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Horticulture

Neem The wonder tree

Most of the pesticides currently in use have caused serious social and environmental repercussions. Insecticides derived from plants are ecologically desirable and economically advantageous. More than 2,400 plant species possess pest control properties.

Early use of plants materials as pesticides
Scientists learned about the pest-control properties of plants by observing practice of traditional farming societies. The ancient Romans used false hellebore, veratrum album, as a rodenticide, and the Chinese are credited with discovering the insecticidal properties of Darns species, Pyrethrum was used as an insecticide in Persia, likewise tobacco plant preparations have been used for nearly two centuries. The nicotine-rich water has often been applied to plants in the Middle East as a crop protection measure. Nigerians have been using neem leaves for the control of stored grain pests.


Among 267 plant species used for pest control in China, aqueous extracts of Tripterygium wilfordii are sprayed to control caterpillars, tussock and pine moths, and mustard, melon, and rice leaf beetles; powdered roots of Stellera  chcmaejasme are mixed with top soil to control soil pests; and dried leaves of Melia azadarach are placed between the mat and supporting board of beds to control lice and fleas.

In the Indo-Pakistan sub-continent some of the medicinal planes namely 'Sweetflag' Acorns calamus "Kuth" Skimmia laureola " Mushkbala" valariana officianalis and "Ner" Skimmia laureola are frequently used in the northern hilly areas as insect deterrents. Articles placed in baskets of sandalwood, Santulum album, are immune to insects. Dried leaves of fenugreek, Trigonella foenum-graecum, are mixed with stored grains as insect repellent, especially during the rainy season. It is a common practice in India and Pakistan to apply turmeric powder, Curcuma longa, to stored "Basmati" rice for protection against the attack of insects.

Neem (Azyadirachta indica) has been the most traditionally used plant in the Indo-
Pakistan sub-continent and Africa. In Pakistan, fresh neem leaves are mixed with grains or these arc rubbed against the inside walls of mud bins. Sometimes the water extract is applied to [he gunny bags in which grains are to be stored. In India, dried neem leaves are spread in 5- 7 inch thick layer in grains.

Neem, the 'Wonder Tree'
Neem is very widely distributed on the globe, especially in the Asian, Middle East and African countries. It is known  as neeb in Arabic, neem in Hindi and Urdu, azad dirakht in Persian, and nimba in Sansikrit. It is a fast growing tree which can be established without irrigation in hot and dry regions of the world. It is native to Indo-Pakistan sub-continent. In South Asia, it is also found in Bangladesh, Upper Burma and in the drier parts of Sri Lanka. In Southeast Asia, it occurs scattered in Thailand, Southern Malaysia and in the drier Indonesian islands of Java. It is also found in the northern plains of Yemen and has been recently introduced into Saudi Arabia. In Africa, it is particularly widespread in Nigeria.

Neem - the wonder tree - has the potential of providing the best source of selective and environmentally acceptable biopesticdes. Various parts of the tree have a wide range of applications. In the pioneering work on the isolation of neem constituents in 1942, nimbin and nimhinin were first two crystalline compounds obtained from neem oil. Since then nearly 100 more constituents have been isolated from different parts of the tree and their structures elucidated. Among [hem liminoids have shown the greatest insect
growth-regulating activity- The work on the pesticidal activity of neem liminoid, later identified as Azadirachtin, opened up a new era of renewed research on neem as a source of biopesticies.

Neem products are unique, being not outright killers of pests. Instead, they alter an insect's behavior of life processing ways that can be extremely subtle. Eventually, the insect can no longer feed or breed or undergo metamorphosis and, hence, cannot cause Further damage.

Neem protects against storage pest
This is one of the oldest traditional use in Asia. For instance, treating jute sacks
with neem oil or neem extracts prevents pests, especially Sitophilus and Tribolium
species, from penetration into the bags  for several months. Neem oil is effective
and provides cheap protection against Stored grains pests, especially paddy, beans, cowpeas and other legumes- This process may be unsuited for large-scale
use, but it is useful for household use.

Neem has also been used in India to protect stored roots as well as tubers
against the potato moth..

Neem controls field crops pests
Neem products acts as antifeedant for grasshoppers, crickets, and locusts. A
number of species of these insects refuse to feed on neem-treated plants for several
days, sometimes several weeks. Neem oil causes "solitarization" of gregarious
locust nymphs. After exposure to doses equal to 2.5 liters per hectare, the juveniles
fail to form the massive, moving individuals. Although alive, they become solitary, lethargic, almost motionless and, thus, extremely susceptible to predators such as birds. Effect of neem on stored wheat insect infestation station is depicted in the following figure. The larvae of all beetles, especially those

EFFECT OF NEEM APPLICATION ON INSECT POPULATION IN STORED WHEAT
Insect counts per 500 gram wheat sample
 



of Phytophagous coccinellids (Colorado potato beetle and others), arc also sensitive to neem products. They refuse to feed on neem-treated plants, grow' slowly and some (such as soft-skinned larvae of the Colorado potato beetle) are killed on contact, from various field trials on moths, it appears that larvae of most lepidopterist pests are highly sensitive to neem.

In the Philippines, plots treated with neem cake had lower incidence of ragged stunt and tungro viruses. In field trials conducted in India, neem treatments were found effective against populations of green leafhopper, Nephotettix  virescens, yellow stem borer, Scirpophaga incertulas, rice gall midge, Orseolia oryzae and grasshoppers.

The American farmers spend more than USS 400 million annually to tight against
European corn borer. Laboratory tests using neem seed extracts, having 10 ppm
azadirachin, produced 100 per cent mortality. In the Dominican Republic, water extract of neem seed proved effective against Aphis gossypii on cucumber and okra and against Lipaphis erysimi on cabbage. Neem extracts are also effective against gyp5)" moth, horn flies, fruit flies and mosquitoes.

 Effects on vertebrates
Birds and fruit bats consume the sweet pulp of the neem fruit, bur not the seed. Birds given aqueous extract in diet looked sluggish soon after and some of them later died. Aqueous extract of young neem leaves fed to rats and rabbits showed a marked drop in blood glucose.

Concentration, Lambs refused to feed on dried neem leaves but fed well on leaves mixed with molasses. Goats in Senegal, consumed considerable amount of freshly depulped neem seeds (by fruit bats and birds) lying under the trees, without any ill effect. Buffaloes calves fed on neem seed cake mixed with molasses found it palatable. Extract from neem leaves, although very bitter, has been drunk as tea in India since time immemorial-

Beneficial insects are safe
Plant products, especially neem extracts, seem remarkably benign to spiders,
butterflies, and other insects, such as bees that pollinate crops and trees, ladybugs that consume aphids and wasps that act as parasites on various crop pests.

In general, this is because neem products must be ingested to be effective. Thus,
insects that feed on plant tissues succumb, while those that feed on nectar or other insects hardly accumulate significant concentrations of neem products.

What makes neem a pest repellant
One of the first active ingredients isolated from the neem, azadirachin has proved
to be the tree's main agent for battle against insects. It docs not kill insects immediately, instead it repels and disrupts their growth and reproduction. Neem
incapacitates the insects rather than killing them directly. Research over the last 20
years has shown that it is one of the most potent growth regulator and feeding
deterrent. Azadirtin is structurally similar to insect hormones called "ecdysones", which control the process of metamorphosis as the insects pass from larva to pupa to adult- On an average, neem kernels contain 0.2-0.4 per cent azadirachtin. In addition to this, meliantriol, salanin, nimbin, nimbidine and many other biologically active components have been reported in neem.

Farmers in Pakistan evince interest in neem products
During 1996, farmers established neem-based pesticide centers at five locations in Sindh province. Work on small scale production of neem-based pest control materials such as neem oil, neem cake etc- has expanded. Transfer of this technology in the Punjab province started in February 1999, Farmers have shown keen interest in the use of neem derivatives for pest control. FO


Dr. Gb«lam}il3ni is Director/'Prnciple Scieatific Officer, Integrated Pest Management Institute. National Agrcultural Research Center, Park Road. Islamabad.

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