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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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