Secrets of Neem Oil

When examining methods for pest control products, we must include Neem Oil. The Neem seeds and leaves contain many compounds that are useful for pest control. Unlike chemical insecticides, Neem compounds work on the insect’s hormonal system, not on the digestive or nervous system. Therefore, it does not lead to the development of resistance in future generations. These compounds belong to a general class of natural products called ‘limonoids.’

The limonoids present in neem make it a harmless and effective insecticide, pesticide, nematicide, fungicide, etc. The most significant limonoids found in neem with proven ability to block insect growth are Azadirachtin, Salannin, Meliantriol, and Nimbin. Azadirachtin is neem’s principal agent for controlling insects. ‘It appears to cause 90% of the effect on most pests. It does not kill insects – at least not immediately – instead, it both repels and disrupts their growth and reproduction. Over the past years, research has shown that it is the most potent growth regulator and feeding deterrent ever assayed. It will repel or reduce the feeding of many species of pest insects as well as some nematodes. It is so potent that a mere trace of its presence prevents some insects from even touching plants.’

Certain hormones are necessary for the growth and development of insects. These hormones control the process of metamorphosis as the insects pass from larva to pupa to adult. Azadirachtin blocks those parts of the insect’s brain that produce these vital hormones. As a result, insects are unable to molt. Through these subtle hormonal effects, this important compound of neem breaks the life cycle of insects. The insect populations drastically reduced as they become unable to reproduce.

Meliantriol and Salannin act as powerful antifeedants. Nimbin, as well as Nimbin (another neem component), have antiviral properties.

But, for all the uncertainty over details, various neem extracts are known to act on insects in the following ways:

• They are disrupting or inhibiting the development of eggs, larvae, or pupae.
• Blocking the molting of larvae or nymphs
• Disrupting mating and sexual communication
• Repelling larvae and adults
• Deterring females from laying eggs
• Sterilizing adults
• Poisoning larvae and adults
• Deterring feeding
• Blocking the ability to “swallow” (that is, reducing the motility of the gut)
• Sending metamorphosis awry at various stages
• Inhibits the formation of chitin

All these effects listed above are not equally strong. Blocking the larvae from molting is considered to be neem’s most important quality and used to eliminate many pest species. Neem products are harmless to most insect eaters, humans, and other mammals, except for specific marine life like crabs, lobsters, fishes, and tadpoles.

Despite high selectivity, neem derivatives affect 400 to 500 species of insects belonging to Blattodea, Caelifers, Dermaptera, Diptera, Ensifera, Heteroptera, Hymenoptera, Isoptera, Lepidoptera, Phasmida, Phthiraptera, Siphonaptera and Thysanoptera, one species of ostracod, several species of mites, and nematodes and even noxious snails and fungi, including aflatoxin-producing Aspergillus Flavus. Field trials in some major food crops in tropical countries will illustrate the value of neem-based pest management for enhancing agricultural productivity in Asia and Africa.

Neem’s effects on some major pests

Locusts (winged insects) are a great menace to crops and trees in Europe, Africa, and Asia are investigated in laboratory conditions, semi-field and field trials.

There was a powerful phagorepellent effect of Neem oil on the desert locust and the red locust.

Use Neem oil and related products against locusts and grasshopper species in farmer’s fields.

Neem oil enriched with azadirachtin prevents locusts from developing into their migratory swarms that are so destructive to vegetation. Even doses equal to a mere 2.5 liters per hectare are enough to avert locust plagues. “Although alive, they become solitary, lethargic, almost motionless and thus extremely susceptible to predators such as birds.”

Grasshopper nymphs are affected similarly by Neem Oil. Applying Neem products to soil or using seeds soaked with Neem products can protect some crops from locusts for a week to a month.

The neem seed extract retards the growth of several cockroach species. It kills the young cockroaches and inhibits the adults from laying eggs.

For Protecting Crops and Animals

Neem is quite effective against armyworm, one of the most devastating pests of food crops in the western hemisphere. Azadirachtin in low concentrations – a mere 10 mg per hectare – inhibits the insect pests.

Neem extract is useful against leaf miner, a severe pest in parts of North America. Neem seed extract works as well as available commercial synthetic pesticides. The US Environmental Protection Agency has approved it for use on leaf miners.

Experiments have shown that Neem products are quite effective against European corn borer, a deadly pest that causes massive damage to corn and other crops in Europe and North America.

Neem is beneficial as an anti-feeding and ovipositional repellent for protecting crops like tobacco, groundnut, cotton, and sweet potato from the damages caused by tobacco caterpillar or tobacco cutworm.

Neem products are quite effective against the larvae of many mosquito species that stop feeding and die after treatment. At present, developing countries use expensive imported pesticides to control the mosquito population. These countries can save a lot of money by using locally available simple Neem products equally effectively. Simple techniques such as throwing crushed Neem seeds into pools and ponds in the towns and villages can prevent mosquito breeding.

Experiments have shown that neem is also effective against fruit flies. Medfly, one of the most damaging horticulture pests, can be controlled by spraying neem solution under fruit trees. Neem has an advantage over the currently used pesticides. Whereas the conventional pesticides kill fruit flies and their internal parasites, neem products, on the other hand, leave the biological-control organisms unaffected; they only kill fruit flies. 

Neem is useful against the gypsy moth, a pest that is causing severe damage to forests in parts of North America. Laboratory tests have shown that a low concentration application of neem seed extract formulation, approved by the US Environmental protection Agency, can kill gypsy moths.

As mentioned above, neem products can influence about 400-500 insect species.

So far, we have concentrated on the effects of neem products on insects, which cause severe damage to crops and animals. As can be seen from the discussion above, neem and its products are highly effective against many pestiferous insects.

And Against Non-insect Pests Too

Research in recent years has shown that neem is quite effective against non-insect pests also.

Threadworms are among the most devastating agriculture pests. These nematodes are very difficult to control. The use of synthetic nematicides is not desirable as they cause toxicological effects. Research has shown that these pests are susceptible to neem products. ‘Certain limonoid fractions extracted from neem kernels are providing active protection/defense against root-knot nematodes.’ Water extracts of neem cake are also nematicidal.

Fungi attack plants and trees in numerous ways and forms. They cause massive damage to essential crops such as wheat, rice, and corn. Several tests have demonstrated that neem acts as a fungicide. Should this prove widely applicable, it would have enormously positive effects on agriculture, the environment, and food supply with special effects like reducing poverty, increasing production, etc., on a global scale.

Some tests have shown unusual and promising results Neem-leaf extracts failed to kill the fungus Aspergillus Flavus but completely stopped it from producing aflatoxin’. It is crucial because aflatoxin is a potent carcinogen causing increasing concern regarding the world’s food supplies.

As practiced today in most developing countries, Pest control relies mainly on the use of imported pesticides.  Although pesticides are generally profitable on a direct crop returns basis, their use often leads to the contamination of terrestrial and aquatic environments, damage to beneficial insects and wild biota, an accidental poisoning of humans and livestock, and the twin problems of pest resistance and resurgence.

More than 500 arthropod pest species have become resistant to one or more insecticides. Resistance of the cotton bollworm, Helicoverpa armigera, in India and Pakistan, and of the Colorado potato beetle, Leptinotarsa decemlineata, in the USA to all available insecticides, and resistance of the diamondback moth, Plutella xylostella, to all classes of insecticides, including Bacillus thuringiensis, in Hawaii, Malaysia, the Philippines, Taiwan, and Thailand, illustrate the complexity of the problem. Shifts in pest status-from minor to major, and pests’ resurgence, such as whiteflies, caused by direct or indirect destruction of pests natural enemies are other unwelcome developments associated with pesticide use.

A World Health Organization and United Nations Environmental Program report (WHO/UNEP 1989) estimated there are 1 million human pesticide poisoning cases each year globally, with about 20,000 deaths, mostly in developing countries. The problem is even more difficult because few new compounds are coming to replace old insecticides if any. The cost of creating and registering new pesticides is staggering at almost US $ 60 million, and pesticide manufacturers are unwilling to risk investments in products whose market life could be shortened by the development of pest resistance.

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

Pest control potential of Neem

However, the pest control potential of neem in developing countries remained mostly untapped due to the advent of DDT and other and other broad-spectrum synthetic insecticides. Also, wide publicity given to slogans such as “the only good bug is a dead bug” and identifying traditional uses of neem as backward gradually influenced people away from using neem.

It is only in the past decade that the pest control potential of neem, which does not kill pests but affects their behavior and physiology, has been recognized. Though subtle, neem’s effects include repellent, feeding and oviposition deterrence, growth inhibition, mating disruption, chemo-sterilization, etc. Neem is far more desirable than a quick knock-down in an integrated pest management program. They reduce the risk of exposing pests’ natural enemies to poisoned food or starvation.

Despite high selectivity, neem derivatives affect 400 to 500 species of insects belonging to Blattodea, Caelifera, Coleoptera, Dermaptera, Diptera, Ensifera, Heteroptera, Homoptera, Hymenoptera, Isoptera, Lepidoptera, Phasmida, Phthiraptera, Siphonaptera, and Thysanoptera. The ostracod species, several species of mites and nematodes, and even noxious snails and fungi, including aflatoxin-producing Aspergillus Flavus.

Blood-sucking Pests

Neem products repel and affect the development of mosquitoes. When applied to exposed body parts of human volunteers, two percent neem oil mixed in coconut oil provided complete protection for 12 h from bites of all anophelines. Kerosene lamps containing 0.01-1% neem oil, lighted in rooms containing human volunteers, reduced mosquito biting activity, and catches of mosquitoes resting on walls in the rooms; protection was greater against Anopheles than against Culex.