. It is, for example, notably effective against nematodes, those virulent microscopic worms that suck the life out of many crops. Cardamom farmers in southern India claim that neem cake is as effective as the best nematode-suppressing commercial products.
Because neem is a tree, its large-scale production promises to help alleviate several global environmental problems: deforestation, desertification, soil erosion, and perhaps even (if planted on a truly vast scale) global warming. Its extensive, deep roots seem to be remarkably effective at extracting nutrients from poor soils. These nutrients enter the topsoil as the leaves and twigs fall and decay. Thus, neem can help return to productive use some worn-out lands that are currently unsuited to crops. It is so good for this purpose that a 1968 United Nations report called a neem plantation in northern Nigeria ''the greatest boon of the century" to the local inhabitants.
At a more basic level, the increasing scientific scrutiny of neem is providing biological insight into the way plants protect themselves against the multitude of plant eaters. It is a window on a battle in the continuing chemical warfare between plants and predators. And because it is part of this natural antagonism, neem is a promising candidate for use in the increasingly popular concept of integrated pest management. To employ neem in pest control is to take advantage of the plant kingdom's 400 million years of experience at trying to frustrate the animal kingdom.
For all its apparent promise, however, the research on neem and the development of its products are not receiving the massive support
Among many new developments in the 20 months since the first printing of this book, our attention has been caught by the following.