Although the possibilities seem almost endless, nothing about neem is yet definite. The scientists who are most enthusiastic over the plant and its potential admit that at this stage the evidence to support their expectations is tentative. Even within the world of pest control its eventual place is by no means clear.
The truth is that despite all its properties and promise, some impediments must be overcome and many uncertainties clarified before neem's potential can be fully realized. These obstacles are summarized in this chapter; more detail can be found in later chapters.
By and large, the limitations known today all seem surmountable. Indeed, they present exciting challenges to the scientific and economic-development communities. Solving them may well bring a major new resource and a means for benefiting much of the world.
Lack of Experience
The greatest impediment to neem's commercial development may simply be a general lack of credibility, or even awareness, of what it is and what it can do. Neither the public, the majority of pesticide manufacturers, nor the health-care community in industrial countries now appreciate the plant or its promise. This is due in part to a lack of experience, in part to a lack of industrial interest (caused notably by the difficulty of patenting natural products), and in part to a lack of laboratory data to substantiate the claims. One researcher has called the neem scene an "uncharted jungle" of miscellaneous assertions, disconnected details, and limitless possibilities.
Another difficulty is caused by the fact that many of the neem trees scattered around the world are (for all intents and purposes) genetically distinct. This means that conclusions drawn from one may not be exactly applicable to the others. Extracts from neighboring trees, for instance, may differ in their mixtures of ingredients.
There is no current evidence that this has caused any practical problems. Eventually, however, certain elite types will undoubtedly be selected and propagated.
Lack of Registration
In an era when many people are desperately seeking alternatives to synthetic pesticides, it is ironic that neem's very uniqueness is slowing its acceptance by regulatory authorities. Neem components incapacitate pests by repelling them, stopping them from feeding, or upsetting their growth—only indirectly by killing them. Its varying modes of action, its complex and synergistic mixture of ingredients, and its lack of standardization all raise barriers that trouble pesticide regulators.
Lack of Standards
Writing regulations to cover neem has been made even more difficult because no standard of potency has yet been developed. For consistency of composition, a mixed product from nature cannot compete with a single molecule from a laboratory. For instance, the mix of active ingredients may vary with the sample's age, the locality where it was grown, the genes of the tree it came from, or the method by which the sample was handled or shipped. Moreover, the analytical techniques are tricky and, for the moment at least, the various reports of neem's level of efficacy cannot all be trusted.
Although the tree is easy to grow, the specific horticultural and climatic conditions that maximize its potency are still unknown. Extracts from trees grown in different parts of the world currently show differing levels of activity, and the relative differences vary with the types of insects being tested. Sorting out just how genetics and environment—not to mention handling methods and insect species—influence neem's various ingredients is a knotty problem. Experience may eventually prove, for example, that the best-looking seeds from the fastest-growing trees on the most advantageous sites produce the poorest pesticides.
It is one of neem's strengths that its ingredients can be used in formulations from the crudest to the most sophisticated. On the one hand, in a remote Third World village farmers may take a sack of crushed neem kernels, dunk it (like a tea bag) in a barrel of water overnight, and use the resulting "neem tea" on their vegetable crops the next day. On the other hand, the isolation of individual neem ingredients is already being conducted in sophisticated factory settings in the United States. This produces highly purified and certifiably uniform products that are a world away from neem tea in a tub in Thailand.
Both approaches are valid, of course, but their needs, priorities, costs, and objectives are so vastly different that people working at the two extremes may appear (even to themselves) to be working at cross-purposes. To the uninitiated, the conflicting views can make the whole neem concept seem unreliable.
The commercial production of any materials derived from the fruit of a tree is necessarily constrained by nature. There are limitations of seasonal supply, the long wait for the trees to mature, and the difficulty of facing the whims of nature. (For instance, in India neem fruits drop during the late monsoon, a time when frequent rains make them hard to dry.)
On the other hand, in many tropical nations neem pesticides should prove to be much cheaper than synthetic pesticides, and they could be homegrown rather than imported. However, they will never be totally without cost. Gathering and processing neem products takes time and effort. Even people "growing their own" will probably have to take time off from farming, fuel gathering, or other vital activities to harvest their neem seed. Moreover, if pests arrive during a season when fresh seeds are unavailable, facilities for storing the seeds for future use will be needed.
Contributing notably to the expense (at least in new plantings) is the delay of several years before the first crop can be gathered. Not only must the growers carefully nurture the young tree during its first year or so, they will begin getting returns only after its fifth year under normal conditions.1
There can be other economic uncertainties as well. As we have noted, for instance, it is not yet known how best to manage the tree to optimize its production of pesticidal ingredients. Nor is it yet known if and how the mix or quality of the pest-control compounds will change in any economically meaningful way with the location, the climate, or the tree's age.
Although neem products (seeds, extracts, or seedcake) are safe and easy to handle and apply, they are bulky and some samples smell like a dreadful cross between garlic and peanut butter.
There is at this point no method for mechanizing the process of collecting, storing, or handling the seeds. Nor is it yet known how to carry out these operations so that the pesticidal ingredients retain their fullest potency.
Neem trees cannot be grown just anywhere. They are sensitive to frost and can be produced only in the warmer parts of the world. There is also mounting evidence that under dry conditions their growth and yield can be erratic and their susceptibility to pests high.
The seed's short viability is a problem in introducing neem to new locations. Fresh seeds germinate well, but within weeks germination rates begin dropping off. This poses logistical difficulties for any tree-planting endeavors outside the areas where the tree now grows.
At this stage at least, neem seems primarily suited for individual or group plantings within household compounds and villages, along roadsides and canals, in marketplaces and parks, and around the edges of fields. However, its production in organized commercial plantations in the long term might prove to be its greatest value.
Usually there is little difficulty with livestock eating the seedlings or saplings, but humans filching the foliage for medicinals or toothbrushes can be a problem.
When exposed to sunlight, neem products degrade and lose their pest-control properties. Typically, the crude extracts remain active for only eight days when exposed to the sun's ultraviolet rays.
Under sophisticated conditions this limitation can be overcome. The neem formulation being sold in the United States, for instance, contains sunscreens. When sprayed on plants, it remains effective for 2-3 weeks, and it can be stored for at least 2 years with little or no loss of potency.
Neem materials are also sensitive to high temperatures and must be stored in shady places.
These inherent instabilities can be exacerbated when the extracts are made under uncontrolled conditions, such as in a Third World village. For example, the active compounds may be inactivated by acids, alkalis, or other contaminants of local water supplies. Other types of pesticides might well be similarly affected, but neem extracts are more likely to be prepared where water is impure.
Although neem has shown every indication of being safe to mammals in normal use as a pesticide (see Appendix A), the possibility of future hazards should not be dismissed. Few toxicity tests on higher mammals such as dogs, pigs, primates, or people have yet been published. As a result, in the United States neem products are not yet authorized for use on food crops. Their persistence in residues on foods is also unknown.
A known health hazard may arise as a result of poor handling. The harvested fruits must be depulped quickly and the seeds dried under shade and stored under shelter from the sun and rain. This is because at moisture contents above 14 percent, the fruits can carry the fungus Aspergillus flavus, which under many conditions produces aflatoxins. These are among the most potent carcinogens known and, unfortunately, they can contaminate the seeds inside the fruits. Indeed, they are extracted and concentrated along with the pesticidal ingredients. This may eventually prove to be the greatest barrier to the wider use of the pesticides from this most promising tree. It is, however, a problem only in the more humid neem-growing areas. Elsewhere, the climate is usually too dry for fungi to infect the fruits.
The fact that neem extracts are natural products does not mean that they are benign. Indeed, there is evidence that they can affect certain aquatic life. Most studies with fish in laboratory tests have shown no deleterious effects, but in one trial both tadpoles and the mosquito-eating fish gambusia died when neem extracts were applied to the water.2 And neem seeds falling into fish ponds in Haiti killed tilapia
fry.3 These experiences do not necessarily indicate an environmental hazard—only that caution and more toxicological studies are needed. It seems likely that neem oil, rather than the other seed-kernel ingredients, is causing the toxicity.
Although using neem will seldom harm beneficial insects, there are a few cases of negative effects. There is, for instance, a report of it affecting the larvae of hover flies. Also, there may be other subtle secondary effects. Bees and butterflies drinking nectar from neem-dosed plants might, for example, pick up traces of neem components, leading to reduced reproduction. The same may be said for insects that feed on other insects. To date, however, no evidence for such deleterious effects has surfaced.
Compared to DDT and other synthetic pesticides, the wait for neem to act may seem endless. Insects treated with it die by delayed action. Although their destructive power drops fast as the neem materials take effect, they may continue living for 2 weeks. Eventually, however, the next generation fails to emerge and the population collapses.
Although the end result may be more devastating than that from DDT, people used to seeing rapid knockdown may be initially disappointed, or even discouraged. This lack of quick effect poses a challenge for promoting neem in pest-control markets where people have come to expect instantaneous results.
Damage to Plants
It is one of neem's most exciting features that its compounds are systemic. However, they are not systemic in all plant species. Potato plants, for example, do not take up the main active ingredient, azadirachtin, whereas beans do. This introduces yet another uncertainty. Each plant species may have to be checked individually. Also, the acidity of the soil or the level of enzymatic activity in the plant may affect the length of time that neem compounds remain effective inside the plant tissues.
Moreover, it has been found in greenhouse and field trials that certain neem materials can damage plants. In cabbages, for example, only medium-sized heads were formed. In onions, the waxy coating on the leaves was destroyed. In tomatoes, the growth and yield were reduced.
Much of this "phytotoxicity" was apparently due to neem oil contaminating the samples. There were large differences between the
Method of Application
Although neem products can be applied using standard equipment (both sophisticated and primitive), they may have specific requirements if they are to be fully effective. For example, some pests must be treated at a certain time of day. Colorado potato beetle is one. If potato fields are sprayed when the sun is high, the extracts dry out and have little effect. On the other hand, if sprayed at dawn, they can be extremely effective.
A product like this, which affects certain subtle aspects of an insect's life, is restricted by factors having to do with the insect's habits, life stage, and metabolic processes. In many cases the users will have to be educated, or at least trained, before neem can be fully effective.
Protecting the Tree
Despite the fact that it is a source of pesticidal materials, the tree itself is attacked by certain pests. In 1986, for example, an outbreak of the oriental yellow scale was confirmed in West Africa (see next chapter). This insect, a native of India and the Far East, defoliates and sometimes kills the tree. Recent reports suggest that it has severely damaged neem trees over large areas of northern Cameroon, Chad, northeastern Nigeria, and eastern Niger. It seems likely that this outbreak resulted from the stresses of a decade or more of drought in the Sahel, which has left many neems weak and sickly.4 Nonetheless, further devastating pest outbreaks are certainly possible.
Whereas millions of Indians swear to the efficacy of neem treatments, the pharmacological effects have seldom been subjected to rigorous trials with controls. Thus, to officials in many other parts of the world, today's claims of medical efficacy are suspect. Indeed, a couple of recent studies suggest that it may be unsafe to eat neem products.
One study (already mentioned) dealt with the use of neem oil as a general cure-all for children. It strongly suggests that this is a most unwise practice, at least among the very young. When children under
There are also anecdotal accounts from West Africa of neem-leaf teas possibly causing kidney damage when taken over a long period.
The ultimate significance of these preliminary studies is unclear. The materials used may well have been contaminated—perhaps by fungal toxins. Other trials have found no toxicity problem. For instance, in a toxicological study in Germany, neem oil obtained from clean, fungus-free seed kernels showed no oral toxicity in rats. The dosage tested was 5,000 mg per kg body weight.8
Certainly, no hazard has been observed when neem has been used in topical treatments (on skin complaints, for example) or in dental uses—which together make up by far the major medical applications. Nor is there any evidence that using the seed-kernel extracts as pesticides is hazardous to health.
Whether neem oil is safe for possible use as an intravaginal spermicide is also unclear. However, in this use there are perhaps even greater uncertainties. Contraception is a topic of such sensitivity—personal, political, scientific, and religious—that here, too, its future role is uncertain.
Its use as a spermatocide—the male contraceptive mentioned earlier—is so uncertain that it will likely take decades of research to develop even if no safety hazards are found along the way.
The number and complexity of the compounds in neem extracts will always preclude the economic synthesis of the full mixture. On the other hand, individual compounds may prove suitable for synthesis. There is, therefore, the possibility that if neem opens up a new generation of pesticides, synthetic mimics may capture some of the more lucrative "top-end" markets.