Potential of the Neem Tree (Azadirachta indica) for Pest Control and Rural Development I

SALEEM AHMED 2 AND MICHAEL GRAINGE 3

The neem tree (Azadirachta indica) contains promising pest-control substances found effective against many economically important pests. These materials are easy to process by village-level industries and easy to use by limited-resource farmers, thereby offering potential for crop protection and off-farm income generation. The tree's numerous pharmacological and other complementary uses make it doubly attractive for incorporation in large-scale rural development efforts.

With limited scope for land expansion coupled with steady population increase, the land : labor ratio in many developing countries is becoming increasingly less favorable. The unequal distribution of ownership of productive assets, work op- portunities, and income within the rural sector is widening disparities between the "haves" and the "have-nots" and squeezing limited-resource farmers and the landless poor. In many developing countries, this is causing substantial rural- urban population migration. However, the inadequacy of work opportunities in many urban areas is confounding the problem and leading to greater urban pov- erty, adversely affecting quality of life in the process.

Rural development strategies usually strive to reverse this trend in population migration. However, efforts to increase attractiveness of farming are often frus- trated by many problems; pest damage ranks among the more serious ones. More than 20,000 species of field and storage pests annually destroy approximately one- third of the world's food production (McEwen, 1978), valued at more than $100 billion. Highest losses occur in developing Asian and African countries, and rice and maize crops--the staple food in many developing countries--are among those hard hit (Table 1). These losses are either compensated by food imports, which drain the limited foreign exchange reserves of poorer countries, or are reflected in higher food prices and supply uncertainties, which can lead to malnutrition and famine.

To alleviate pest problems, synthetic pesticides are often used. These, however, may have drawbacks--including toxicity to nontarget organisms, development of pest resistance, and environmental degradation. In developing countries, inade- quate product knowledge, supply uncertainties, and high prices cause inefficient pesticide use (Herdt, 1979) and also create additional socioeconomic problems between the "haves" and the "have-nots." Alternative pest control strategies, especially those that are effective and low-cost, are thus needed. Crude plant extracts may play an important role here (Brady, 1982).

Received 14 November 1984; accepted 10 October 1985. 2 Research Associate, Resource Systems Institute, East-West Center, 1777 East-West Road, Ho-

nolulu, HI 96848. Graduate student in plant pathology, University of Hawaii, on East-West Center scholarship.

Economic Botany, 40(2), 1986, pp. 201-209 �9 1986, by the New York Botanical Garden, Bronx, NY 10458

202 ECONOMIC BOTANY [VOL. 40

TABLE 1. ESTIMATED CROP AND REGIONAL LOSSES DUE TO AGRICULTURAL PESTS. a

% of potential production

Crop losses Regional losses

Rice 46 Asia 43 Maize 35 Africa 42 Whea t 24 South Amer ica 33 Sorghum and Nor th Central

mil let 38 Amer ica 28 Sugarcane 55 Europe 25

�9 Source: McEwen, 1978.

PLANTS WITH PEST-CONTROL POTENTIAL

The earliest mention of poisonous plants is found in the Rig Veda, the classic book of Hinduism, composed in India during the second millennium B.C. (Chopra et al., 1949). The ancient Romans used false hellebore (or white hellebore, Ver- atrum album or 1I. viride) as a rodenticide, and the Chinese are credited with discovering the insecticidal properties of Derris species (Feinstein, 1952). In A.D. 970, the Arab scholar Abu Mansur listed 584 natural materials--mostly plants-- possessing pharmacological and poisonous properties (Achundow, 1889). Pyre- thrum was used as an insecticide in Persia and Dalmatia (Nelson, 1975), and tobacco plant preparations have been similarly used for nearly 2 centuries (Frear, 1943). More recently, a listing of approximately 700 plant species reportedly used in different parts of the world for pest control--regardless of actual efficacy--has been compiled (Secoy and Smith, 1983). A few species are used even currently for pest control in some cultures. For stored-grain pest control, for example, Indo- Pakistani farmers use neem leaves (Ahmed and Koppel, 1985), while various Nigerian tribes use roots, stems, and leaves of a dozen species of plants (Giles, 1964). From published reviews (Mclndoo, 1945; Heal et al., 1950; Jacobson, 1958, 1975) and survey responses, we have listed some 1,600 plant species re- portedly possessing pest-control properties (Grainge et al., 1985). Recent infor- mation has come primarily from developing countries, indicating a resurgence of interest there in the subject.

For effective propagation and utilization by limited-resource farmers, plant species for pest control and rural development should ideally possess the following characteristics:

(iv) (v)

Crude

(i) be perennial; (ii) require little space, labor, water, and fertilizer;

(iii) not be destroyed each time the pest-control material is obtained from them; not become a weed or host to pests; and possess complementary uses.

extracts from such species should:

(i) effectively control target pests with minimum disruption of nontarget organisms;

(ii) be easy to process/formulate with village-level technology;

1986] AHMED & GRAINGE: NEEM 203

(iii) be easy to use with skills and resources available with limited-resource farmers; and

(iv) be environmentally safe.

Few species may possess all these characteristics. We have identified 25 that come close (Ahmed et al., 1984). The neem tree (Azadirachta indica) appears particularly promising. Its growth habit and various uses are described below.

NEEM TREE: PROMISING FOR PEST CONTROL AND RURAL DEVELOPMENT. 9

Azadirachta indica A. Juss.; syn. Melia azadirachta L. and Melia indica (A. Juss.) Brand. Neem tree or margosa tree. (Also known as neeb in Arabic, neem in Hindi and Urdu, azad dirakht in Persian, and nimba in Sanskrit.) Meliaceae.

This is a hardy, fast-growing evergreen tree with straight trunk, moderately thick bark, and round crown. Mature trees attain heights of 7-20 m with a spread of 5-10 m (Ketkar, 1976). They produce fruits the size of shelled peanuts in 4-5 yr, become fully productive in 10, and may live for more than 200 yr. Mature trees produce 30-50 kg of fruit annually, which fall to the ground on ripening (Ketkar, 1976).

Distribution

In its native Indo-Pakistan subcontinent, neem is found in a large belt extending southwards from Delhi and Lahore to Cape Comorin. In South Asia, it is also found in Bangladesh, upper Burma, and in the drier parts of Sri Lanka. In South- east Asia it occurs scattered in Thailand, southern Malaysia, and in the drier Indonesian islands east of Java. It is also found in the northern plains of Yemen and has been recently introduced into Saudi Arabia. In Africa, it is particularly widespread in Nigeria and Sudan; it is also found along the East African coastal plains stretching from Ethiopia across Somalia, Kenya, and Tanzania to Mozam- bique and in the West African sub-Sahelian region of Mauritania, Togo, Ivory Coast, and Cameroon (Heinz Schmutterer, University of Giessen, pers. comm., 1984). In the New World it is found in Haiti (Lewis and Elvin-Lewis, 1983) and Suriname and is a recent introduction in Cuba and Nicaragua. Neem plantings are being currently introduced on 40,000 ha of forest land in the Philippines (A.S. Balyut, Philippine Bureau of Plant Industry, pers. comm., 1983). According to a 1959 survey, India has approximately 14 million neem trees (Ketkar, 1976).

Ninteenth-century immigrants also carried the tree from its native Indo-Pa- kistan region to Fiji and Mauritius; now it is an integral part of the native flora there and has also spread to other islands in the South Pacific.

Management needs

Neem thrives under subhumid to semiarid conditions and can be established without irrigation in warm areas with rainfall of less than 500 mm/yr (Ketkar, 1976; Radwanski and Wickens, 1981). It is grown from ripe seed, seedling, or sapling. However, seeds lose viability after 2 wk; thus, a ton of Burmese neem seed failed to germinate in the Philippines (Jesus Sumungil, Philippine Bureau of Plant Industries, pers. comm., 1982). Depulped mature seeds last longer under cool, dry conditions (Radwanski and Wickens, 1981). Once planted, neem requires virtually no further attention, fertilizer, or supplemental irrigation. The tree's

204 ECONOMIC BOTANY [VOL. 40

growth habits, management needs, and uses have been reviewed by Radwanski (1977) and Ketkar (1976). Melia azedarach L. (chinaberry), a closely related species, is also found in more humid tropical areas such as Hawaii and South China.

Pest control use and action modes

Traditionally, for stored-grain pest control, Indo-Pakistani farmers simply mix 2-5 kg of dried neem leaves/100 kg grain (Ahmed and Koppel, 1985); or they soak empty sacks overnight in water containing 2-10 kg of neem leaves/100 liter water and then dry these sacks before filling them with grain (Ahmed, 1984). Some farmers also mix ground neem-leafpaste with mud used for making earthen containers for grain storage. Such practices, however, are gradually dying--due in part to the stigma of "backwardness" associated with the use of traditional materials and practices in agriculture (Ahmed, 1984).

H. H. Mann and W. Burns reported as early as 1927 that neem leaves were not attacked during the 1926-27 locust invasion of western India (Jotwani and Sri- vastava, 1981). Similar observations were recorded in 1962 when locust swarms invaded Delhi. Standing crops at the Indian Agricultural Research Institute Ex- periment Station were sprayed with a 0.1% neem-kernel suspension at the rate of 300-600 liter/ha depending upon the crop and growth stage. No feeding was observed, although locusts settled on treated crops. In contrast, adjacent untreated crops were destroyed (Jotwani, 1983).

A pool of biologically active constituents, including the triterpenoids azadi- rachtin, salanin, and meliantriol, are found in neem leaf, fruit, bark, and seed (Schmutterer, 1982; Warthen, 1979; Ketkar, 1976). These compounds reportedly control more than 100 species of insects, mites, and nematodes--including such economically important pests as the desert and migratory locusts, rice and maize borers, pulse beetle and rice weevil, rootknot and reniform nematodes, and citrus red mite (Grainge et al., 1985; Warthen, 1979; Jacobson, 1958, 1975). Modes of control include antifeedant, growth regulatory, repellent, hormonal, or pesticidal action in larval and/or adult stages of these pests.

Potential for neem-based cottage industry

Neem leaves (Ahmed and Koppel, 1985), water extract of crushed neem seed (Jotwani and Srivastava, 1981), neem oil (Saxena et al., 1984a), and neem "cake" (Saxena et al., 1984b) appear particularly promising for pest-control use by de- veloping country, limited-resource farmers. Neem oil, possessing garlic-like odor, is produced by crushing depulped neem seed; the residue after extraction is the cake. The latter product, which looks like soil, is spread over the field by hand and worked into the soil. Application of crushed neem-seed water extract and neem oil, however, may require the use of a sprayer, which may not be available with many limited-resource farmers.

A simple animal-drawn oil crusher (ghanee) or an electrically operated oil expeller may be used for obtaining neem oil and cake. Both types exist in India's rural areas (Ketkar and Ketkar, 1984). The electrically operated expellers cost between US$5,000 and $30,000 and have crushing capacities of 5-10 tons of depulped neem seed per day (Ahmed, 1984). Machinery needed (expeller, boiler, filter press, shaft pulley, decorticator, and neem cutter) is locally fabricated, and

1986] AHMED & GRAINGE: NEEM 205

plant operation is relatively simple. Neem-seed crushing is a seasonal operation, extending in India for about 100 days during summer/fall.

Farmers are paid approximately $0.10/kg for depulped and dried seed; $0.08/ kg for depulped and undried seed; and $0.04/kg for undepulped fruit they bring to the plant. Farmers "sweep" neem fruit from their backyards and from other trees growing wild or along roadsides. Children help in the generation of this supplemental family income. For depulping, neem fruit is soaked for 2-5 days in water and then trampled upon or rubbed vigorously to separate the skin, which is used as a manure. The depulped seed is then dried. In this form it can be stored for up to a year without losing pest-control effectiveness. Dried neem fruit contains approximately 10% oil and 12% cake (Ketkar and Ketkar, 1984). Neem oil cur- rently sells in India for $1.20-1.30/kg, and neem cake for $0.10/kg ex factory (Ahmed, 1984).

Approximately 60-150 kg neem leaves would be needed to protect 2-3 MT of grain in storage, and about 50-200 kg neem cake to protect 1 ha of paddy in the field. Thus, 2-3 neem trees may be sufficient to provide adequate material to protect 1 ha of a crop in the field and its harvest in storage.

NEEM'S COMPLEMENTARY USES

Neem's various plant parts reportedly have anthelmintic, antiperiodic, anti- septic, antisyphilitic, astringent, demulcent, diuretic, emmenagogic, emollient, and purgative actions and have also been used to treat boils, eye diseases, exzema, headaches, hepatitis, leprosy, rheumatism, scrofula, and ulcers (Achundow, 1889; Ketkar, 1976; Chopra et al., 1956; Baquar and Tasnif, 1967). Indo-Pakistani villagers bathe in neem water as a preventive against heat rash and boils (Ahmed, 1984). Neem twigs are commonly used in south Asia to clean teeth, and neem toothpaste and toothpowder are also available. Neem is an excellent shade tree, and the air under it is considered good for health by Indo-Pakistani villagers.

In many Indian communities, neem traditionally occupies an important place in socio-cultural-religious events. In early March, in the Gudhi Padwa festival, which falls on the first day of Chaitra (the first day of the Hindu calendar), neem leaves are eaten first thing in the morning after cleaning one's teeth and worship- ping the sun (Ahmed, 1984). This is to purify blood. Water in which neem leaves have been soaked overnight is also drunk first thing in the morning on a routine basis by some people as a preventive against numerous ailments.

Neem oil contains over 35% saturated fats and virtually no polyunsaturated acids, making it suitable for soap manufacture. Approximately 60% of neem oil collected in India is utilized for this purpose (Ketkar and Ketkar, 1984). Neem cake is used in livestock feed and for fertilizer-coating because of its nitrification- inhibiting properties (Ketkar, 1976). The high carbohydrate and mineral content in neem pulp makes it useful for methane gas generation (Radwanski and Wickens, 1981). Young neem leaves are edible. The tree's hard, termite-resistant wood is used in construction; its resin is a gum substitute (Ketkar, 1976). Neem oil is now being tested for use in cosmetics, such as nail polish (H. Schmutterer, Univ. Giessen, pers. comm., 1984).

Neem's extensive roots can extract nutrients from deep subsoils and enrich surface soils through litter. Thus, in northwest Nigeria, significantly higher total

206 ECONOMIC BOTANY [VOL. 40

cations, cation-exchange capacity, base saturation, and pH were observed in soils under neem than in similar soils under fallow (Radwanski and Wickens, 1981). Phosphorous, however, was lower under neem, indicating its storage probably in plant parts other than leaves and twigs. Neem is salt-tolerant and can be grown on marginal soils with low fertility. Its introduction into the Sokoto Province of northwest Nigeria in the early 1930s, for example, is heralded as the "greatest boon of the century" because of the plant's ability to provide much-needed fuel and timber in the vast rain-deficient Sahel region (Radwanski and Wickens, 1981).

Small wonder, then, that the tree is called Azadirachta, the name derived from azad dirakht, which in Farsi, Urdu, and Hindustani (the national languages of Iran and Pakistan, and the lingua franca of India, respectively) means "free tree." In our literature review, Abu Mansur provides the earliest reference to this name (Achundow, 1889).

TOXICOLOGICAL AND OTHER LIMITATIONS

Neem extracts have generally been found safe--even beneficial--for mammals and the environment. For example, incorporation of 20% neem cake in diet resulted in higher growth rate in sheep (Vijjan et al., 1982); rats fed with Neemrich- 100 (tech) at doses up to 600 mg/kg body weight exhibited greater weight gain and no overt toxicity (Qadri et al., 1984); aqueous neem extracts lowered blood pressure and increased respiration rate in dogs (Arigabu and Don-Pedro, 1971); and no toxicity was observed in albino rats and mice fed with nimbidin at doses up to 2,000 mg/kg orally and 1,000 mg/kg intraperitoneally; on the other hand, nimbidin demonstrated significant anti-ulcer potential (Pillai and Santhakumari, 1984a,b).

Neem extracts have little effect on predators and parasites of rice insect pests (Saxena, 1983), and human subjects showed no side effect of importance after oral and intravenous administration of 7,000 and 1,000 mg, respectively, of sodium nimbinate (Jotwani and Srivastava, 1981). Undiluted neem oil showed strong spermicidal action and was 100% effective in preventing pregnancy in rhesus monkeys and human subjects when applied intervaginally before sexual intercourse (Sinha et al., 1984). Earlier, Sharma and Saksena (1959) investigated spermicidal action of sodium nimbidinate.

However, some neem extracts have been found toxic to guinea pigs and rabbits (Satire et al., 1984), and the insectivorous fish Gambusia spp. and tadpoles died at 0.04% concentration of neem extracts (Jotwani and Srivastava, 1981). Also, 5-30 ml of neem oil, when given to infants for treatment of minor ailments, caused vomiting, loose motions, seizure, loss of consciousness, and coma (Sinniah and Baskaran, 1981). These conflicting findings indicate the need for systematic toxicological studies.

Poor soil drainage may retard neem growth. The tree is frost-tender, especially in seedling and sapling stages. There also have been reports of minor pest infes- tations (Radwanski and Wickens, 1981; Warthen, 1979).

Some operational problems in the collection and processing ofneem fruit have been reported. These include: (i) people have to cover large areas to collect sizeable quantities ofneem fruit as trees are generally found scattered; (ii) neem fruit ripens and falls during the April-July rainy period, when it is difficult to collect and

1986] AHMED & GRAINGE: NEEM 207

store; it also gives off an offensive odor; and (iii) fruit thus collected contains considerable moisture, which gives off much heat due to autooxidation, often charring the fruit and making it useless for oil production (Ketkar and Ketkar, 1984).

To overcome these problems, additional incentives for neem fruit collection may be needed; better methods for drying and storing the fruit also need to be considered.

CONCLUSION

Rural development aims at bringing about a certain level of well-being in the community. This is usually obtained through strategies that result in adequate agricultural production, gainful on- and off-farm employment, adequate avail- ability of health care and other services, and a certain level of resiliency in the community to "spring back" from adverse effects of any natural or man-made calamity that may strike the area from time to time. Since efforts to increase crop production are often frustrated by crop pests and since synthetic pesticides may be inappropriate under limited-resource farming conditions, we need alternative pest-control strategies that are socially and ecologically compatible with local needs and constraints; strategies that simultaneously provide for rural develop- ment are particularly sought.

The neem tree, we feel, potentially offers much promise in this connection.

LITERATURE CITED

Achundow, A. C. 1889 (1968) Die pharmakologischen Grunds~tze des Abu Mansur Muwaffak bin Ali Harawi. In Kobert's Historische Studien aus dem Pharmakologischen Institut der Univer- sit~t Dorpat. Halle 1889-96. Compiled in 1968 under Historische Studien zur Pharmakologie der Griechen, R/Smer und Araber, p. 138-284. Zentralantiquariat der Deutschen Demokra- tischen Republik, Leipzig.

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Giles, P. H. 1964. The storage of cereals by farmers in northern Nigeria. Trop. Agric. 41: 197-212. Grainge, M., S. Ahmed, W. C. Mitchell, and J. W. Hylin. 1985. Plant species reportedly possessing

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