Azadirachta indica (neem tree)

Azadirachta indica, grown pantropically, has received worldwide attention in recent years. It is considered to be a 'wonder' tree with an unlimited number of uses. The Swahili name for the tree ‘ mwarobaini ’ comes from the word for forty since it has at least 40 uses. A report prepared by an ad hoc advisory panel has called it “a tree for solving global problems” (Vietmeyer, 1992). The tree has great religious, economic, medicinal and ornamental value, and nearly every part of the tree (roots, trunk, bark, leaves, flowers, fruits and seeds) can be used for some purpose ( Tewari, 1992 ; Luna, 1996 ). Commonly known as 'neem', A. indica can be grown under a range of climatic and soil conditions. Its native range is India into Malesia as far as Java ( PIER, 2024 ). It produces timber, fuelwood, fodder, medicines, pesticides and oil. It is said that the value of its byproducts is greater than that of its wood and serves the role of 'village dispensary' (Vietmeyer, 1992; Gupta, 1993 ; Siddiqui, 1995 ). It is seldom leafless and the shade it provides in dry, hot climatic regions of India and Pakistan is highly valued. There are an estimated 18 million neem trees in India and Pakistan, most of them lined along roadsides or clustered around the backyards of houses and markets, providing relief from the sun (Vietmeyer, 1992).

Azadirachta indica has been extensively introduced throughout tropical and subtropical regions. However, it has become invasive in only a fraction of the countries where it is cultivated and utilized as a multi-purpose tree. Although it does not possess some of the attributes of other invasive species, e.g. long seed viability and ability to compete with other plants in the seedling stage, it does produce seed prolifically, and seed dispersal is often aided by birds and mammals. This has allowed it to become a serious problem in the native forests of several African and Caribbean countries. A. indica has been described as a moderately invasive species.

Meliaceae is a woody family of plants comprising 50 genera and about 640 species widely distributed throughout the tropics and subtropics, with only slight penetration into temperate zones ( Muellner et al., 2005 ; Stevens, 2012 ). Species in the genus Azadirachta are closely related to and sometimes confused with species of the genus Melia . However, an easy distinction can be made between the two genera based on leaf and ovary morphology: Azadirachta spp. have simple pinnate leaves with a pair of orbicular glands and a pair of elongated glands at the base and by the 3-locular ovary, while Melia spp. possess 2- to 3-pinnate leaves with one pair of orbicular glands and a 4- to 8-locular ovary ( Lemmens et al., 1995 ). The name Azadirachta is derived from the Persian name of the tree, azad-darakht-i-hindi. Azadirachta has two species, A. indica, thought to be native to dry areas within the Indo-Pakistan subcontinent and possibly Myanmar (Lemmens et al., 1995) and A. excelsa, native to Southeast Asia.

In Thailand, A. indica var. siamensis, was recognized by Valerton, but no infraspecific taxa are recognized in the most recent treatment of the genus by Mabberley et al. (1995) .

Azadirachta indica is a medium to large, deep-rooted, evergreen tree, to 15(30) m tall, with a round or oval, large dense crown to 10(20) m in diameter; wide spreading glabrous branches; bole branchless for up to 7.5 m, 1.5-2.8 m in girth, sometimes fluted at base; bark moderately thick (1.2-2.5 cm), with small, scattered tubercles, deeply fissured and flaking in old trees, dark grey outside and reddish inside, with colourless, sticky foetid sap. The tree generally branches early in life, forming a broad round crown of bright green foliage. The seedlings have a moderately long and tapering primary root with the lateral roots average in number and length, and fibrous ( Troup, 1921 ). However, mature A. indica trees have comparatively short tap roots depending on the soil, and a number of long, horizontal lateral roots. Heartwood is red and hard.

Leaves alternate, crowded near the end of branches, simply pinnate, 20-40 cm long, exstipulate, light green, with two pairs of glands at the base, otherwise glabrous; petiole 2-7 cm long, subglabrous; rachis channeled above; leaflets 8-19, very short petioluled, alternate proximally and more or less opposite distally, ovate to lanceolate, sometimes falcate (2) 3.5-10 × 1.2-4 cm, glossy, serrate; apex acuminate; base unequal. They are generally crowded near the branch end. The leaflets comprise four to seven pairs on each leaf; they are oblique, lanceolate, coarsely serrate, glabrous on both surfaces and 2.5-7.5 cm x 1.2-4.0 cm in size. The base of leaflets is asymmetric and acuminate, with very short petioles ( Parker, 1956 ; Sheikh, 1993 ).

Inflorescence an axillary, many-flowered thyrse, up to 30 cm long; bracts minute and caducous; flowers bisexual or male on same tree, actinomorphic, small, pentamerous, white or pale yellow, slightly sweet scented; calyx lobes imbricate, broadly ovate and thin, puberulous inside; petals free, imbricate, spathulate, spreading, ciliolate inside. The flowers are small, bisexual and male on the same tree. They occur in dense bunches with lanceolate, caducous bracts. The calyx is puberulous outside and 5-lobed to the lower half. The lobes are imbricate, round-ovate and minutely ciliolate. The petals are free, imbricate, 6 mm long, obovate to oblong, faintly puberulous, and ciliolate outside. The staminal tube is 3-5 cm long, cylindrical, slightly expanded at the mouth and glabrous. The tube ends with ten rounded, truncate, emerginate, or bilobed appendages, which are apiculate, inserted at the base and opposite to appendages. The stigma is expanded to form a ring with three acute, partially fused, papillose stigmatic lobes included in the staminal tube. Ovary sub-globose.

Fruit 1 (or 2)-seeded drupe, ellipsoidal, 1-2 cm long, greenish, greenish-yellow to yellow or purple when ripe; exocarp thin, mesocarp pulpy, endocarp cartilaginous with inter-cellular space between the epicarp and endocarp; seed ovoid or spherical, reticulate; apex pointed; testa thin, composed of a shell and a kernel (sometimes two or three kernels), each about half of the seed’s weight. The outer seed coat has thick-walled epidermis and three layers of loosely arranged cells, with the cell of the inner integument elongating tangentially to form the inner seed coat ( Parker, 1956 ; Tewari, 1992 ; Luna, 1996 ; Orwa et al., 2009 ; Flora of Pakistan Editorial Committee, 2024 ; PIER, 2024 ; PROTA, 2024 ).

The tree starts fruiting at an age of about 5 years, but economic yield of fruit is obtained at an age of 10-12 years. A. indica may live for 200 years ( PROTA, 2024 ). There are 3300-4500 seeds per kilogram, and on average a medium-sized tree produces 37-55 kg of fruit ( Streets, 1962 ; Luna, 1996 ). Germination of the seed is about 55% after 11-14 days ( Parker, 1956 ; Pirani, 1994 ). In very dry localities or during the periods of extreme drought, A. indica can become almost entirely leafless for a brief period. The new leaves appear in March-April before the old leaves have fallen. It remains in full leaf during the summer when the shade is most needed ( Hocking, 1993 ; Luna, 1996 ). Depending on climatic conditions, flowering has been seen to occur at various times throughout the year. In the hot and dry subtropical areas of Pakistan, A. indica flowers in early summer and its fruit develops during the rains from June to August ( Tewari, 1992 ). In Thailand, A. indica trees flower from December to February and fruit in March to May ( Lemmens et al., 1995 ). In the Sahel, fruits of A. indica ripen from November to February whilst in India, fruits ripen from May to August ( PROTA, 2024 ).

There is much confusion in the literature about the natural distribution of A. indica . It is considered to be native to dry areas in Afghanistan, Pakistan, India, Sri Lanka, Bangladesh, Myanmar and China ( Abdulla, 1972 ; Tewari, 1992 ; Vietmeyer, 1992; Gupta, 1993 ). It is cultivated as well as naturalized in Thailand, Malaysia and Indonesia. The World Agroforestry Centre (2002) reports that it may have originated in Myanmar and from there became naturally distributed across the Indian subcontinent. In India and Pakistan, A. indica occurs naturally in dry deciduous and thorn forests ( Champion et al., 1965 ). Its altitudinal range is 0-1500 m ( Webb et al., 1984 ; Tewari, 1992 ). More recently, it has been planted in Peninsular Malaysia and Singapore, the Philippines, Australia, Saudi Arabia, tropical Africa, the Caribbean, and Central and South America (see Distribution Table for details).

Azadirachta indica has been successfully planted in Sudan, Saudi Arabia and Sahelian zones of Africa as well as in Mauritania, Somalia, Sierra Leone, Malawi, Zimbabwe, Tanzania, Zanzibar and non-Sahelian areas of Guinea, Nigeria and Ghana. A. indica has also been successfully introduced in Fiji, Thailand, Malaysia, Indonesia, the Philippines, Australia, the Caribbean, Central and South America and southern USA ( Streets, 1962 ; Tewari, 1992 ; Vietmeyer, 1992). The largest nearly pure stand of A. indica is probably in Saudi Arabia, where about 50,000 plants have been raised on the Plains of Arafat near Makkah (Vietmeyer, 1992).

Azadirachta indica has been successfully introduced throughout Africa, the Middle East, Southeast Asia, Australia, the Pacific islands, the Caribbean, Central and South America and the southern USA ( Streets, 1962 ; Tewari, 1992 ; Vietmeyer, 1992). The largest nearly pure stand of A. indica is probably in Saudi Arabia, where about 50,000 trees have been raised on the Plains of Arafat near Makkah (Vietmeyer, 1992). Most of these introductions occurred during the 1800s. During this century, it was taken to Fiji, Mauritius and Guyana by Southeast Asian emigrants, and to Egypt, East Africa and sub-Sahelian West Africa by the British and has become one of the most rapidly spreading trees with a wide distribution through the tropics and subtropics ( World Agroforestry Centre, 2002 ; PROTA, 2024 ).

Azadirachta indica is reported to have become invasive in some of the countries where it has been introduced. For example, it has been listed as invasive in Puerto Rico ( Federal Highway Administration, 2001 ) where it is associated with dry grounds in the Dominican Republic ( IABIN, 2003 ) and several other Caribbean countries. It has invaded endemic coastal forests in Kenya (Hamilton A, World Wide Fund for Nature, Godalming, UK, personal communication, 2002), and is widespread in Ghana (Cobbinah J, Forestry Research Institute of Ghana, personal communication, 2003) where a programme to monitor its invasiveness was begun ( Chamberlain, 2000 ). It is a weed in the Gambia where it is becoming established in natural forests at the expense of native trees ( WRM, 1999 ). Its ability to spread rapidly has also been reported to cause problems in Senegal ( Chamberlain, 2000 ), notably in the southern Casamance region and also in neighbouring Guinea Bissau, where it was already considered a nuisance weed in 1995 (Pasiecznik N, CAB International, personal communication, 2004).

In Northern Territory, Australia, there are indications that A. indica is escaping from plantations (Reilly D, Department of Business Industry and Resource Development, Government of Australia, personal communication, 2002) and it is also described as a weed of concern in Arnhem Land ( Anon., 1998 ). In Brazil, it was officially introduced in 1986, and since the 1990s, the species has been cultivated commercially in the Southeast, Midwest, North and Northeast of Brazil ( Freire et al., 2013 ).

The widespread introduction of A. indica across the tropics and subtropics means that in most countries where invasion is possible, the species will already have been introduced. It has, however, become invasive in certain parts of its introduced range, and monitoring of this species in areas of higher rainfall may appear merited.

Azadirachta indica spreads by seeds and vegetatively by root suckers. The seeds drop from the tree and germinate in their resting place. In Africa, A. indica dispersal has been facilitated by birds and mammals such as baboons, birds, bats and terrestrial mammals are known to eat the fruits and disperse the seeds throughout the native range. Shifting cultivation and logging practices may have contributed to the spread of A. indica in Ghana by making available open, disturbed land for colonization ( Chamberlain, 2000 ). A. indica is frequently self-sown in gardens and the areas under mature trees are quickly colonized by a carpet of seedlings.

Azadirachta indica is sometimes confused with closely related species of Melia, but an easy distinction can be made between the two genera based on leaf and ovary morphology. Azadirachta spp. have simple pinnate leaves with a pair of orbicular glands and a pair of elongated glands at the base and by the 3-locular ovary, while Melia spp. possess 2- to 3-pinnate leaves with one pair of orbicular glands and a 4- to 8-locular ovary ( Lemmens et al., 1995 ). Azadirachta has two species: A. indica and A. excelsa . The latter is a larger tree with larger leaves having 14-23 leaflets with entire margins ( PROTA, 2024 ).

Azadirachta indica is commonly cultivated in semi-arid to wet tropical and subtropical regions ( PIER, 2024 ). In India and Pakistan, A. indica occurs naturally in dry deciduous and thorn forests ( Champion et al., 1965 ), and grows in mixed forests with Acacia species and Dalbergia sissoo in India ( World Agroforestry Centre, 2002 ). In its exotic range, it is reported to have become invasive in a number of habitats including fallow agricultural land, savannah, and dry and arid forests (Hamilton A, World Wide Fund for Nature, Godalming, UK, personal communication, 2002), coastal forest in Ghana ( Chamberlain, 2000 ), lowland monsoon forest in Indonesia and evergreen forest and dry deciduous forest in Africa ( World Agroforestry Centre, 2002 ). The species can grow on dry, infertile sites, but grows best when it has adequate water ( PIER, 2024 ).

Two chromosome numbers have been recorded for this species, 2n=30 in root tip mitosis and 2n=28 ( Tewari, 1992 ). The genetic potential of A. indica has not been fully assessed. A marked difference in the yield of azadirachtin has been observed from different seed sources ( Siddiqui, 1995 ), with seed from Ghana yielding 3.5 g/kg whereas Indian seed yielded only 0.2 g/kg. Therefore, genetic improvement studies should be undertaken to utilize the genetic variation in the species, including selection of A. indica plus trees for important traits, general growth, medicinal, insecticidal, anti-feedant and pesticidal characteristics, maturity and yield of fruits and properties and yield of oil. Provenance studies should also be carried out to determine suitable seed sources for various localities, though care should be exercised, because it is difficult to distinguish between natural stands and artificial plantations of this species.

In many of the areas where A. indica has been introduced, unspecified Indian/Pakistani seed sources have been used. Therefore, provenance seed collection should be carried out in distinct populations of this species. An International Consultation on Establishment of Provenance Trials of this species was constituted by the FAO in 1993 to assist a number of countries to select suitable seed sources for planting. On the basis of results of progeny tests of plus trees and provenance studies, seed orchards could be established. Studies on mutation and breeding of polyploids, as well as vegetative propagation and tissue culture, also need to be carried out as they hold great potential for genetic improvement ( Tewari, 1992 ; Parveen et al., 1995 ).

Azadirachta indica starts fruiting at about 5 years of age, but economic yield of fruit begins at 10-12 years. There are 3300-4500 seeds per kg, and on average a medium-sized tree produces 37-55 kg of fruit ( Streets, 1962 ; Luna, 1996 ). Fruit ripening coincides with the rainy season and under natural conditions, the fruit falls on the ground and germinates within 15 days. On very dry sites or during the periods of extreme drought, A. indica can become almost entirely leafless for a brief period and new leaves appear in March-April before the old leaves have fallen, but it always remains in full leaf during the summer when the shade is most needed ( Hocking, 1993 ; Luna, 1996 ). Depending on climatic conditions, flowering has been seen to occur at various times throughout the year. In the hot and dry subtropical areas of Pakistan, A. indica flowers in early summer and its fruit develops during the rains from June to August ( Tewari, 1992 ). In Thailand, A. indica trees flower from December to February and fruit in March to May ( Lemmens et al., 1995 ). The life span may be some 200 years ( World Agroforestry Centre, 2002 ). A. indica seedlings are unable to compete with other plants, and grasses present a particular problem in early establishment, however, they are able to withstand shade during the early years of development ( World Agroforestry Centre, 2002 ).

Azadirachta indica produces bisexual flowers or male flowers on the same tree. Flowers are pollinated by insects including bees ( Apis spp.), and there are indications of self-incompatibility ( World Agroforestry Centre, 2002 ). There are large quantities of seed and on average a medium-sized tree produces 37-55 kg of fruit per year ( Streets, 1962 ; Luna, 1996 ). In Puerto Rico, where the species is invasive, germination of fresh seeds is 98-100% ( Federal Highway Administration, 2001 ), but seeds have a short viability of about 3-4 weeks, and germination falls to about 55% after 11-14 days ( Parker, 1956 ; Pirani, 1994 ). Birds and bats play an important role in dispersal of the seed. Baboons can act as major dispersers in some areas, e.g. in the Shai Hills Game Production Reserve in Ghana ( Chamberlain, 2000 ), and germination is enhanced by passage through the baboon guts ( Mabberley, 1997 ). A. indica is frequently self-sown in gardens and the areas under mature trees are quickly colonized by a carpet of seedlings. It has the ability to establish itself under the protection of thorny bushes and to survive in dry poor soils, provided it is not subjected to frost ( Tewari, 1992 ). Although the main reproduction is by seed, root suckering does occur, for example when the roots are damaged.

In India and Pakistan, A. indica occurs naturally in dry deciduous and thorn forests ( Champion et al., 1965 ). In India, A. indica can be found growing with species of Acacia and Dalbergia sissoo ( World Agroforestry Centre, 2002 ). In Indonesia, it is naturalized in lowland monsoon forest, whilst in Africa, it is found in evergreen forest and in dry deciduous forest ( PROTA, 2024 ).

Azadirachta indica has wide climatic adaptability and thrives under sub-humid to semi-arid and arid climatic conditions. It grows at temperatures as low as 1°C and as high as 49°C ( Siddiqui, 1995 ), though it is generally found in areas with mean maximum temperatures of 26-38°C, mean minimum temperatures of 24-28°C and mean annual temperatures of 24-32°C. The seedlings are liable to be killed by frost . A. indica requires large amounts of light but tolerates fairly heavy shade during the first few years ( PROTA, 2024 ). It is a species of arid and semi-arid tropical and subtropical ecological zones, with a mean annual rainfall of 450-1150 mm. However, in the Thar Desert of Pakistan, A. indica tolerates as little as 113 mm rainfall per year ( Siddiqui, 1995 ) and a dry season up to 8 months long. When found growing where annual rainfall is as little as 130 mm, it often receives supplementary water by virtue of its situation, i.e. in a wadi bed, or depression, or a shallow water table. 2500 mm is tolerated on well-drained soils, but fruiting is generally poor ( PROTA, 2024 ). A modified description of climatic requirements (see climatic data table of this data sheet) was prepared by CSIRO ( Booth and Jovanovic, 2000 ).

Azadirachta indica has an altitudinal range of 0-1500 m ( Webb et al., 1984 ; Tewari, 1992 ), however it grows better at low altitudes. The tree grows on a variety of soils, clayey or sandy, saline or alkaline. Experimental results confirm that neem plants can be grown in moderate saline soils ( Akram et al., 2024 ). It does particularly well, however, on black cotton soils and deep, well drained soils with good subsurface water. Unlike most other multi-purpose tree species, A. indica thrives on dry, stony, shallow soils and even on soils with hard calcareous or clay pans at a shallow depth ( Tewari, 1992 ). It will not grow on waterlogged soils or in deep dry sands where the dry season water table lies below 18 m ( PROTA, 2024 ). The tree improves soil fertility and water holding capacity because it has the unusual property of calcium mining, thereby neutralizing acidic soils. Its extensive root system also has a rare physiological capacity to extract nutrients from highly leached sandy soils. A. indica can grow on soils with a wide pH range. The optimum growth is at pH 6.2 to 7, but it can also grow well down to pH 5 and survives in soils between pH 3 and 9 ( Lemmens et al., 1995 ).

The fruits, seeds, and foliage of A. indica contain several compounds that repel or kill insects, inhibit the growth and development of fungi, and limit the infective ability of plant viruses. Despite this, a number of pests and diseases have been reported on this species ( Pirani, 1994 ; Siddiqui, 1995 ). A comprehensive review of pests and diseases of neem is provided by Boa (1995) .

Damping off affects germinating seedlings under conditions of excessive moisture. In India, up to 20% seedling mortality has been reported in nurseries at New Forest, Dehra Dun. The fungus Fusarium oxysporum is generally associated with diseased seedlings ( Pirani, 1994 ; Siddiqui, 1995 ).

Several fungi that attack foliage can cause damage in nurseries. Rhizoctonia leaf web blight is caused by the fungus Rhizoctonia solani [ Thanatephorus cucumeris ], and forms grey-brown spots on foliage. Infected leaves are joined together by fungus hyphae, as if caught in a spider's web. This disease is common in nurseries after the monsoon rains begin. Infection by Glomerella cingulata, also results in leaf spots that rapidly increase in size and cover large areas of foliage surface. Other fungi that damage foliage in nurseries are Alternaria alternata and Pseudocercospora subsessilis .

Several bacteria, including Pseudomonas viticola [ Xanthomonas campestris pv. viticola ], P. azadirachtae [ Xanthomonas campestris pv. azadirachtae ] and Xanthomonas azadirachtin, cause leaf spot diseases ( Tewari, 1992 ).

Root rot is caused by the fungus Ganoderma lucidum . This fungus has a worldwide distribution and a broad host range. Sporadic infections occur in young plantings of this species when stumps and roots of the previous tree crop are not removed from the site. The fungus attacks the sapwood and causes a white spongy rot. Symptoms of infection are pale, thin foliage and branch dieback. Fruiting bodies often occur at the base of the stem (Vietmeyer, 1992; Pirani, 1994 ).

Azadirachta indica is one of many plants affected by pink disease caused by the fungus Corticium salmonicolor [ Phanerochaete salmonicolor ]. This disease can cause serious damage, especially under tropical conditions ( Hocking, 1993 ). The earliest sign of infection is the presence of white or pink pustules on dead bark. A conspicuous pink layer of fungus mycelium spreads over the bark. In time, the bark may be entirely destroyed and the outer layers of wood killed. Branches are killed quickly causing the foliage to wilt and turn black.

The fungus Botryodiplodia theobromae [ Lasiodiplodia theobromae ] is associated with weeping cankers and dieback of neem in Niger ( Boa, 1995 ).

Azadirachta indica is one of many hosts of the mistletoe Dendrophthoe falcata, which is widely distributed in the Indo-Pakistan subcontinent and the Solomon Islands. Another mistletoe of the genus Tapinanthus also infests neem and other trees in Nigeria ( Pirani, 1994 ; Boa, 1995 ; Luna, 1996 ). This mistletoe is capable of killing branches and causing deformity.

A decline of neem, due to a complex of factors, has been reported from several countries in West Africa. The most conspicuous symptom associated with this condition is loss of older foliage, which is often preceded by yellowing of older leaves. Foliage loss gives tree crowns an open appearance with clumps of leaves concentrated at the branch tips. This symptom has been termed ‘giraffe's neck’ ( Boa, 1992 ; Ciesla, 1993 ). Neem decline was first reported from Niger in 1990 but was subsequently observed in northern Nigeria, Chad and the Cameroon ( Boa, 1995 ). The condition was probably related to long-term moisture stress. Symptoms were significantly reduced following the 1994-1995 rainy season, which was much heavier than previous years (WM Ciesla, Forest Health Management International, Colorado, USA, personal communication, 2004).

Fire ants, Solenopsis sp. (Hymenoptera: Formicidae) have caused severe defoliation of three- to six-year-old trees in Andhra Pradesh, India. A. indica was the only plant fed upon, even though other plants were available. In Central and South America, leaf-cutting ants ( Acromyrmex spp.) are common defoliators.

Loopers (Lepidoptera: Geometridae), including the widely distributed species, Ascotis selenaria, have occasionally been reported as defoliators, Boarmia variegata also defoliates A. indica in nurseries in India. Caterpillars of the genus Eucema (Lepidoptera: Pieridae) also have been reported as defoliators ( Pirani, 1994 ; Luna, 1996 ).

The powder post beetles Apate monachus and A. terebrans (Coleoptera: Bostrichidae) are native to most of Africa, and have a wide range of host plants, including A. indica . The larvae feed on the sapwood of dead trees and logs and reduce the wood to a fine powder. Adults attack young trees and bore into small stems and branches. This either kills trees directly or makes them susceptible to mechanical injury. Both species have been introduced to the Caribbean Islands and Brazil ( Hocking, 1993 ; Pirani, 1994 ).

Laspeyresia aurantiana (Lepidoptera: Olethreutidae) is a shoot borer and foliage feeder of neem. Boring can kill buds and cause excessive branching. In some cases, up to 55% of A. indica shoots have been infested by L. aurantiana ( Pillai and Gopi, 1990 ).

Several species of termites have been reported from neem. These are sometimes locally damaging, but do not kill living trees.

Sucking insects constitute the largest group of insects that infest A. indica . At least 20 species, representing nine families, have been recorded. They feed on the foliage, branches and stems of host plants. This causes desiccation of plant tissue and results in drying of the foliage, defoliation, stem and branch dieback, and occasional tree mortality ( Tewari, 1992 ; Gupta, 1993 ; Pirani, 1994 ; Boa, 1995 ). Some species have salivary toxins that accelerate damage and tree death.

The tea mosquito, Helopeltis antonii (Heteroptera: Miridae), attacks the terminal shoots of neem. Feeding causes drying of the foliage and terminal shoots. This is believed to be due to a phytotoxic reaction to the saliva of the feeding insects. While large trees tend to recover, heavy infestations have been shown to cause seedling mortality. Widespread damage from this insect has been reported in southern India ( Browne, 1968 ). In Karnataka, severe incidence has been reported with adults and nymphs found desapping the tender parts of the twigs resulting in black patches and gummosis on the feeding zone initially. Later, affected twigs were found drying and leaves showing a burnt appearance ( Shankara et al., 2023 ). H. antonii is also a pest of cashew, Anacardium occidentale, plantations, and it is believed that large numbers of insects are carried by northeast monsoons from cashew to neem plantations from October to December. In addition, A. indica is highly infected by the seasonal pest Helopeltis theivora ( Shankar et al., 2022 ).

The Oriental yellow scale or cochineal, Aonidiella orientalis (Homoptera: Diaspididae) has caused widespread damage to neem in parts of Africa and India. This insect attacks the foliage and young stems. Heavy feeding gives trees a burnt appearance. A. orientalis has a wide distribution and has been reported in China, Southeast Asia, Africa, Australia, the Indian subcontinent, Iran, the Arabian Peninsula, Florida, USA and the Caribbean. It is found primarily on citrus and other tropical fruit trees. There is a report of a 1935 occurrence of A. orientalis on A. indica in the Sudan, and in 1972, an infestation was recorded in Cameroon. During the mid-1980s, the insect spread over much of central and northern Cameroon to Chad, Mali, Niger and Nigeria. In Nigeria, infestations have been treated with chemicals and infested branches have been removed. An outbreak, which occurred in the Lake Chad Basin in 1987, is believed related to stress associated with lowering of the water table ( Pirani, 1994 ).

The large scale insect, Pulvinaria maxima [ Megapulvinaria maxima ] (Homoptera: Coccididae), occurs throughout the Indian subcontinent and Malaysia and epidemics have been recorded in central and southern India. Both adults and nymphs feed on the sap of tender shoots and leaves. A heavily infested tree in an advanced stage of attack is conspicuously coated with thick, sticky white patches. Heavy infestations reduce tree vigour and promote premature leaf fall and dieback of infested shoots. Repeated attacks can kill trees. The feeding scales produce honeydew, a sweet substance that serves as a medium for the growth of sooty moulds ( Carlowitz, 1991 ).

The lesser snow scale, Pinnaspis strachani (Homoptera: Diaspididae) has a wide distribution and host range. Colonies of this woolly scale attack shoots and foliage of A. indica in Africa, Asia and Latin America ( Boa, 1995 ).

An eriophyid mite, Calipitrimerus azadirachtae [ Calepitrimerus azadirachtae ], has been recorded on foliage and tender shoots of A. indica in India. Feeding causes yellowing of foliage, deformity and desiccation of foliage and shoots. In some cases, the damage caused can be severe ( Tewari, 1992 ; Pirani, 1994 ).

An unidentified mollusc has caused 15-20% seedling mortality in nurseries of A. indica in Mahsana and Gandhinagar, India. Feeding occurs on the tender stem above the root collar and results in girdling (Vietmeyer, 1992; Pirani, 1994 ).

In Nigeria, damage to A. indica by several species of mammals has been reported. Browsing by domestic goats, Capra hircus, damages plantings. The red flanked duiker, Cephalophus rufilatus, occasionally causes slight bark damage. The Nigerian hare, Lepus crawshayi [ Lepus victoriae ], is suspected of eating the tops of seedlings in forest nurseries (Hocking, 1993; Pirani, 1994 ).

The fruits, seeds, and foliage of A. indica contain several compounds that repel or kill insects, inhibit the growth and development of fungi, and limit the infective ability of plant viruses. Despite this, several herbivores have been recorded on A. indica ( Pirani, 1994 ; Siddiqui, 1995 ); however, relatively few cause serious damage ( Tewari, 1992 ). Eight orders and 32 families of insects have been recorded feeding on A. indica .

A number of foliage feeding insects have been reported, although they are not extensive or frequent defoliators of A. indica trees. Fire ants ( Solenopsis spp.) have caused severe defoliation of three- to six-year-old trees in Andhra Pradesh, India and A. indica was the only plant fed upon, even though other plants were available. In Central and South America, leaf cutting ants ( Acromyrmex spp.) are common defoliators. Loopers (Lepidoptera: Geometridae) have occasionally been reported as defoliators, as has the widely distributed species Ascotis selenaria . Boarmia variegata also defoliates A. indica in nurseries in India, and Lychnis coronaria is found both in nurseries and on young seedlings. Caterpillars of the genus Eucema (Lepidoptera: Pieridae) also have been reported as defoliators ( Pirani, 1994 ; Luna, 1996 ).

The powder post beetles Apate monachus and A. terebrans are native to most of Africa, having a wide range of host plants, including A. indica . The larvae feed on the sapwood of dead trees and logs, and reduce it to a fine powder. Adults attack young trees and bore into small stems and branches either killing trees directly or making them susceptible to mechanical injury. Both species have been introduced to the Caribbean Islands and Brazil ( Hocking, 1993 ; Pirani, 1994 ). In addition, two powder post stem borers identified as species of Amphicerus and Sinoxylon have been reported as infesting neem trees in Rajasthan ( Singh et al., 2024 ). Cydia ( Laspyresia ) aurantiana and C. koenigian are both shoot borers and foliage feeders, and boring can kill buds and cause excessive branching. In some cases, up to 55% of A. indica shoots have been infested by C. aurantiana ( Pillai and Gopi, 1990 ). Several species of termites have been reported, sometimes locally damaging but do not kill living trees.

Sucking insects constitute the largest group of insects that utilize A. indica as a host plant. At least 20 species representing nine families, have been recorded, feeding on the foliage, branches and stems of host plants. This causes desiccation of plant tissue and results in drying of the foliage, defoliation, stem and branch dieback, and occasional tree mortality ( Tewari, 1992 ; Gupta, 1993 ; Pirani, 1994 ). Some species have salivary toxins that accelerate damage and tree death. An insect known as the tea mosquito ( Helopeltis antonii ) attacks terminal shoots, causing a drying of the foliage and terminal shoots believed to be due to a phytotoxic reaction to the saliva of the feeding insects. While large trees tend to recover, heavy infestations have been shown to cause seedling mortality and widespread damage has been reported in southern India. H. antonii is also a pest of cashew ( Anacardium occidentale ) plantations, and it is believed that large numbers of insects are carried by northeast monsoons from cashew to A. indica plantations from October to December.

The Oriental yellow scale or cochineal ( Aonidiella orientalis ) has caused widespread damage in parts of Africa and India, attacking the foliage and young stems and heavy feeding gives trees a burnt appearance. A. orientalis has a wide distribution and has been reported in China, Southeast Asia, Australia, the Indian subcontinent, Iran, the Arabian Peninsula, USA (Florida) and the Caribbean, found primarily on citrus and other tropical fruit trees. A. orientalis was reported on A. indica in Sudan in 1935, and in Cameroon in 1972, and during the mid-1980s, it spread over much of central and northern Cameroon to Chad, Mali, Niger and Nigeria. In Nigeria, infestations have been treated with pesticides and infested branches have been removed. An outbreak which occurred in the Lake Chad Basin in 1987 is believed to be related to stress associated with lowering of the water table ( Pirani, 1994 ). The large scale insect, Pulvinaria maxima [ Megapulvinaria maxima ] (Homoptera: Coccididae), occurs throughout the Indian subcontinent and Malaysia and epidemics have been recorded in central and southern India. Both adults and nymphs feed on the sap of tender shoots and leaves and heavily infested trees in an advanced stage of attack are conspicuously coated with thick, sticky white patches. Heavy infestations reduce tree vigour and promote premature leaf fall and dieback of infested shoots and repeated attacks can kill trees. The feeding scales produce honeydew, a sweet substance that serves as a medium for the growth of sooty moulds ( Carlowitz, 1991 ). The lesser snow scale ( Pinnaspis strachani ) has a wide distribution and host range and colonies of this woolly scale attack shoots and foliage of A. indica in Africa, Asia and Latin America.

An eriophyid mite ( Calipitrimerus azadirachtae [ Calepitrimerus azadirachtae ]) has been recorded on foliage and tender shoots of A. indica in India. Feeding causes yellowing of foliage, deformity, and desiccation of foliage and shoots and, in some cases, the damage caused can be severe ( Tewari, 1992 ; Pirani, 1994 ).

In South and Southeast Asia, minor damage is caused by torticid moths ( Adoxophyes spp.). Stored neem kernels have reportedly been damaged by Oryzaephilus larvae in India, and by Carpophilus dimidiatus in Ecuador ( PROTA, 2024 ).

The fungus Oidium azadirachtae causes a powdery mildew of neem foliage and several bacteria, including Pseudomonas viticola [ Xanthomonas campestris pv. viticola ], P. azadirachtae [ Xanthomonas campestris pv. azadirachtae ] and Xanthomonas azadirachtin, cause leaf spot diseases ( Tewari, 1992 ). In India, the bacterium Pseudomonas azadirachtae [ Xanthomonas campestris pv. azadirachtae ] may damage leaves ( PROTA, 2024 ). Root rot is caused by the fungus Ganoderma lucidum, with a worldwide distribution and a broad host range. Sporadic infections occur in young plantings of A. indica when stumps and roots of the previous tree crop are not removed from the site, and it attacks the sapwood and causes a white spongy rot. Symptoms of infection are pale, thin foliage and branch dieback, and fruiting bodies often occur at the base of the stem (Vietmeyer, 1992; Pirani, 1994 ). A. indica is one of many plants affected by pink disease caused by the fungus Corticium salmonicolor [ Phanerochaete salmonicolor ]. This disease can cause serious damage, especially under tropical conditions ( Hocking, 1993 ). The earliest sign of infection is the presence of white or pink pustules on dead bark, and a conspicuous pink layer of fungus mycelium spreads over the bark. In time, the bark may be entirely destroyed and the outer layers of wood killed, and branches are killed quickly causing the foliage to wilt and turn black.

In India and elsewhere , Pseudocercospora subsessilis is the most common fungus attacking the leaves of neem, causing a shothole effect ( PROTA, 2024 ).

Azadirachta indica is one of many hosts of the mistletoe Dendrophthoe falcata, which is widely distributed in the Indian subcontinent and the Solomon Islands. A mistletoe of the genus Tapinanthus also infests A. indica and other trees in Nigeria ( Pirani, 1994 ; Luna, 1996 ) and is capable of killing branches and causing deformity.

Neem die-back disease is caused by the fungus Phomopsis azadirachtae in South India leading to symptoms including branch drying and premature fruit wilting, in turn leading to tree mortality ( Kurakula et al., 2023 ; Sidharthan and Kumar, 2024 ).

In Ghana, A. indica has interfered with agriculture as it rapidly establishes in fallowed fields and makes land unavailable for farming ( Chamberlain, 2000 ).

Azadirachta indica is invading natural areas in the Middle East, Brazil, Dominican Republic, northern Australia and much of sub-Saharan Africa ( Kairo et al., 2003 ; Freire et al., 2013 ; PROTA, 2014 ). Large infestations have also been observed in Ghana and elsewhere in West Africa. It is also invasive along the south coast of Kenya and is naturalized in parts of Ethiopia. This species is drought resistant and thrives in sub-arid to sub-humid areas and has become a serious weed in northern Australia where its seeds are spread down by watercourses and by fruit-eating birds.

Azadirachta indica colonization is a threat to endemic coastal forests in Kenya (Hamilton A, World Wide Fund for Nature, Godalming, UK, personal communication, 2002) and to endangered dry coastal forest in Ghana where it is of particular concern in relation to rare trees such as Talbotiella gentii ( Chamberlain, 2000 ). Chamberlain (2000) reports the hypothesis that reduction in mammalian abundance and biodiversity in the Accra Plains, Ghana may have occurred in response to A. indica invasion of savannah habitats and changes to natural forest successions. The Government of Australia (1998) cites concerns over the potential impacts on native insects, fish and amphibians. This species is invading and outcompeting native vegetation in dry, arid, semiarid ecosystems as well as in riparian zones and coastal bushlands in South America, Africa and the Caribbean ( Kairo et al., 2003 ; Freire et al., 2013 ; PROTA, 2014 ).

There is evidence that extracts from A. indica can affect certain freshwater wildlife including fish and tadpoles. It also negatively impacts upon biodiversity by excluding native species.

This drought-tolerant species is grown to prevent soil erosion and to help in soil conservation and improvement. A. indica is considered one of the most suitable multi-purpose hardy tree species for rehabilitation of medium and deep ravines of Chambal ravines in India ( Singh et al., 2020 ). Since it is drought resistant with a well-developed root system capable of extracting nutrients form the lower soil levels, it is suitable for dune-fixation. It is used in composting and manuring. Specifically, neem leaves and small twigs are used as green manure and mulch. Farmers in India use neem cake (the residue left after extracting oil from the seeds) as a soil amendment and organic manure. It is believed to enhance the efficiency of nitrogen fertilizers by reducing the rate of nitrification and inhibiting soil pests including fungi, nematodes and insects ( PROTA, 2024 ). The use of neem oil-coated urea with an optimum rate can be considered a viable option for appropriate nitrogen management in rice production ( Timilsina et al., 2023 ). Furthermore, neem oil coated prilled urea has been used successfully for the slow release of nitrogen by manipulated nitrogen transformation in the soil, and enhancing nitrogen efficiency ( Nawaz et al., 2021 ). Neem cake has been identified as a cost-effective nitrification inhibitor module for cauliflower under mid-hilly conditions ( Shubham et al., 2023 ). Neem cake has also been shown to produce superior results with respect to yield of bitter gourd ( Rai et al., 2023 ). In countries from Somalia to Mauritania, it is an important tree for helping to prevent the spread of the Sahara Desert (Vietmeyer, 1992). A. indica improves soil fertility and water holding capacity, and can neutralize acidic soils, and therefore, it is useful for wasteland reclamation ( Webb et al., 1984 ). It can be grown on saline and alkaline soils with pH of up to 9.8 and with a soluble salt content up to 0.45 % in the subsoil ( Singh, 1989 ). It is very suitable for growing along roadsides and canal banks. As A. indica is believed to discourage diseases and pests, it is widely planted on homesteads. Material from A. indica is reported to affect more than 200 insect species, as well as some mites, nematodes, fungi, bacteria and viruses. A. indica tends towards a deeply tap-rooted habit in suitable soils, and so competes very little with agricultural crops for scarce soil moisture, and crops such as sorghum grow well close to the trunk. Intercropping neem with pearl millet, Pennisetum glaucum, has yielded good results in India ( PROTA, 2024 ). A. indica plantations have also been raised by taungya methods ( Hocking, 1993 ). As a result of its large crown, it is often grown for shade and shelter. It is planted widely as an avenue tree in towns and villages and along roads in many tropical countries. 50,000 neem trees have been planted in the Arafath plane near Mecca in Saudi Arabia to provide shade to Muslim pilgrims. Owing to its low branching, neem is grown as a windbreak ( PROTA, 2024 ). A. indica could also be useful for remediating heavy metals in contaminated soil ( Aliyu et al., 2023 ). Research has shown that natural coagulants such as A. indica can be successfully used for the removal of turbidity and faecal bacteria from hospital wastewater ( Tometin et al., 2022 ). The application of neem seed biochar, either alone or in combination with poultry manure, to cucumber ( Cucumis sativus ) can serve as a sustainable means of producing crops in the tropics ( Effa et al., 2023 ).

Traditionally, A. indica is used by rural people for its medicinal properties. It has a long history of use dating back to the Vedic period of India (approximately 6000 years BP) ( Tewari, 1992 ).

Almost all parts of the tree are used as medicine including the leaves, stem, bark, fruits, seeds, branches, flowers, roots, sap, gum and wood ( MPNS, 2024 ). An overview of the medicinal importance of A. indica is provided by Devi and Sharma (2023) . In Ayurvedic medicine, the bark and leaves are used for skin diseases, flowers as a tonic and stomachic, and fruits as a purgative and emollient. Various types of organic compounds have been isolated from different parts of the tree. These organic compounds are widely used as medicines and pesticides. Biologically active, volatile organic sulphur compounds are liberated by crushing fresh seeds. As many as 25 volatile compounds have been identified with di-n-propyl-disulfide being the chief constituent. The most active anti-feedant in the seed is azadirachtin, found pure as a microcrystalline solid. Stem and root bark has astringent, tonic, anti-periodic and other medicinal properties. The bark, leaves and fruit are used in the treatment of infections and diseases. The bark is bitter, a tonic and an astringent, and has traditionally been used to treat fever, nausea, vomiting and skin diseases. The root bark is more effective in this case than the stem bark and young fruit ( Tewari, 1992 ).

Various parts of A. indica have anthelmintic, anti-periodic, antiseptic, diuretic and purgative actions, and are also used to treat pimples, boils, eye diseases, hepatitis, leprosy, rheumatism, scrofula, ringworm and ulcers ( PROTA, 2024 ). In a polyherbal gel, neem appears to be clinically effective in treating canker sores ( Sudha et al., 2024 ). A. indica is used in the treatment of acne vulgaris in India ( Biswas and Biswas, 2023 ). A. indica is one of the most frequently used indigenous medicinal plants in Africa for the management of diabetes ( Frimpong et al., 2024 ). Other research confirms that A. indica has an anti-diabetic action, and its aqueous extract is used to treat diabetes ( Sen et al., 2023 ; Prajapati et al., 2024 ). In terms of scalp and hair health, a combined extract of rosemary and neem formulated into hair gel and leave-in tonic demonstrated superior efficacy against Malassezia furfur (a causative agent of dandruff) and Trichophyton rubrum (associated with scalp disorders) compared to the conventional anti-fungal agent ketoconazole ( Hashem et al., 2024 ). Neem extract is a key ingredient in a pure herbal anti-dandruff shampoo that has been developed ( Alam et al., 2023 ). In addition, decoctions and infusions prepared from dried and fresh neem leaves show promising anti-dermatophytic activity against Microsporum canis and Trichophyton tonsurans, supporting the traditional use of neem trees to treat fungal infections ( Tauseef et al., 2024 ). A. indica has immunity-boosting, anti-viral, anti-bacterial, antioxidant and anti-inflammatory actions that can suppress and treat the symptoms of COVID-19 ( Afrid et al., 2023 ; Chandra et al., 2023 ; Kumar et al., 2023 ). The biomedical and anti-viral properties of A. indica extracts could be of importance in the design of potential anti-SARS-CoV-2 nanoformulations ( Foka et al., 2022 ). Research has confirmed that A. indica herbal extracts are able to control vaginal pathogens including Aeromonas cavia [ Aeromonas punctata ], Lactobacillus, Staphylococcus aureus and Klebsiella pneumoniae without any side-effects ( Varalakshmi et al., 2023 ). Nimbolide, a bioactive compound derived from A. indica, has demonstrated therapeutic potential for osteoarthritis, rheumatoid arthritis, cardiovascular, inflammation and cancer ( Rajendran et al., 2024 ). For example , A. indic a has shown potential therapeutic effect on non-small cell lung cancer ( Nath et al., 2023b ). A. indica is considered an important plant in the control of oral disease conditions; as it shows significant protease inhibition activity, the active ingredient could act as a potential anti-inflammatory agent and help to prevent or control oral disease conditions such as gingivitis and periodontitis ( Assiry et al., 2022 ; Pasupluleti et al., 2023 ). A. indica has been used as a key constituent of dental anti-microbial toothpaste ( Oluwasina et al., 2023 ). Phytochemical metabolites contained in the ethanolic extracts of neem leaves could contribute a promising agent in treating a biofilm-mediated root canal infection of Enterococcus faecalis ( Suhartono et al., 2023 ). Phytochemicals of neem seeds have strong anti-viral potential against hepatitis C virus without having any significant cytotoxic effects ( Hussain et al., 2023a ).

The leaves are an old and popular remedy for skin diseases. The fresh juice of the leaves is administered with salt to treat intestinal worms and with honey for skin diseases and jaundice. As an external application for skin diseases, the leaves are used in variety of forms (poultice, ointment and liniment). For example, they are used as a poultice for boils ( Flora of Pakistan Editorial Committee, 2024 ). A strong decoction of fresh leaves produces an antiseptic which may be used in place of a weak solution of carbolic acid. A hot infusion of the leaves is used for fomenting swollen glands, bruises and sprains, and appears to be an anodyne ( Siddiqui, 1995 ). Leaf teas are used to treat malaria ( Lau et al., 2024 ; Maafoh and Onyedibe, 2024 ). Furthermore, neem oil-based bilayer tablets can be used as an effective tool for the control of vector-borne diseases ( Swathy et al., 2023 ). A steam inhalation from five handfuls of boiled neem leaves relieves rheumatism ( PROTA, 2024 ). Neem leaf alcohol extract shows anti-fungal activity and can be useful against candidiasis brought on by Candida species ( Ridhorkar and Kushwah, 2024 ). Ethanolic leaf extracts of A. indica have shown good potential as anti-microbials against infections of methicillin-resistant Staphylococcus aureus ( Adeluola et al., 2023 ). The anti-microbial nature of A. indica makes it a good constituent of herbal handwash formulation for reducing the amount of bacteria on hands ( Irfan et al., 2023 ). The fruits act as a purgative and an emollient, and are useful in the control of intestinal worms, urinary tract diseases and piles. The dry seeds possess almost the same properties as the oil when brushed and mixed with water or other liquids.

The seed oil is the most important medicinal product of this species from a commercial point of view. It is antiseptic and has proved to be useful in treating skin diseases, ulcers, rheumatism and sprains. Oil extracted from the seeds can be used as an anthelmintic and a purgative ( Flora of Pakistan Editorial Committee, 2024 ). The oil saponifies readily and is used in the manufacture of a medicinal soap because of its antiseptic properties. This soap is very effective for washing sores and for general uses similar to those of carbolic soap. In India, more than 18,000 t of neem seed oil is used for soap making. Assuming a fruit yield of 25 kg per tree and an oil content of 10%, this oil must derive from about 7.2 million trees ( PROTA, 2024 ). The flowers are useful in some cases of atonic dyspepsia and general debility. There are reports that the toddy (fermented sap) of the tree is useful in the care of some chronic diseases.

Azadirachta indica is also used in veterinary medicine such as the treatment of nematode parasite infections such as Strongylus, Parascaris and Ascaris spp. in goats ( Shrivastava et al., 2023 ). Neem leaves could potentially be a good supplement for goat feed, increasing growth performance and propionic acid and modulating the abundance of Butyrivibrio fibrisolvens and Streptococcus gallolyticus ( Taethaisong et al., 2023 ). Research also reveals that transdermal film of A. indica extract can be considered for the treatment of mastitis in the dairy industry ( Prabhu et al., 2024 ). A combination of garlic and neem was found to have better anthelmintic effects in comparison to chemical anthelmintics and might improve the production performance of dairy cows ( Adhana et al., 2023 ). Oil of A. indica can be used in an integrated tick management to reduce the tick burden on animals ( Shakya et al., 2024 ; Traore et al., 2024 ). Similarly, ethanol extracts from the leaves of A. indica can be used as bioacaricide ( Privat et al., 2023 ). In addition, the administration of neem oil to control caprine pediculosis caused by sucking lice represents an alternative to synthetic compounds ( Cotticelli et al., 2023 ). Neem extract functions as anti-coccidial medication that can enhance broiler chicks’ immune state ( Kairy et al., 2024 ). Dietary supplementation of neem leaves powder (2 g/kg) has the potential to improve the growth performance of broiler chickens ( Nath et al., 2023a ). Methanolic neem leaf extract possesses potential antioxidants with the power to control Newcastle disease virus shedding and infection in broilers and could be a source for new alternative anti-virals ( Akhtar et al., 2023 ; El-Basuni et al., 2023 ). A combination of neem leaves extracts 8% and chicken infectious anaemia vaccination is a potent anti-viral and has immunostimulant properties during the production cycle of broilers ( Hegazy et al., 2023 ). Moringa and neem leaf meal in combined form (5%+1%) have a significant potential to modulate haematological profile, immunity and gut microflora in Japanese quails ( Chachar et al., 2024 ). Neem aqueous extract holds potential as a natural and effective treatment option for Enterocytozoon hepatopenaei infection in shrimp, with significant implications in the aquaculture sector ( Madesh et al., 2023 ). Dietary A. indica seed protein hydrolysate inclusion has been shown to enhance the growth rate, economic efficiency, health status and resistance of Nile tilapia to the challenge of Streptococcus agalactiae ( Rahman et al., 2023a ). Neem seed protein hydrolysate can substitute 40% of the dietary fishmeal protein in Nile tilapia while promoting the fish’s immune competence, growth rate, digestive and adsorptive capability, and disease resistance ( Rahman et al., 2023b ).

Synthetic pesticides have caused a resurgence of pest resistance and secondary pest outbreaks. The environmental degradation due to excessive use of pesticides has also renewed interest all over the world in natural pesticides for ecological sustainability ( Sundararaj et al., 1995 ). A. indica provides natural pesticides. As a poison, azadirachtin has been identified as A. indica ’s principal active compound. Extracts can be made from the leaves and other tissues, but the seeds contain the highest concentrations of the compound. In India, some neem-based pesticides include Fortune Azadi, Azadi, Godrej Achook, Margocide, Neemarin, Nimbecidine and Repelin. Acting as an insect repellent, neem inhibits feeding, and disrupts insect growth, metamorphosis and reproduction. Formulations based on A. indica do not usually kill insects directly but alter their behaviour in significant ways to reduce pest damage to crops and reduce their reproductive potential. Azadirachtin affects insect physiology by mimicking a natural hormone. It has been shown to affect egg production and hatching rates, and can inhibit moulting, preventing larvae from developing into pupae. Many foliage-feeding species avoid plants treated with neem compounds or cease eating after ingesting them. It has proven effective as an anti-feedant on about 100 insect species ( PROTA, 2024 ). Azadirachtin exhibited relatively high toxicity on red imported fire ants ( Solenopsis invicta ) and is therefore likely to have a highly prominent potential in the management of S. invicta ( Liang et al., 2023 ). Similarly, azadirachtin has been shown to efficiently control one of the most important pests of maize in Hungary, the western corn rootworm ( Diabrotica virgifera virgifera ) in its larval stage ( Levente and Rita, 2023 ).

In a farm trial in Sind, Pakistan, extracts prepared from A. indica seed had a controlling effect on more than 80% of the major insect pests in stored grain, reducing grain damage for up to 6 months and remaining effective for up to 13 months ( Siddiqui, 1995 ). Techniques have been developed to prepare a ready-to-use pest control material known as neem seed bitters. It is produced by soaking powdered neem seed kernels in water for 12-16 h at room temperature. The filtrate is then freeze-dried, yielding a yellowish-brown crystalline material which is readily soluble in water. Application of seed bitters in field trials on rice and cotton in Pakistan has successfully controlled pests. This biopesticide is environmentally safe and cheap ( Siddiqui, 1995 ).

Extracts work well to protect plants from defoliation without affecting beneficial pollinating insects like honeybees. Tests of neem extracts have shown results on about 300 insect species, mostly in orders Coleoptera (weevils and beetles); Dictyoptera (mantids and cockroaches); Diptera (flies); Heteroptera (true bugs); Homoptera (aphids, wasps, leaf hoppers and ants); Isoptera (termites); Lepidoptera (butterflies and moths); Orthoptera (katydids, grasshoppers); Siphonaptera (fleas); and Thysanoptera (thrips). Crudely produced neem extracts can also provide excellent control on beetle larvae and caterpillars. Traditionally, ‘neem tea’ is produced. The seeds are dried, crushed and soaked in water overnight to produce a liquid pesticide that can be applied directly to crops. Crushed seed kernels may also be used as a dry pesticide application, especially to control stem borers on young plants. Neem is also being used in mosquito-repellent coils ( PROTA, 2024 ).

There is a wealth of studies that confirm the efficacy of neem as a biopesticide. Neem seed kernel extract at 10% has been found to be effective in reducing the growth of Exserohilum turcicum [ Setosphaeria turcica ] which causes leaf blight in maize ( Kumar et al., 2024 ). A. indica is one of the species used as a botanical pesticide against the fall armyworm Spodoptera frugiperda affecting maize production in the Central region of Burkina Faso ( Salo et al., 2024 ). Research in Nigeria also showed that neem leaf treatments reduced the severity of plant damage caused by fall armyworm ( Ewansiha et al., 2023 ). Neem oil as an insect growth regulator has exhibited inhibitory properties against the growth and survival of the bagworm ( Metisa plana ) larvae, a major leaf-defoliating insect pest that causes severe damage and loss to oil palm crops notably in Peninsular Malaysia, resulting in a significant increase in mortality ( Ahmad et al., 2024 ). Neem seed powder was effective as a grain protectant against Callosobruchus chinensi s on green gram in storage ( Limma et al., 2024 ). Among botanicals tested, neem leaf powder proved the best in protecting chickpea from pulse beetle, C. chinensis in stored chickpea ( Mounika et al., 2022 ). Similarly, amongst botanical oils and leaf powder tested, castor oil 2% and neem leaf powder 1% achieved maximum adult mortality at 72 h after treatment of the lesser grain borer, Rhyzopertha dominica in stored wheat ( Syed et al., 2024 ). Neem has been found to effectively control Phthorimaea absoluta, a global constraint to tomato production that can cause up to 100% yield loss and could be integrated into Integrated Pest Management programmes ( Ochieng et al., 2024 ). A. indica expressed significant effect against brown leaf spot disease of rice caused by Bipolaris oryzae [ Cochliobolus miyabeanus ] ( Chhabra et al., 2023 ; Shaheen et al., 2024 ). Neem leaf extract possesses fungicidal properties against Lasiodiplodia theobromae, offering a natural alternative for controlling this pathogen and reducing pesticide residues in stored kola nuts ( Cola nitida ) ( Olahan and Ajadi, 2024 ). Among eco-friendly management practices for the management of aphids, neem formulation (3000 ppm) recorded the maximum seed yield and green fodder. Among all biorational products tested, neem oil provided the maximum protection against aphids in cumin crop as well as the maximum yield ( Kant et al., 2024 ). Neem aqueous extract has also been found to be effective for the management of aphids and aphid-borne virus in cowpea fields ( Karem et al., 2022 ). Neem has been suggested from experimental results for the management of mustard aphids, the most concerning pest of rapeseed in the warm and humid areas of Nepal ( Khanal et al., 2023 ). Over a six-month study period, neem oil led to a reduction of 95% in lettuce aphids, Nasonovia ribisnigri ( Zao et al., 2023 ). Extract of A. indica has been recommended for the biorational management of wheat aphid ( Schizaphis graminum ) (Hussain et al., 2023b). Among three plant oils evaluated, neem oil was found to be the most effective against the crawler stage of papaya mealybug, Paracoccus marginatus ( Bora et al., 2024 ). Extracts from A. indica were effective in controlling Fusarium oxysporum f.sp. lycopersici causing tomato wilt ( Mustafa et al., 2024 ). Further research has shown that A. indica seed extracts have potent anti-fungal activity and could be used as an alternative to control F. oxysporum ( Toka et al., 2023 ). Among phytoextracts tested, neem exhibited the highest anti-fungal activity in inhibiting the growth of Fusarium oxysporum f.sp. lini at 5, 15 and 30% concentrations and this is of potential use in controlling Fusarium wilts of linseed ( Singh et al., 2023 ). Neem oil is effective against the shoot and fruit borer ( Leucinodes orbonalis ), a major insect pest of the brinjal crop ( Saljoqi et al., 2023 ; Tayyab et al., 2024 ). Neem oil showed high reduction of Penicillium sp., a major mould affecting the yield of oyster mushroom ( Khan et al., 2024 ). A. indica can be used to sustainably manage wet bubble disease ( Mycogone perniciosa [ Hypomyces perniciosus ]) in button mushroom ( Agaricus bisporus ) ( Kakraliya and Paswal, 2024 ). Neem seed kernel extract at 5% recorded the lowest damage (9.80%) by the serpentine leaf miner, Liriomyza trifolii in tomato among nine botanical insecticides tested ( Pathan et al., 2023 ). Formulated alcoholic extract of neem seed can act as an alternative to chemical fungicides to help control anthracnose and grey mould in strawberries ( Motallebi and Negahban, 2024 ). The addition of neem cake as a soil amendment can aid in developing a treatment strategy for the management of rhizome rot and wilt disease complex of ginger ( Sharma et al., 2024 ). Neem oil provided good biocontrol of root-knot nematode and also enhanced vegetative growth and nodulation in mungbean ( Vigna radiata ) ( Waghmare et al., 2024 ). Field trials have shown that seed yields of common bean ( Phaseolus vulgaris ) were approximately 350 kg/ha higher in bean plants treated with A. indica and Lippia javanica at 10% w/v compared to the negative control of untreated plants, suggesting that these botanical extracts could provide dual purpose pest and disease management for anthracnose caused by Colletotrichum spp. and crop pest insects ( Kushaha et al., 2024 ). Of all botanical extracts tested, A. indica was found to be the most effective against Hellula undalis infesting cabbage leading to the maximum yield of marketed heads ( Bharodiya and Jena, 2024 ). Neem leaf extracts display potential as an effective botanical insecticide against the pulse beetle infesting green gram ( Mahuri et al., 2024 ). The use of nanoemulsions with neem oil can be used in the control of post-harvest deterioration caused by Aspergillus niger in fruits ( Hernández-Becerra et al., 2023 ). Of various aqueous plant extracts tested, A. indica exhibited the highest mean repellency (up to 100%) in the store grain pest, Tribolium castaneum ( Ahmad et al., 2023 ). The use of neem seed kernel powder is an effective measure for controlling rice weevil Sitophilus oryzae while preserving the vitality and activity of the seeds as much as possible ( Mohammad et al., 2023 ). In a study of the efficacy of various eco-friendly pesticides on the insect pest complex of chilli ( Capsicum annuum ), the most effective control was recorded in neem oil against aphids, whitefly, thrips and fruit borer ( Wangpon et al., 2023 ). Among treatments examined, neem extract and cow urine led to the highest reduction in whitefly ( Bemisia tabaci ) population infesting aubergine ( Solanum melongena ) ( Abubakar et al., 2023 ). Amendment of 2.5% neem cake in the casing soil has been recommended for application in white button mushroom Agaricus bisporus production to control mushroom fly Lycoriella ingenua and symptoms of green mould disease ( Drobnjaković et al., 2023 ). Research demonstrates the pesticidal potential of neem extracts against the Acrida exaltata grasshopper species, with toxic impact on haematological, physiological and morphological behaviour ( Dutta and Dey, 2023 ). Neem oil, neem seed powder and neem leaf powder were considered among the best treatments for the management of angoumois grain moth ( Sitotroga cerealella ) of rice ( Roy et al., 2023 ). A. indica has been found to be useful in the management of Callosbruchus maculatus and shows potential in the production of new biopesticides for the control of stored grains pests ( Akbar et al., 2022 ). Amongst a variety of botanicals tested, aqueous extract of A. indica was the most efficient for reducing mycelial growth of Microdochium oryzae [ Monographella albescens ], the fungus causing leaf scald disease in rice ( Murudkar et al., 2023 ). Admixing neem oil and palm kernel oil has the potential insecticidal efficacy of controlling the bean weevil of stored cowpea and depending on the quantity of palm kernel oil mixed with neem oil, the seeds treated tend to have varying levels of bitterness and sulfurous odour deposit ( Giever and Echezona, 2023 ). Of a number of botanicals tested, neem oil was found to be the most effective as grain protectant against Caryedon serratus in stored groundnut ( Reddy et al., 2023 ). Neem leaf extract has been shown to be effective against white stem borer of rice ( Rahimoon et al., 2023 ). Neem oil (1.5%) + 0.2% isopropyl alcohol and neem oil (1.5%) + paraffin oil has been shown to significantly control papaya mealybug, Paracoccus marginatus ( Mwanauta et al., 2023 ). It has been recommended to use neem as an alternative method of termite control in integrated pest management of sugarcane ( Ghaffar et al., 2023 ). Neem leaf extract was found to be an anti-fungal agent and, when sprayed on grape berries, reduced decay of the fruits ( Nagaraju and Manoharachary, 2023 ). The incorporation of A. indica in soil as an organic amendment can work very well as a nematicide and can be successfully used for controlling root-knot nematodes replacing chemical treatments in order to avoid environmental pollution ( Saeed et al., 2021 ). Neem oil and neem seed kernel extract were found to be effective in reducing thrips population up to the extent of 41.01 and 4.14%, respectively, in 1 day after spraying in fully opened rose flower ( Elumalai et al., 2023 ). Of different plant extracts tested, in vitro results showed maximum mycelial growth inhibition of 45.80% in Trichoderma harzianum (which causes green mould of oyster mushrooms) using neem leaf extract at 10% concentration ( Jha et al., 2023 ). There is evidence that neem leaf extract has anti-fungal activity against Sclerotium rolfsii [ Athelia rolfsii ] and could be used as a potential alternative to synthetic fungicides for controlling damping-off disease in groundnut ( Masnilah et al., 2023 ). Neem oil could be used as an alternative control method in integrated pest management programmes against tomato fruitworm, Helicoverpa armigera and tobacco whitefly, Bemisia tabaci in tomato production in Benin ( Azandémè-Hounmalon et al., 2022 ). Neem oil reduced oviposition, nymph and adult emergence of B. tabaci by 50%, 70% and 80%, respectively, in a screenhouse experiment ( Amour et al., 2023 ). The evaluation of the bio-efficacy of various plant oils against the angoumois grain moth, S. cerealella in stored wheat showed that A. indica oil at 7.5 ml/kg was the most effective in controlling the S. cerealella ( Jena et al., 2023 ). Cowpea seeds treated with neem, covered with black muslin, and exposed to 72-hour of solar radiation were effective in controlling C. maculatus, a major field-to-store insect pest of stored cowpea in the tropics ( Akuba et al., 2023 ). The active ingredient azadirachtin can effectively control the western corn rootworm (Diabrotica virgifera virgifera ) pest of maize in its larval stage ( Vörös and Ledóné, 2023 ). With regard to the management of melon fruit fly ( Zeugodacus cucurbitae [ Bactrocera cucurbitae ]), neem leaf extracts perform best with regards to all parameters, reducing adult fruit fly population by 64% over the control ( Gosai and Adhikari, 2022 ). The combined application of Spinosad and A. indica extract is recommended to vegetable growers for effective integrated management of hadda beetle ( Epilachna vigintioctopunctata ) and other foliage-feeding beetles ( Hanif et al., 2021 ). Use of A. indica significantly reduces Hypsipyla grandella attack on Swietenia macrophylla plants planted in agroforestry systems ( Guerra-Arévalo et al., 2022 ).

Leaves are used as fodder, mulch and green manure ( Streets, 1962 ; Webb et al., 1984 ; Venkatesh et al., 2024 ), noted as a good fodder for goats and camels. The fodder contains 12-18% crude protein, 11-23% crude fibre, 8-19% total ash, 1-2% calcium, 0.2-0.4% phosphorus, 7-9% dichlorophosphate (DCP) and 50-55% TDN (total digestible nutrients). Dried leaves serve in place of mothballs ( Flora of Pakistan Editorial Committee, 2024 ). Leaves also provide protection for stored agricultural products such as grain pest control. Indo-Pakistani farmers mix 2-5 kg dried neem leaves/100 kg grain, or they soak empty sacks overnight in water containing 2-10 kg neem leaves/100 L water then dry these sacks before filling them with grain. Some farmers mix ground neem leaf paste with mud for making earthen containers for grain storage. Leaves are also used to protect vegetables in the store, e.g. cacao beans, pulses and fruit on market stalls in Indonesia is wrapped in fresh leaves to ward off insects. Laid between paper in books, leaves confer protection against bookworm. In the Gambia, a leaf pulp is used like soap to rid the head of lice ( PROTA, 2024 ). The leaves are also used as a pot-herb and are mixed with other vegetables in the preparation of soups and curries, imparting a slightly aromatic and bitter taste ( Lemmens et al., 1995 ). They are used as a ceremonial food in India where in early March, on Gudhi Padwa festival, which falls on the first day of Chaitra (the first day of the Hindu calendar), they are eaten first thing in the morning after cleaning one’s teeth and worshipping the sun. In Thailand, neem leaves are cooked and eaten with rice. Owing to neem’s bitter taste, many people eat a ‘chutney’ of neem leaves ground with jaggery (unrefined sugar) in order to purify the blood. Veterinary usage is made of neem leaves in Kordofan on ulcers on cattle ( PROTA, 2024 ).

On steam distillation, fresh leaves yield an odorous viscous essential oil which is a mixture of tetrasulfides of C3, C5, C6 and C9 units. Eight saturated hydrocarbons and nine fatty acids have been isolated. Chemically interesting constituents of leaves include limonoids, the most important being nimbin and its derivatives, such as pyronimbic acid, nimbinene, 6-diacetylnimbinene, nimbandiol, nimocinol, nimbocinone, nimocinolide, nimbocinolide, nimbolide, etc. ( Tewari, 1992 ). The leaves contain 12.4-18.3% crude proteins, 11.4-23.1% crude fibre, 43.3-66.6% N-free extract, 2.3-6.2%, ether extract and 7.7-18.9% ash. An average tree (8 m tall) gives about 350 kg of dry leaves ( Luna, 1996 ).

Leaf extracts from A. indica have been used in the green synthesis of silver nanoparticles, nano-sized metallic particles widely used in various fields including pharmaceutical, medicine, food and agriculture ( Tak et al., 2023 ; Yoosuf et al., 2023 ; Buggana et al., 2024 ) . A. indica leaf aqueous extract-based silver nanoparticles have been shown to be non-toxic to germinating rice seeds, and completely cured rice bakanae, a devastating seed-borne disease caused by Fusarium species, under net-house conditions ( Jahan et al., 2024 ). Neem extract is also used in the manufacture of zinc oxide nanoparticles which have applications in the removal of contaminants ( Rajashekara et al., 2024 ). Nanoparticles derived from A. indica have the potential to counter lead acetate-induced reproductive toxicity ( Vatika et al., 2024 ).

Dried flowers are edible, and essential oils have also been isolated from flowers. Dried flowers contain beta-sistosterol and beta-D glucoside kaempferol, thiomyl alcohol, melicitrin, benzyl alcohol and benzyl acetate. The pollen contains tyrosine, arginine, methionine, phenylalanine, histidine, glutamic acid and aminocaprylic acid. The older trees exude a nutritive sap in which the most abundant amino acid is aspartic acid; glucose and arabinose are the major constituent sugars. Flowers are occasionally consumed as vegetables ( PROTA, 2024 ).

Stem and root bark have astringent, tonic, anti-periodic and other medicinal properties. The activity of root bark is greater than stem bark. Stem bark contains 12-16% tannin and 8-11% non-tannin polyphenolics. Three polysaccharides and 24 diterpenoids have been isolated from the bark. Other compounds isolated from the bark include nimbolicin, nimbinene and 6-deacetylnimbinene ( Siddiqui, 1995 ). The bitter bark is used in making gum ( Flora of Pakistan Editorial Committee, 2024 ). As a fuel, the bark has been used for fuelwood and charcoal ( PROTA, 2024 ).

Biologically active, volatile organic sulfur compounds are liberated by crushing fresh seeds. As many as 25 volatile compounds have been identified with di-n-propyl-disulfide being the chief constituent. Seed kernels yield 40-50% oil with a bitter taste and a disagreeable odour. The oil has a high tocopherol content. The taste and flavour of the crude oil is due to the presence of lipid associates ( Tewari, 1992 ; Gupta, 1993 ; Luna, 1996 ). The oil contains six fatty acids, and the purified oil is similar to any other fatty acid. Refined oil is stable and does not become rancid when stored. The most active anti-feedant principle in the seed is azadirachtin, whose content in the seed varies from 0.2 to 3.5 g/kg. Pure azadirachtin is found as a microcrystalline solid. Other compounds isolated are salanin, 1.3-diacetylvilasinin, 3-deacetylsalanin, salanol, derivatives of azadirachtin and more than 30 less important compounds. Neem seed is used to produce biodiesel ( Iyyapan et al., 2024 ). Kathirvel and Palanimuthu (2022) have assessed diesel engine performance, combustion and emission characteristics with supplementation of neem oil methyl ester. Powdered neem seeds can also be a potential substitute for conventional chemical coagulants for drinking water treatment ( Khan et al., 2023 ).

Twigs are harvested and used extensively as toothbrushes. Only fresh twigs 1.5 cm diameter and 10-15 cm length are used, especially for pyorrhoea ( Tewari, 1992 ). Dentists find twigs effective in preventing periodontal disease. Young twigs are occasionally consumed as vegetables. Finely polished neem twig is also inserted as an antiseptic into the holes of the ears of newly born children that have been pierced ( PROTA, 2024 ).

The bark exudes a clean, bright, amber-coloured gum which is collected in small tears and fragments. Medicinally, it is used as a stimulant. It is also used as an adhesive in silk dyeing ( Tewari, 1992 ; Vietmeyer, 1992). This high-protein material has potential as a food additive and is widely used in Southeast Asia as ‘neem glue’ ( PROTA, 2024 ). In addition, neem gum can be exploited as a unique source of micro-organisms for agricultural and biotechnological applications ( Saxena et al., 2023 ).

The bark yields fibre which is of little commercial value but is often used in rope making in rural areas ( Gupta, 1993 ).

(See also 'Medicine' section above) A fixed, acrid and bitter oil of deep yellow colour and strongly disagreeable odour is extracted from the seed by boiling or applying pressure. It has long been produced in Asia on an industrial scale for cosmetics, soaps, pharmaceuticals and other non-edible products ( Orwa et al., 2009 ). Approximately 60% of neem oil collected in India is used for manufacturing soap. Much of the oil in India goes to the preparation of hair lotions and toothpaste. It is now being tested for use in cosmetics such as nail polish. Neem oil also serves as a starting point for synthesizing olein, stearins, lubricants and waxes ( PROTA, 2024 ). Neem oil is used locally in rural areas especially in India for burning in lamps. The smoke is said to have an offensive smell ( Luna, 1996 ). Neem oil is a powerful spermicide and can therefore be used as an inexpensive birth control method. Sensal, a neem oil-based product is being marketed in India as an intravaginal contraceptive. While neem oil has been used traditionally as a topical treatment for skin symptoms in both humans and livestock, it should not be ingested orally ( Orwa et al., 2009 ). Neem oil is valued at about USD 700/t ( PROTA, 2024 ). Neem oil is utilized as a raw material for biodiesel ( Raj et al., 2022 ).

Fruits are eaten fresh or cooked, or prepared as a desert or lemonade-type drink. The fruit is also an important source of food for some wildlife, especially birds and bats, although they digest only the pulp, not the seed. Fruit pulp is a promising substrate for generating methane gas ( PROTA, 2024 ).

As a human food, neem is cooked and eaten as a vegetable in the Malay Peninsula ( USDA-ARS, 2024 ). The physical, biochemical and functional properties of neem seed protein isolate including the rich abundance of glutamic and aspartic amino acids, and legumins, high arginine/lysine ration, high solubility in acidic and alkaline conditions, and relatively high oil and water holding capacities make it a good protein source for food formulation and nutraceutical ( Acho et al., 2023 ). Coating of A. indica can be considered an effective treatment for fruits and vegetables to prevent post-harvest losses ( Rahangale and Wadhai, 2023 ).

Among all treatments tested, A. indica extract 2% came out the most effective treatment in improving corm sprouting parameters of gladiolus and is considered an environmentally sound and safe alternative to chemicals used in breaking the dormancy of gladiolus and expanding its limits of cultivation ( Sharma et al., 2023 ). Neem oil has been used to optimize the in vitro culture of an ancient pear tree cultivar ( Pyrus communis ) ( Regni et al., 2023 ).

The sapwood of A. indica is yellow to yellowish-grey, turning pale yellowish-brown on exposure to the air. The heartwood is reddish to reddish-brown, darkening on exposure. The heartwood of A. indica contains esters of beta-sitosterol and 24-methylenecycloartenol, beta-sitosterol-beta-D glucoside, 24(28)-diene-3-beta-ol, 4 alpha-methyl-5-alpha-ergosta-beta, 24(28)-diene-3-beta-ol and others. On destructive distillation, it yields charcoal (30%) and pyrolignetic acid (38%). The wood oil contains beta-sitosterol, cycloeucalenol and methylenecycloartenol (Vietmeyer, 1992).

The wood is somewhat lustrous, hard to very hard, usually heavy with an air-dried specific gravity of 0.72-0.83. The density of the wood is 720-930 kg/cubic m at 12% mc ( PROTA, 2024 ). It has interlocked grain, sometimes exhibiting ribbon-grain effect on the longitudinal surfaces, usually medium to somewhat coarse-textured, occasionally a little finer in texture when fast grown. A good pattern is noticeable in plain sawn boards due to parenchyma bands as well as small knots ( Tewari, 1992 ; Siddiqui, 1995 ). Its important strength properties are as follows: bending strength 804 kg/cm²; modulus of elasticity 1009 kg/cm²; maximum crushing stress 6680 kg/cm². The wood is hard and resistant to termites, borers and fungi. The timber is reported to work well with hard machine tools, showing excellent machining properties except for planing. As the wood is hard and heavy, sawing is difficult. Hand tool and boring trials have given 100% defect-free samples. Similarly, turning tests have given good results, yielding 80% defect free samples ( Gupta, 1993 ).The timber is reputed to be durable in use. The heartwood is difficult to impregnate with preservatives due to gummy deposits in the vessels and perforation plates. It is difficult to treat with CCB (2:2:1), and penetration with CCB and creosote is only 0.1 cm for the sides and 0.2 cm for the ends. The species is reported to season well, with little deformation during air drying. Its shrinkage coefficient is 22.02. It takes 5-7 days to kiln-dry 2.5-cm planks from a green state to 12% moisture content ( Siddiqui, 1995 ). A. indica wood peels well. On the basis of tests for glue adhesion, tensile, bending and compressive strength, and amenability to preservative treatment and fireproofing, A. indica is considered suitable for general purpose plywood, fire retardant plywood and plywood for blockboard. A. indica timber is used for making doors, windows, agricultural implements, carts, axles, yokes, packing cases, ornamental ceilings, fence posts, in ship and boat building, and in furniture such as wardrobes, bookcases and closets, for which its insect repelling properties are useful ( Tewari, 1992 ; PROTA, 2024 ). Although it has satisfactory strength, it is not a preferred timber for furniture manufacture as it has rough and interlocked grain which does not allow a good finish. However, in recent years, painted furniture made from A. indica wood has become fashionable ( Siddiqui, 1995 ). A. indica provides good fuelwood with a calorific value of 6943 kcal/kg. In Ghana, it has become the leading source of fuelwood for the densely populated Accra Plains (Vietmeyer, 1992). It also makes good charcoal with an energy value only slightly below that of coal ( PROTA, 2024 ). A. indica leaf and seed extracts with 2.00% concentration as a biopreservative has also been shown to minimize fungal growth on wood specimens of Toona ciliata ( Thakur et al., 2023 ). A study to evaluate the suitability of neem wood ash as a raw material in the production of ceramic bricks confirms that incorporating ash into a clay material reduces environmental problems and the total cost of raw materials ( Fadil-Djenabou et al., 2023 ).

Azadirachta indica seedlings are susceptible to fire whereas mature trees are able to withstand fires ( Stoney, 1997 ). No other control methods have been documented, though it is assumed that seedling removal, or cutting with a stump treatment would be effective in preventing regeneration.

Azadirachta indica is a light demander but it also tolerates fairly heavy shade during its early development. It can grow with other crops, but cannot compete with weeds and grasses. The tree is highly susceptible to frost damage in the seedling and sapling stages. It is drought-hardy but cannot withstand waterlogging, the taproot rotting when soil moisture is excessive ( Pirani, 1994 ). A. indica is seldom found growing gregariously. It regenerates naturally and is propagated mainly through seed. It also regenerates well by coppicing and pollarding, and can produce root suckers, especially in dry localities (Vietmeyer, 1992; Luna, 1996 ). Birds and bats play an important role in dispersal of its seed. The fruit ripening period coincides with the rainy season, and under natural conditions, the fruit falls on the ground and germinates within 15 days. It has been recorded that germination is enhanced by passage through the guts of baboons ( Mabberley, 1997 ). A. indica is frequently self-sown in gardens and the areas around mature trees are quickly colonized by a carpet of seedlings. It has the ability to establish itself under the protection of thorny bushes and to survive in dry poor soils, provided it is not subjected to frost ( Tewari, 1992 ).

Azadirachta indica is propagated primarily through seed. The seeds are recalcitrant and are shed at relatively high moisture content, hence are prone to dehydration and chilling injuries ( Mishra, 1995 ). They have a short viability of 3-4 weeks. Seeds stored at 4°C show a high germination percentage. Mature seeds germinate readily within a week, with a germination rate of 75-90% ( PROTA, 2024 ). To maintain viability of the seeds, the drupes must be cleaned properly by depulping, either manually or mechanically under a stream of water to provide stones. Drying stones in shade is the most appropriate method although drying in the sun, an oven or vacuum provides acceptable results more quickly. Stones give better germination rates than seeds ( Pukittayacamee et al., 1995 ).

Successful establishment of A. indica plantations is possible through stump planting, which is considered better than direct sowing for many sites. However, Tewari (1995) suggests that direct sowing is more successful and cheaper in degraded forest areas, provided that protection and shelter are available to the young seedlings. Stumps are generally prepared from two-year-old seedlings raised in seed beds by trimming the plants to retain a 22-cm root and a five-cm shoot. Stumps are prepared under shaded conditions and transported in wet gunny bags ( Troup and Joshi, 1981 ). Experiments have shown that stumps prepared from two-year-old plants give better survival and height growth than one-year-old rootstocks.

Although the most popular and economic methods of propagation of A. indica in India are through direct sowing, transplanting seedlings in plastic containers and by stumps, it can also regenerate from root suckers and stem cuttings. It has been reported that application of indole-3-butyric acid and indole-3-acetic acid (500-1000 ppm) induced rooting in stem cuttings. Air-layering can also be done with the application of indole-3-butyric acid or naphthalene-1-acetic acid ( Pirani, 1994 ). Early fruiting can be induced without losing any economic value from the mother trees. Neem can also be propagated vegetatively by grafting, marcotting and tissue culture ( PROTA, 2024 ).

Direct sowing can be successfully carried out by dibbling, broadcast sowing and sowing in lines on mounds or ridges, in trenches, sunken beds or circular saucers, depending on site conditions. A. indica seed may be successfully dibbled under Euphorbia bushes. Small pits are made and three to five seeds are sown in each pit and covered with soil, sand or a mixture of sand and soil ( Troup and Joshi, 1981 ). Broadcast sowing may be carried out on ploughed or unploughed land. Very good results are obtained by ploughing up the ground twice. Experiments have shown that early ploughing during pre-monsoon showers gives significantly better results than ploughing once the monsoon has set in. In arid areas of the Indian sub-continent, ploughing should be done in early spring when the soil is still moist after winter rains ( Pirani, 1994 ). Line sowing has also been successful. After clear felling and grubbing out the stumps, the area is cultivated for 2 years with field crops. In the third year, the seed is sown in lines 4.5-5.5 m apart; smaller intervals have proved too close to suit the field crops, usually cotton, sesamum and arhar ( Cajanus cajan ).

Cultivation is continued in the fourth and fifth years, and blanks in the lines are filled in by further sowing. It may be extended by 2 years in exceptional cases if the lines have not been adequately stocked with seedlings. In some areas, sowing in lines 3 m apart on tilled soil has given good results ( Troup and Joshi, 1981 ; Pirani, 1994 ). Sowing of A. indica seed on mounds or ridges is prescribed for heavy soils. Sowing on mounds (about 70 cm high, 60 cm diameter at the top and 2 m diameter at the base) has yielded satisfactory results under poor soil conditions. On black cotton soil, sowing on mounds (3.7 m x 1.2 m x 46 cm) in rows 2.7 m apart has proved successful, with A. indica plants attaining a maximum height of 1.4 m 1 year after sowing ( Luna, 1996 ). Entire/polypot seedlings with a height of 20-25 cm by the beginning of the rainy season can be planted out in pits at a spacing of 3 x 3 m. Other spacings can be used depending on the purpose of planting. Trimming of leaves (except at the tip) and roots is desirable and has proved to be successful. Plants 25 cm tall are used for planting in arid areas; smaller plants are unable to bear the stress of the drought period ( Siddiqui, 1995 ). Strips in A. indica plantations are hoed (with very little breaking of the soil) to rid them of weeds and grass, leading to good health and survival of A. indica . The response appears to be due to eradication of the grass and weeds, and not from soil working ( Siddiqui, 1995 ). Loosening the soil to prevent caking and to promote soil aeration is not beneficial.

Weeding of neem plantations in dry areas is essential, as it cannot withstand competition, especially from grasses ( PROTA, 2024 ). Two weeding are usually sufficient in the first year. The first weeding should be carried out soon after germination is complete, and the second a month later. A third weeding may sometimes be required. In the second year, only one weeding is necessary. Ordinarily, first mechanical spacing is done when the crops attain the age of 3-4 years with direct sowing, and 5 years for transplanted seedlings. The silvicultural system under which A. indica is worked is either simple coppice or clear felling and re-planting. Roadside and avenue plantations are worked under a clear felling system. In felled coupes, regeneration occurs through coppice and root suckers as well as from natural regeneration from seedlings ( Siddiqui, 1995 ). Watering is necessary during the hot season, regularly but without excess, and especially during summer. Fertilizer may be needed during growth, regularly but with spacing. Neem responds well to chemical and organic fertilizers ( PROTA, 2024 ).

Azadirachta indica coppices freely, and early growth from coppice is faster than growth from seedlings. Whilst A. indica withstands pollarding well, seed production is adversely affected when trees are lopped for fodder ( Orwa et al., 2009 ).

The following information is based on experience in India, unless otherwise specified. Under dry conditions without artificial irrigation, A. indica has been seen to attain a height of 4 m in 5 years and 10 m in 25 years. Mean annual increment of the species has been recorded as 2.3-3.0 cubic m per hectare. However, annual growth rates of more than 20 cubic metres per hectare have also been recorded in Uganda and Nigeria (Vietmeyer, 1992). Sheikh (1993) and Webb et al. (1984) have reported annual growth rates of 5-18 cubic m per hectare for an eight-year-old plantation. The best economic rotation for wood production is considered to be 23 years ( Luna, 1996 ). The financial benefits of using A. indica products for controlling pests on agricultural crops are very high, with a benefit/cost ratio between 5:1 and 44:1 ( Kumar et al., 1995 ), i.e. the benefits obtained through protecting agricultural crops from harmful pests are much greater than the costs incurred using pest control products derived from A. indica . Mature trees produce 30-40 kg of fruit annually, which fall to the ground on ripening ( PROTA, 2024 ).

Two chromosome numbers have been recorded for this species, i.e. 2n=30 in root tip mitosis and 2n=28 ( Tewari, 1992 ). The genetic potential of A. indica has not been fully assessed. A marked difference in the yield of azadirachtin has been observed from different seed sources ( Siddiqui, 1995 ). Seed from Ghana gave 3.5 g/kg whereas Indian seed gave 0.2 g/kg. Therefore, genetic improvement studies should be undertaken to utilize the genetic variation in the species. The work should also include selection of A. indica plus trees for important traits, general growth, medicinal, insecticidal, anti-feedant and pesticidal characteristics, maturity and yield of fruits, and properties and yield of oil. Provenance studies should also be carried out to determine suitable seed sources for various localities. Here, care will have to be exercised because it is difficult to distinguish between natural stands and artificial plantations of this species. In many of the areas where A. indica has been introduced, unspecified Indian/Pakistani seed sources have been used. Therefore, provenance seed collection should be carried out in distinct populations of this species. An International Consultation on Establishment of Provenance Trials of this species was constituted by the FAO in 1993 to assist a number of countries to select suitable seed sources for planting. On the basis of results of progeny tests of plus trees and provenance studies, seed orchards could be established. Studies on mutation and polyploidy breeding, as well as tissue and vegetative propagation also need to be carried out as they hold great potential for genetic improvement of the species ( Tewari, 1992 ; Parveen et al., 1995 ). Fresh cotyledons have been found to be the best source of material for tissue culture ( PROTA, 2024 ). Germplasm collections are made, maintained, evaluated and distributed by Winrock International Institute for Agricultural Research in Bangkok, Thailand.

Phenotypically superior neem trees have been vegetatively propagated in India, Australia and Thailand. FAO and DANIDA have established provenance trials in Asia, South America and Africa. Various ecotypes of neem are thought to exist with variations in such characteristics as leaf palatability, root to above ground growth ratio and resistance to drought ( PROTA, 2024 ).

Azadirachta indica can only be grown only in localities which have a warm climate and do not experience frost. Further, under very dry conditions its growth and yield can be erratic and its susceptibility to pests is high ( Carlowitz, 1991 ; Vietmeyer, 1992). A lack of zinc or potassium in the soil reduces growth. A. indica seedlings are susceptible to fire. Large trees are prone to damage during hurricanes, cyclones and typhoons. The growth of the tree on farmland may possibly adversely affect crop productivity ( Singh, 1989 ). The short viability of the seed and different ripening times in various localities is a serious problem and poses logistic difficulties for the introduction of this species to new locations.

Much research is needed, such as on the plant’s agronomy, on methods of oil extraction, refining and deodorization, and on the use of the oil as a possible replacement for coconut or palm oils in manufacture. Further investigations of the insecticidal and anti-feedant compounds and of the therapeutic principles are also required ( PROTA, 2024 ).