Neem for Sustainable Pest Management and Environmental Conservation

This article is from ECHO Asia Note #24

[Editor’s Note: Dr. Ramesh C. Saxena is a world-renowned scientist and Neem expert and Chairman of the Neem Foundation in Bombay, India. This article is gratefully reprinted from a forthcoming book about the usefulness of the Neem tree entitled “Neem: Nature’s Healing Gift to Humanity,” compiled and edited by Klaus Ferlow of the Neem Research organization of Canada.]

Abstract

To be sustainable, agricultural processes, including pest and vector management must be efficient (effective and economically rewarding), ecologically sound (for long term stability), equitable (in providing social justice), and ethical (in respecting both future generations and other species). Basic and applied research conducted over the past three decades have shown that the use of natural and enriched neem (Azadirachta indica) products can provide a key component in ensuring sustainable integrated pest and vector management. The formidable array of more than 100 bioactive compounds in the neem tree makes it a unique plant with potential applications in pest and vector management. Unlike toxic synthetic insecticides, neem materials do not kill the pest, but incapacitate or neutralize it via cumulative behavioral, physiological, and cytological effects. In spite of high selectivity, neem materials affect more than 500 species of insect pests, phytophagous mites, mites, and ticks affecting man and animals, parasitic protozoans, noxious mollusks, plant parasitic nematodes, pathogenic fungi, and harmful bacteria and fungi. Results of large-scale field trials have illustrated the value of neem-based pest management for enhancing crop productivity. Neem is useful as windbreaks and in areas of low rainfall and high wind speed, it can protect crops from desiccation. Neem trees are being planted on a large scale in southern China and Brazil. Neem has also been grown in Australia, in many countries in Africa, Latin America, Caribbean islands, etc. Neem has much to offer in solving agricultural and public health problems, especially in rural areas. Increased awareness of the potential of neem tree by creating awareness of its potential would go a long way in promoting its acceptance for pest management and improvement of plant health, animal health, human health, and environmental health.

Introduction

The global population is now 7.3 billion. Providing adequate food entitlements, safeguarding public health, meeting fuel and firewood needs, and at the same time preventing deforestation, conserving the environment, and slowing down the population growth will be daunting challenges in the coming decades. Although “green revolution technologies” have more than doubled the yield potential of cereals, especially rice and wheat in India, these high -input production systems requiring large quantities of fertilizers, pesticides, irrigation, and machines disregard the ecological integrity of land, forests, and water resources, endanger the flora and fauna, and cannot be sustained over generations. Future food security and economic development will depend on improving the productivity of biophysical resources through the application of sustainable production methods, by improving tolerance of crops to adverse environmental conditions, and by reducing crop and post-harvest losses caused by pests and diseases. Appropriate technologies, which do not assault nature, will have key roles to play in ensuring food security, in improving public and animal health, and in rehabilitating the environment to safeguard the wellbeing of future generations. Instead of striving for more “green revolutions” with emphasis on miracle seeds, hard-hitting synthetic and engineered pesticides, and increased use of fertilizers, the future must look to natural ways and processes for augmenting agricultural productivity. In fact, all development efforts and activities, including pest management, should be within well-defined ecological rules rather than within narrow economic gains. Sustainable agricultural systems must be efficient (i.e. effective and economically rewarding) and ecologically sound for long-term food sufficiency, equitable in providing social justice, ethical in respecting both future generations and other species, and lead to employment and income-generating opportunities. For India and other countries, the use of neem may provide a key component in more sustainable agricultural systems, including pest and nutrient management, animal health, human health, and environmental conservation.

Why Neem?

Neem, a member of the Meliaceae family, is a botanical cousin of mahogany. According to a report of an ad hoc panel of the Board on Science and Technology for International Development, “this plant may usher in a new era in pest control, provide millions with inexpensive medicines, cut down the rate of human population growth and even reduce erosion, deforestation, and the excessive temperature of an overheated globe” (National Research Council 1992). Neem’s other descriptions, such as “nature’s bitter boon,” “nature’s gift to mankind,” “the tree for many an occasion,” “the tree that purifies,” “the wonder tree,” “the tree of the 21st century,” and “a tree for solving global problems,” are recognition of its versatility. Its botanic name, Azadirachta indica, derived from Farsi,”azad darakht-i-hindi” literally means the “free or noble tree of India,” suggesting that it is literally free from pest and disease problems and is benign to the environment. Neem’s Sanskritized name “Arishtha” means the reliever of sickness. In East African Kiswahili language, neem is known as “Mwarubaini,” meaning the reliever of 40 disorders.

Neem is native to Myanmar and the arid regions of the Indian sub-continent, where it has almost been semi-domesticated. During the last century, neem was introduced in arid zones of Africa. Today, it is grown in many Asian countries, in tropical regions of the New World, in several Caribbean and in some Mediterranean countries. During the past three decades, neem was introduced and planted on a large scale in Australia, in the Philippines, and also in the Plains of Arafat near Meccah in Saudi Arabia, regions ecologically highly diverse. Over the past decade, more than 25 million neem trees have been grown in southern China, particularly in Yunnan province. In all these regions, the tree is thriving - a testimony to its hardiness and adaptability. Neem, however, is unsuited to growing in cooler and mountainous areas (>1000 m).

Neem is an evergreen, tall, fast-growing tree, which can reach a height of 25m and 2.5m in girth. It has an attractive crown of deep-green foliage (which can spread 10 m across) and masses of honey-scented flowers. The tree thrives even on nutrient-poor dry soil. It tolerates high to very high temperatures, low rainfall, long spells of drought, and salinity. It is propagated by seed; 9 to 12 month-old seedlings transplant well. Birds and bats also disperse the seed. Fruiting begins in 3 to 5 years. In the Indian sub-continent, neem flowers from Jan through Apr and fruits mature from May to Aug. In coastal Kenya, fruiting occurs in March and April; some off types also fruit in Nov or Dec. The fruit is about 2 cm long, and when ripe, has a yellow fleshy pericarp, a white hard shell, and a brown, oil-rich seed kernel. Fruit yields range from 30 to 100 kg per tree, depending on rainfall, insolation, soil type, and neem ecotype or genotype. Fifty kg of fresh fruit yields 30 kg of seed, which gives 6 kg of oil and 24 kg of seed cake. Seed viability ranges from 6 to 8 weeks, but thoroughly cleaned and properly dried and cooled seeds remain viable up to 6 months. Propagation by stumps and stem cuttings also is practiced. Plantlets, produced by tissue culturing, have also been used for propagation with partial success.

Neem is bitter in taste. The bitterness is due to the presence of an array of complex compounds called “triterpenes” or more specifically, “limonoids.” More than 100 unique bioactive compounds have been isolated from various parts of the neem tree; still more are being isolated. This formidable array of highly bio-active compounds makes neem a unique plant with potential applications in agriculture, animal care, public health, and for even regulating even human fertility. The limonoids in neem belong to nine basic structure groups: azadirone (from oil), amoorastatin (from fresh leaves), vepinin (from seed oil), vilasinin (from green leaves), gedunin (from seed oil and bark), nimbin (from leaves and seed), nimbolin (from kernel), and salannin (from leaves and seed), and the aza group (from neem seed). Azadirachtin and its analogs have fascinated researchers for the past 40 years because of phagorepellency, growth inhibition, and chemosterilizing effects on insect pests (Saxena 1989, Schmutterer 1990, 2002). The azadirachtin content in neem could vary considerably due to edaphic, climatic, or genotypic differences.

Neem for Eco-friendly Sustainable Pest Management

Crop Pests

Pest control as practiced today in most developing countries relies mainly on the use of imported pesticides. This dependence has to be reduced. Although pesticides are generally profitable on direct crop return bases, their use often leads to the contamination of terrestrial and aquatic environments, damage to beneficial insects and wild biota, accidental poisoning of humans and livestock, and the twin problem of pest resistance and resurgence. More than 500 arthropod pest species have become resistant to one or more insecticides. Resistance of the cotton boll worm in India and Pakistan, of the Colorado potato beetle in the USA to all available insecticides, and of the diamondback moth to all classes of insecticides, including Bacillus thuringiensis (Bt), in Hawaii, Malaysia, the Philippines, Taiwan, and Thailand, illustrate the complexity of the problem. Shifts in pest status – from minor to major, and resurgence of pests, such as whiteflies caused by direct or indirect destruction of pests’ natural enemies are other unwelcome developments associated with pesticide use. A World Health Organization and United Nations Environment Program report estimated that there are 1 million human pesticide poisonings each year in the world, with about 20,000 deaths, mostly in developing countries. The problem is rendered even more difficult because few, if any, new compounds are coming to replace old insecticides. The cost of developing and registering new pesticides is staggering: almost US $60 million, and pesticide manufacturers are unwilling to risk investment on products whose market life could be shortened by development of pest resistance.

For ecologically sound, equitable, and ethical pest management, there is need for control agents that are pest specific, nontoxic to humans and other biota, biodegradable, less prone to pest resistance and resurgence, and relatively less expensive. Among various options, neem has been identified as a source of environmentally “soft” natural pesticides.

Neem has had a long history of use primarily against household and storage pests and to some extent against crop pests in the Indian sub-continent. As early as 1930, neem cake was applied to rice and sugarcane fields against stem borers and white ants. Early observations that swarming locusts did not attack neem leaves have been confirmed in laboratory studies and attributed to neem’s antifeedant activity against locusts.

The pest control potential of neem in developing countries, however, remained largely untapped due to the advent of broad-spectrum synthetic insecticides. Also, publicity given to slogans such as “the only good bug is a dead bug,” and identifying traditional uses of neem as backward, gradually weaned people away from using neem. It is only in the past two decades that the pest control potential of neem has been appreciated. Though subtle, neem’s effects such as repellence, feeding and oviposition deterrence, growth inhibition, mating disruption, chemo-sterilization, etc. are now considered far more desirable than a quick knock-down in integrated pest management programs as they reduce the risk of exposing pests’ natural enemies to poisoned food or starvation. In spite of high selectivity, neem derivatives affect ca. 400 to 500 species of insect pests belonging to different orders (Schmutterer & Singh 2002), one species of ostracod, several species of mites and nematodes, and even noxious snails and fungi, including aflatoxin-producing Aspergillus spp.

Results of field trials in some major food crops in tropical countries will illustrate the value of neem-based pest management for enhancing agricultural productivity in Asia and Africa.

Rice. The efficacy of neem derivatives against major pests of rice and virus diseases transmitted by them and increases in yield has been reviewed by Saxena (1989). In the Philippines, application of a 2:10 neem cake-urea mixture at 120 kg/ha reduced the incidence of ragged stunt, grassy stunt, and tungro viruses and significantly increased the rice yield more in both dry and wet seasons. Also, weekly ultra-low volume (ULV) spraying of 50% neem oil-custard apple oil mixture in 4:1 proportion (vol/vol) at 8 l/ha from seedling to the maximum tillering stage decreased the tungo incidence and increased the yield (Table 1) (Abdul Kareem et al. 1987). The low input cost of the treatment contributed to a high net gain compared with the insecticide treatment. In India, neem treatments controlled populations of the green leafhopper, the yellow stem borer, the rice gall midge, and grasshoppers. Plots sprayed with 2% neem seed extract at 10 kg/ha yielded the highest grain yield.

Maize, sorghum, and millet. In trials conducted at the Mbita Point Field Station of International Centre of Insect Physiology and Ecology (ICIPE) and in farmers’ fields in Kenya, foliar application of powdered neem seed at 3 g/plant or powdered neem cake at 1 g/plant once at 4 weeks after crop emergence (WE) or twice at 4 and 6 WE to maize, which had been infested with the spotted stem borer, significantly reduced the foliar damage, stem tunneling, tassel breakage, and populations of borer larvae. Grain yield in neem-treated maize plots was as high as that obtained with insecticides and significantly higher than that in untreated control plots (Table 2). Storage of neem cake up to 2 years in the dark did not reduce its pest effectiveness. Similar reduction in pest damage, including their body size (measured by the width of larval head capsules), and increase in yield were obtained when neem cake was applied to sorghum crop (Table 3). In trials conducted in Mali, the use of local neem extract resulted in significant increase in yield of early and main season millet as a result of the control of millet head pests, blister beetle, and head miner.

Banana. The banana weevil, Cosmopolites sordidus, and parasitic nematodes are major pests of banana and plantain. They often occur together and may destroy the corm and the root system, resulting in loss of fruit yield. Most of the highland bananas in Eastern Africa are highly susceptible to the weevil and nematode infestations. Soil applications of neem seed powder or neem cake at 100 g/plant at planting and, subsequently, at 3-month intervals, reduced the populations of the root-lesion nematode, Pratylenchus goodeyi and the root-knot nematodes, Meladogyne spp., on par with Furadan 5G applied at 40 g/plant at planting and then at 6-month-intervals to banana plants grown in 100 l containers with controlled levels of banana nematode infestations (Musabyimana and Saxena 1999a). Eight months after planting, banana plants treated with NC, NSP, kernel powder, or with oil had 7 to 95 times less parasitic nematodes than the untreated control. However, only NC or NSP applied to unpared banana plants kept the nematode population below the economic threshold (Table 4). At 8 months after incorporation into the soil, NC or NSP application was still effective against banana nematodes, while the nematicidal activity of Furadan seemed to decline. Weevil larvae fed little or altogether avoided neem-treated corms, while extensive damage occurred on untreated corms. With neem treatment, fruit yield increased by 27-50% over the control in the first crop and by 30-60% over the control in the second crop, but yield with Furadan during the second crop was even less than that in the control (Musabyimana and Saxena 1999b). Neem application conferred a net economic gain, whereas Furadan application proved uneconomical (Table 4) (Musabyimana et al. 2000).

Grain legumes and vegetables. Because of high profitability of legumes and vegetables, farmers tend to overuse chemicals, which result in hazard to the environment and health of producer and consumer, as well as serious resistance problems. However, neem can provide satisfactory control of insect pests affecting grain legumes and vegetables. A wide range of pests attack cowpea, a major food crop in Africa. Sprays with neem seed extract were quite effective against lepidopterous pests, but weekly “Ultra Low Volume” (ULV) spray applications of neem oil did not control the flower thrips, Megalurothrips sjostedti (Dreyer 1987). On the other hand, in trials conducted at ICIPE’s Mbita Point Field Station and in a farmer’s field in Kenya, applications of 2 or 3% neem seed extract at 200 l/ha at 38, 47, and 51 days after emergence (DE) of cowpea crop or ULV spray applications of 5, 10, or 20% NSE at 10 l/ha significantly reduced the number of thrips larvae in flowers recorded 2 days after each treatment (Saxena and Kidiavai 1997). Also fewer adults occurred in flowers at 51 DE in plots sprayed with 5%, 10% or 20% NSE. Grain yield was significantly higher in plots sprayed with 20% NSE than in control plots and was comparable to yield obtained in plots sprayed thrice with Cypermethrin (Table 5). Because of the low cost of NSE treatment, the net gain was often more when cowpea was sprayed with NSE than with the insecticide. Also, grain quality was superior in neem-treated plots than in control or Cypermethrin-treated plots.

In common beans, high volume spray applications of 2% neem kernel extract at 11-day intervals effectively controlled the chrysomelid beetle, Ootheca benningseni (Karel 1989). Neem derivatives also proved effective against pod borers and bollworms on Bengal gram, against the leaf roller, and flea beetles on okra, and against pod borers and the pod fly on pigeon pea (Saxena 1989).

Kales, cabbages, and other crucifers. Kales, cabbages, and other crucifers are highly vulnerable to attack by the diamondback moth, Plutella xylostella. Synthetic insecticides do not provide long-term control, as the pest is known to develop resistance rapidly (Talekar & Shelton 1993). In trials conducted in Togo, weekly high volume spray applications of 4% methanolic neem kernel extract (NKE) (neem dissolved in methanol) (Adhikary 1985) or even 2.25 to 5% aqueous NKE (Dreyer & Hellpap 1991) almost completely protected the cabbage crop against the pest. Similar results have been obtained in Asia. Other lepidopterous pests of cabbage and aphids are also controlled with neem. In repeated trials conducted at ICIPE Field Station and in a farmer’s field in western Kenya, ULV spray applications of 20% neem seed extract at 10-d intervals, significantly reduced the pest infestation and damage and increased the yield of marketable leaves of kale (‘Sukuma-wiki’ in Kiswahili language) (Table 6) (Saxena unpubl.). Spray applications of 0.3% neem extractive were not as good as neem seed extract treatment. The population of spiders, which are important predators of DBM larvae, was as high in neem-treated plots as in untreated control plots, while it was much lower in Cypermethrin-treated plots. During long rainy seasons, kale leaf yield was significantly higher with neem seed extract than with Cypermethrin. Economic returns with neem seed extract treatments were promising because the cost of neem seed is low.

In Africa, the root-knot nematodes, Meloidogyne spp., and the fruit borer, Helicoverpa armigera are the most damaging pests of tomato. As nematodes are “unseen enemies,” their role in limiting tomato production in tropical regions is generally overlooked. Rössner & Zebitz (1987) and Parveen & Alam (1998) reported nematicidal effects of neem materials in tomato. In field trials conducted at ICIPE’s Field Station at Mbita, Kenya in 1997-98, we found that, compared with untreated control, soil application of neem seed powder at 3 g/hill at planting significantly reduced the number of galls per plant, on par with Furadan 5G (Table 7). However, the nematicidal effects of neem seed powder treatment persisted much longer than that of Furadan. The fruit borer incidence was low, but as a precautionary measure against insect pests in general, neem seed extract, neem extractive, or Cypermethrin was sprayed with a ULV sprayer at 10 l/ha at 10-d intervals. Although fruit yield did not increase significantly with neem or pesticide treatment over the untreated control, the quality of fruits produced in neem-treated plots was distinctly superior. In Niger, weekly spray applications of 5% aqueous neem seed extract reduced the tomato fruit borer damage and increased the marketable fruit yield (Ostermann 1992).

Okra. Pests, such as the leaf-cutting caterpillar, Sylepta derogate, were quite susceptible to spray applications of 0.25% aqueous neem kernel extract (Dreyer 1987) or 5, 10, or 20% aqueous neem seed extract (Cobbinah & Olei-Owusu 1988). Also, the cotton aphid, Aphis gossypii, was well controlled on okra by four weekly sprays of 0.5% aqueous neem seed extract or 2% neem oil; the effects being on par with Butocarboxim insecticide (Dreyer & Hellpap 1991).

In Niger, foliar applications of aqueous neem seed extract at 0.25%, 0.5% or 1% to amaranth fields strongly repelled Spodoptera exigua and a soil drench of 0.5% neem seed extract repelled Spodoptera exigua, while a soil drench of 0.5% neem seed extract repelled Spodoptera littoralis (Ostermann 1992). Spray applications at 0.5% or 1% neem seed extract reduced the foliar damage by S. exigua significantly, while preand post-sowing soil drenches with 0.5% neem seed extract at 1000 l/ha stopped the immigration of S. littoralis larvae into treated fields and almost doubled the leaf yield over that of the untreated plots (Ostermann 1992).

In Sudan, remarkable results were obtained with neem products in the control of the sweet potao whitefly, Bemisia tabaci and the leafhopper, Jacobiasca lybica on potato (Siddig 1987, 1991). Two high volume applications of 2.5% aqueous neem kernel extract sprayed at two-week intervals significantly reduced the pest populations to >50% of the control and increased the yield. The potato tuber moth, Phthorimaea operculella, was unaffected in the field but spray applications of 0.05% and 0.1% of neem oil strongly deterred oviposition and prevented damage in the stored potatoes (Siddig 1988).

Agroforestry and tobacco. Insects and nematodes also affect trees and crops in agroforestry. In collaborative trials conducted by International Centre for Research in Agroforestry (ICRAF) at Shinyanga in Tanzania in 1995-1996, application of powdered neem cake at 2 g/plant to a hybrid maize, “Cargill,” at 4 and 5 weeks after sowing, resulted in a 30% yield increase over the control (ICIPE 1998). Application of neem cake at 135 kg/ha also reduced the termite damage and significantly increased the grain yield of hybrid maize over the Furadan-treated or untreated crop. In a long-term trial conducted at ICRAF Field Station at Machakos, it was observed that when neem cake was applied at 15g/ grevillea seedling, the tree mortality after 15 months was 60%, compared with 52% tree mortality in Furadan treatment, and 72% in untreated control.

In field trials conducted in Tabora, Tanzania, although application of neem seed powder or neem cake at 15 g/m2 was not as effective as Ethylene dibromide at 62 ml/m2 in reducing the root galling index in tobacco plants, the tobacco yield increased significantly with neem treatments (ICIPE 1998).

Pests of Stored Products

Post-harvest losses are notoriously high in developing countries. Worldwide losses in storage reach up to 10% of all stored grain, i.e. 13 million tons of grain lost due to insects or 100 million tons from failure to store properly. Saxena (2002) has reviewed the potential of neem against stored products pests: pests of grain legumes, maize, sorghum, wheat, rice, and potato tubers. At farm-level storage and warehouses, the application of neem derivatives to bags and stored grains has provided protection against insect pests. Powdered neem seed kernel mixed with paddy (1 to 2%) significantly reduced infestation in warehouses. Neem leaves mixed with paddy (2%), bags treated with 2% neem seed extract, or a 20- to 30-cm dried neem leaf barrier between the bags and storage floor significantly reduced insect infestation and damage to grain during a 3-month storage period; the effectiveness being comparable to Methacrifos dust. Likewise, neem seed extract at 7.2 g/90 kg capacity jute bag (100 x 60 cm) controlled 80% of the population of major insects and checked the damage to wheat up to 6 months. The treatment was effective up to 13 months and provided more than 70% protection as compared with untreated control. The neem seed extract treatment was as effective as that of 0.0005% Primiphos methyl mixed with the grain.

The effectiveness of neem oil alone or in combination with fumigants was evaluated against five major species of stored grain pests infesting rice and paddy grains in a warehouse trial conducted in the Philippines (Jilani & Saxena 1988). Rice grain treated with 0.05 - 0.1% neem oil or treated with neem oil after fumigation with Phostoxin, and stored for 8 months had significantly less Tribolium castaneum adults than in the untreated control. Both kinds of treatments were as effective as the bag treatment with Actellic at 25 µg/cm2 or grain treatment with Actellic at 0.0005%, and suppressed the pest population by 60%. The population build-up was also reduced when fumigated or non-fumigated rice was stored in bags treated with neem oil at >1 mg/cm2 . Rhyzopertha dominica, Sitophilus oryzae, Oryzaephilus surinamensis and Corcyra cephalonica were similarly reduced by neem treatments alone or in combination with prior grain fumigation. Fumigation and Phostoxin were effective only for about 2 months against R. dominica, and for up to 6 months against other pest species. In contrast, neem oil treatments were effective up to 8 months. Compared with the pest damage to untreated or fumigated rice, neem oil treatments significantly reduced the damage to rice grain. At 8 months after storage, weevil-attacked grains in neem treatments were 50% of those in the fumigated rice and 25% of those in untreated rice.

Paddy grain that had been fumigated and then treated with neem oil or, after fumigation stored in neem oil-treated bags, also had fewer adults of T. castaneum, R. dominica, S. oryzae, and O. surinamensis, as compared with the fumigated or the untreated paddy grain (Table 8). C. cephalonica infestation was found in the stored paddy only after 4 months and remained low throughout the trial in treated as well as untreated paddy. Neem treatments also decreased the per cent weevil-attacked grains by about 70% or more. Compared with fumigation, which was effective for only 2 months, neem treatments conferred protection against the stored grain pests for up to 8 months, after which the trial was terminated.

In studies conducted in Kenya, the growth and development of 1st-instars of the maize weevil, Sitophilus zeamais, was completely arrested in maize grain treated with neem oil at 0.02%, while the weight loss of treated cobs was less than 1% as compared with 50% reduction in weight of untreated cobs stored for 6 months (Kega & Saxena 1996).

While neem cannot completely replace chemical pesticides used in stored products preservation, the amounts of pesticide needed could be reduced, particularly in developing countries, thereby decreasing the pesticide load in food grains. With proper timing and innovative methods of application, their use could be well integrated in stored products pest management.

Blood-sucking Pests

The effects of neem on hematophagous insects affecting humans and livestock have been reviewed (Ascher & Meisner 1989). Application of paste made from neem leaves and turmeric in 4:1 proportion to the skin cured 87% of the patients suffering from scabies caused by itch mite in 3-15 days. Monthly spray applications of ethanolic extracts of neem or weekly bathing in azadirachtin-rich aqueous 1:20 ‘Green Gold’ controlled the bush tick in Australia, but were less effective against the brown dog tick (Rice 1993). In Jamaica, neem kernel extract controlled ticks on cattle and dogs. In Kenya, engorgement duration of larvae and nymphs of Amblyomma variegatum and larvae of Rhipicephalus appendiculatus were significantly prolonged due to slowed feeding on rabbit host sprayed with neem oil (Table 9) (Kaaya et al. 2007). Neem treatment also led to a reduction in engorgement weight of larvae, nymphs, and adults of A. variegatum, R. appendiculatus, and Boophilus decoloratus feeding on neem-treated rabbits and fewer larvae and nymphs molted to the next developmental stage. Egg masses produced by neem-treated ticks weighed significantly less while hatchability of their eggs was adversely affected. Regardless of tick species, attachment by larvae also was significantly reduced on neem oil-treated rabbits. In trials conducted in pastures in Kenya, application of neem oil on cattle repelled all stages of R. appendiculatus, B. decoloratus, and A. variegatum (Kaaya et al. 2007).

Neem products also repel and affect the development of mosquitoes. Two percent neem oil mixed in coconut oil, when applied to exposed body parts of human volunteers, provided complete protection for 12 h from bites of all anophilines (Sharma et al. 1993). Kerosene lamps containing 0.01-1 percent neem oil, lighted in rooms containing human volunteers, reduced mosquito biting activity as well as catches of mosquitoes resting on walls in the rooms; protection was greater against Anopheles than against Culex. Effectiveness of mats with neem oil against mosquitoes has also been demonstrated; the vaporizing oil repelled mosquitoes for 5-7 h at almost negligible cost. The sandfly also was totally repelled by neem oil, mixed with coconut oil or mustard oil, throughout the night under field conditions. Application of neem cake at 500 kg/ha, either alone or mixed with urea, in paddy fields, was very effective and reduced the number of pupae of Culex tritaeniorhynchus, the vector of Japanese encephalitis, and also resulted in higher grain yield.

Pest Resistance to Neem Materials

A few herbivorous insects, including some sucking insects, some beetles, and some moths do survive on neem but, largely, the tree is free from serious pest problems. Some insects can adapt to limonoids, but in laboratory tests, two genetically different strains of the diamondback moth treated with a neem seed extract showed no sign of resistance in feeding and fecundity tests up to 35 generations (Völlinger 1987, Völlinger & Schmutterer 2002). In contrast, deltamethrin-treated lines developed resistance factor of 20 in one line and 35 in the other. There was no cross resistance between Deltamethrin and neem seed extract in the Deltamethrin-resistant lines. The diversity of neem compounds and their combined effects on insect pests seem to confer a built-in resistance prevention mechanism in neem. However, wisdom demands that users should refrain from exclusive and extended application of single bio-active materials, such as azadirachtin.

Environmental Services and Other Benefits

Environmental Services

Neem in India has been ranked higher than the ‘Kalpavriksha’, the mythological wish-fulfilling tree. Although scientific studies are wanting, neem is reputed to purify air and the environment of noxious elements. During hot summer months in northern parts of the Indian sub-continent, the temperature under the neem tree is -10o C less than the surrounding temperature. Restoration of the health of degraded soils and the ultimate use of such reclaimed wastelands through neem is another example of its value to humans. About 25 years ago, some 50,000 neem trees were planted over 10 km2 on the plains of Arafat to provide shade for Muslim pilgrims during hajj (Ahmed et al. 1989). The neem plantation has had a marked impact on the area’s microclimate, microflora, microfauna, and soil properties, and the full-grown trees provide shade to about 2 million pilgrims. In the last decade, about 25 million neem trees have been grown in southern China, especially in Yunnan province.

The tree is not only beautiful to look at, providing grandeur and serenity, but also serves as a refugia to many beneficial organisms, bats, birds, honey bees, spiders, etc. Honeycombs established on the neem tree are free from galleria wax moth infestation. Many species of birds and fruit-eating bats subsist on the sweet flesh of ripe fruits, while certain rodents selectively feed on the kernel, confirming neem’s safety to warm-blooded animals. The litter of falling leaves improves soil fertility and the organic content. Recently, mycorrhizal associations between neem and bacterial and fungal endophytes have been identified. Indeed, the neem tree is a living microcosm!

The evergreen, perennial tree can survive 250 to 300 years. Even a highly conservative estimate of the intangible ‘environmental service’ rendered by the tree at US $10 per month over its lifetime would give an astonishing value of US $30,000 to $36,000. Other tangible economic uses of neem and the benefits derived, such as biomass production, timber, seed, and honey, are quantifiable.

Reforestation and Agroforestry

Neem is a very valuable forestry species in Asia and Africa and also becoming popular in Tropical America, the Middle East, and in Australia. Nineteenth-century immigrants carried the tree from India to Fiji, and it has since then spread to other islands in the South Pacific, even to Easter Island, which is hardly known as a place for trees. Being a hard, multipurpose tree, it is ideal for reforestation programs and for rehabilitating degraded, semiarid and arid lands, and coastal areas. During a severe drought in Tamil Nadu, India, in June-July 1987, it was witnessed that neem grew luxuriantly, while other vegetation dried up.

Neem is useful as windbreaks. In areas of low rainfall and high wind speed, the neem tree can protect crops from desiccation. In the Majjia valley in Niger, over 500 km of windbreaks comprised of double rows of neem trees have been planted to protect millet crops, which reportedly resulted in a 20% increase in grain yield. Neem windbreaks on a smaller scale have also been grown along sisal plantations in coastal Kenya. Large-scale planting of neem has been initiated in Kwimba Afforestation Scheme in Tanzania and at Adjumani in northern Uganda.

In countries from Somalia to Mauritania, neem has been used for halting the spread of the Sahara desert. Also, neem is a preferred tree along avenues, in markets, and near homesteads because of the shade it provides. However, neem is best planted in mixed stands. It was probably no coincidence that Emperor Ashoka, the great ruler of ancient India in the 3rd century BC, commanded that neem be planted along the royal highway and roads along with other perennials – tamarind and ‘mahua’. Neem has all the good characters for various social forestry programs.

Neem is an excellent tree for silvipastoral systems involving production of forage grasses and legumes. But according to some reports, neem cannot be grown among agricultural crops due to its aggressive habit. Others say that neem can be planted in combination with fruit cultures and crops such as sesame, cotton, hemp, peanuts, beans, sorghum, cassava, etc., particularly when neem trees are still young. The neem tree can be lopped to reduce shading and to provide fodder and mulch. Recent advances in tissue culture and biotechnology should make it possible to select neem phenotypes with desirable height and stature for use in intercropping and various agroforestry systems. The allelopathic effects of neem on crops, if any, need to be investigated.

Biomass Production and Utilization

Full-grown neem trees yield between 10 to 100 tons of dried biomass/ha, depending on rainfall, site characteristics, spacing, ecotype or genotype. Leaves comprise about 50% of the biomass, while fruits and wood constitute one-quarter each. Improved management of neem stands can yield harvests of about 12.5 cubic meters (40 tons) of high quality wood/ha.

Neem wood is hard and relatively heavy and is generally used for making carts, tool handles, farm implements, toys, and religious icons in some parts of India. The wood seasons well, except for end splitting. Being durable and termite resistant, neem wood is used in making fence posts, poles for house construction, furniture, etc. There is a growing market in some European countries for light-colored neem wood for making household furniture. Pole wood is especially important in developing countries; the tree’s ability to re-sprout after cutting and to re-grow its canopy after pollarding makes it useful for pole production. Neem grows fast and is a good source of firewood and fuels; the charcoal has high calorific value.

Neem for Mitigating Rural Poverty

Poverty is not necessarily the want of money or cash in hand. In a wider sense, it is the lack of options, whether it is the non-availability of fertilizer for crop cultivation or pesticides for crop protection, medical remedies for family welfare, fuel or firewood for cooking, timber for furniture or dwelling, or the availability of appropriate technology for restoring wastelands, or absence of income generation and employment opportunities. In all these respects, neem could be a ‘panacea,’ particularly in rural areas. In India, during the neem fruiting season in June-July, seed collection provides employment and income to unemployed women, children, and infirm people. With growing demand worldwide for neem seed, neem honey, and other neem products, there is substantial scope for establishing cottage industries, and other smallscale enterprises in rural areas of Asia and Africa where neem is widespread. Since agriculture is the staff of life in rural areas, enhanced agricultural productivity through the use of neem products in pest management could significantly contribute to alleviation of poverty in rural areas.

Recent Developments on Neem in the Developed World

For nearly the past three decades, neem has come under close scientific scrutiny as a source of natural insect control material in numerous international conferences, mostly held in developed countries such as Germany, Canada, Australia, USA, etc. Nearly 3000 scientific papers have been published to date on neem. Australia, with its large tracts of unused arid and semiarid lands, may become a major grower of neem in the next couple of decades.

The interest in neem in the developed world is attributable to the fact that neem-based pest control products with diverse modes of action are not only effective against pests, but also inherently safer, less persistent in the environment, and less prone to the problem of pest resistance than the synthetic pesticides. Technical grade neem active ingredients, principally azadirachtins, fetch the highest price, about US $375/ kg as compared with US $75/kg for pyrethrum (Isman 1995). In 1989, the use of ‘Margosan’, containing 0.3% azadirachtin, was granted approval from the US Environmental Agency for non-food uses on ornamentals and landscape plants; in 1993 EPA approved the use of neem products, such as ‘Neemix’ on food crops. The U.S. based W.R. Grace Co., which holds patents from the U.S. Patent and Trademarks Office on the method of extracting the insecticide from neem, is advertising ‘Neemix’ as a “modern technology from ancient trees.” Agridyne, another U.S. based company, is marketing ‘Align’ (with 3% azadirachtin and 97% inert ingredients, mainly other neem limonoids) for control of insect pests in vegetable, fruit, nut, and agronomic crops. Both products are now being used for commercial-scale crop protection in the USA. Neem seed extracts are being used for forest insect pest management in Canada. Neem-based pesticides are expected to capture 10% of the global pesticide market in the next decade. A technique using a neem extract as a fungicide has also been patented in the USA. Worldwide, nearly 50 patents have been granted on neem so far. The use of additives, adjuvants, activators, and even Bt are being examined for potentiating the activity of azadirachtins against insect pests.

The patenting of neem pesticides and their formulations has evoked serious criticism and challenge in the developing world, particularly in India, as an example of ‘folk wisdom piracy’. Efforts were made in some European countries to extract azadirachtin on a commercial scale from neem calli. But such ventures remained nonviable and economically unjustifiable. Quality neem seed with high azadirachtin content would remain the basic raw material for production of neem-based insecticides of the future. In that context, tropical countries of Asia and Africa could become major exporters of the raw material or even value-added finished products.

Conclusion

In the coming decades, the developing world would be facing four distressing crises, all counter-productive impacts of increased human activity and failure to use natural resources in a sustainable manner: 1. Threat to food security due to population pressure, 2. Rural and urban poverty and joblessness, 3. Pollution and degradation of arable land and water bodies, and 4. Loss of biodiversity. Neem has much to offer in solving global agricultural, public health, population, and environmental pollution problems. Certainly, it cannot be achieved without building awareness of its potential and dissemination of neem-based technology, whether for pest management, public health, reforestation, or production and commercialization of various neem products for domestic use or exports. More neem trees of superior ecotypes or genotypes will have to be grown, particularly as a strategy for restoring marginal lands and making them productive and remunerative. Certainly, this would not happen overnight. If we are planning for long-term sustainability, then an investment in a time frame of five to 10 years is insignificant. Also, financial support, backed by favorable policies for neem promotion, production, and commercialization will be necessary.

As pointed out above, the demand for neem products, especially the seed as the basic raw material, is going to increase by leaps and bounds. Herein also lies a solution for creating income generation and job opportunities in rural and tribal areas. Neem-based industries in urban and industrialized regions would also create job slots for producing value-added products for domestic consumption and exports. Neem should also play a significant role in enriching the floral and faunal biodiversity, as a huge variety of organisms, from insects to birds and mammals subsist on neem. Increased planting of neem along roadsides and avenues should make cities more liveable and make rural areas more attractive than now. Use of neem-based pest control agents and fertilizers should reduce pesticide-related hazards and pollution on land and in water bodies. In fact, the neem story is just unfolding. Tropical countries where neem can thrive have much to gain from increased awareness of neem’s hidden ‘treasures’.

Glossary of Terms

• Neem seed powder: the ground and dried powder of the neem seed (includes oil, active ingredients, and seed cake)

• Neem seed cake: the residue cake (or solids) left over from the seed kernel when it is pressed or expelled to separate the oil

• Neem kernel powder: the ground and dried powder of the neem seed kernel (includes oil, active ingredients, and seed cake)

• Neem oil: the oil extract from the seed kernel when it is pressed or expelled

• Neem seed extract- the oil extract from the seed kernel when it is pressed or expelled

• Neem extractive: the extract of various liquids from parts of the neem plant, including its leaves and seeds, which are azadirachtin-rich

• Methanolic neem kernel extract: the extract of active ingredients of the neem seed kernel using alcohol as the solvent

• Aqueous neem kernel extract: the extract of active ingredients of the neem seed kernel using water as the solvent

References

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Adhikary, S. 1985. Results of field trials to control the diamond-back moth, Plutella xylostella L. in Togo by application of crude methanolic extracts of leaves and kernels of the neem tree, Azadirachta indica A. Juss, in Togo. Z. Angew. Entomol. 100: 27-33.

Ahmed, S., S. Bamofleh, & M. Munshi. 1989. Cultivation of neem in Saudi Arabia. Econ. Bot. 43: 35-38.

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Kaaya, G. P., R. C. Saxena, & S. Gebre. 2007. The potential of neem products for control of economically important African ticks. Biosciences, Biotechnol. Res. Asia, 4: 95-104.

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Author’s Contact Information

Dr. Ramesh C. Saxena Chairman, Neem Foundation G-152, Palam Vihar, G urgaon, India, 122 017

Tel.: 91-124-2360870, 9811573439;

E-mail: susaxena@sify.com

[Editor’s Note: The neem tree truly is a miraculous plant with much potential for helping smallholders in agriculture and community development to strengthen livelihoods. ECHO has been researching and promoting neem since the early 1980’s and has quite a repertoire on www.echocommunity.org related to neem, including this early Technical Note from 1984. As with all ECHO techniques, ideas and information, we encourage you to try these various ideas and options after further research and in a low-risk setting to your beneficiaries. Remember that agriculture and culture are context-sensitive, and what may work well in once context might not in another. Please do let us know your successes and failures as you seek to see how neem might fit into your sustainable pest management and environmental conservation work!

Regarding the distribution of neem seeds, the ECHO Asia Seed Bank does not routinely keep seeds on hand, as they rapidly loose their ability to germinate, but the Seed Bank can source neem seeds seasonally from our partner organizations in Thailand. If you are interested in neem seeds, kindly e-mail asiaseeds@echonet. org.]