The Vivekananda Institute of Biotechnology (VIB), Nimpith, works mainly with small and marginal farmers in the Sunderbans region of West Bengal. Many of these farmers cannot afford synthetic pesticides, and the area's fragile ecosystem, which includes paddy fields, ponds, brackish-water fisheries and mangroves, is easily harmed by chemical runoff. Against this background, VIB has popularised a low-cost method for turning locally available neem (Azadirachta indica) seeds into an effective botanical pesticide. The main product is Neem Seed Kernel Extract (NSKE), and the technology is well suited to rural areas because every step can be carried out by farmers themselves, using simple household tools and no outside inputs.
Collection of ripe fruits. Neem trees fruit mainly during the monsoon months (roughly June to August). Ripe fruits are yellowish and drop naturally from the tree, so farmers can gather them from the ground. Fully ripe fruits give kernels with the highest content of active compounds.
De-pulping. The fleshy pulp around the seed is removed, usually by rubbing the fruits with water, sometimes with a little sand, and then washing. Pulp left on the seed ferments and encourages mould growth, which lowers the quality of the seed.
Drying and storage. The cleaned seeds are dried in the shade rather than in direct sunlight, because the main active compound, azadirachtin, breaks down under ultraviolet light and heat. Dry seeds are stored in well-aired gunny bags or baskets, not in airtight plastic, since damp seeds quickly become mouldy and lose their activity.
Decortication. The hard outer seed coat is removed by gently pounding the seeds in a wooden pestle and mortar (dheki or ukhli in local use) and winnowing away the husk. The kernel is the part rich in active principles, so separating it gives a more potent extract.
Grinding of kernels. The kernels are pounded in the same pestle and mortar into a coarse powder. This is best done shortly before the extract is prepared, since powdered kernels lose activity faster than whole seeds.
Preparation of the aqueous extract. For the commonly recommended 5% NSKE, about 50 g of kernel powder is used per litre of water. The powder is tied loosely in a muslin cloth and soaked overnight (about 12 hours). The cloth bag is then squeezed and the liquid filtered. A small amount of soap solution or another emulsifier is added so that the spray spreads and sticks well on leaf surfaces.
Spraying. The extract is sprayed on crops with an ordinary knapsack sprayer, preferably in the late afternoon or evening, when sunlight is weaker and the active compounds last longer. Because azadirachtin breaks down within a few days in the field, repeat sprays at intervals of about 7 to 10 days are usually needed during pest outbreaks. The extract should be used on the day it is made.
Neem is effective against more than 200 insect species, as well as some nematodes, fungi, bacteria and viruses. Unlike conventional insecticides, it rarely kills pests outright. Instead, its limonoid (tetranortriterpenoid) compounds affect insect feeding, growth and reproduction in several ways.
Azadirachtin is the most important compound. It acts as a strong antifeedant, so insects stop eating treated leaves. It also works as an insect growth regulator by interfering with the hormone ecdysone, which controls moulting. Affected larvae fail to moult properly, become deformed, or die in the larval or pupal stage. It also reduces egg laying and fertility in adult insects.
Salannin is mainly an antifeedant and repellent. Nimbin and nimbidin have antifungal, antibacterial and antiviral properties. Gedunin has antifungal activity.
Because neem contains a mixture of many active compounds acting by different mechanisms, it is very difficult for insects to develop resistance to it, which is a common problem with single-molecule synthetic pesticides. Neem products also have very low toxicity to humans, livestock, birds and fish, break down quickly in the environment, and are relatively gentle on natural enemies such as spiders, ladybird beetles and parasitic wasps, and on pollinators. This makes them well suited to integrated pest management (IPM).
Neem trees grow widely in India and other tropical countries, often along roadsides, village boundaries and homesteads, so the raw material is free or very cheap. The active compounds dissolve readily in water, so no solvents, machinery or laboratory facilities are needed. The technology keeps money in the village, reduces dependence on purchased chemicals, and avoids the health risks farmers face when handling toxic pesticides without protective equipment.
Nothing from the neem seed is wasted. VIB promotes three products:
Kernel extract (NSKE) for foliar spraying against insect pests.
Neem oil, obtained by pressing the kernels, which can be emulsified with soap and water and sprayed. It is especially useful against sucking pests such as aphids, whiteflies and mites, and also has some antifungal effect.
Neem cake, the residue left after oil extraction, which is applied to the soil. It adds organic matter and plant nutrients (nitrogen, phosphorus and potassium), suppresses soil nematodes and some soil-borne pathogens, and slows the conversion of nitrogen fertiliser into nitrate, so that nitrogen stays available to the crop for longer. This last property is the basis for neem-coated urea, which the Government of India has promoted widely.
It has been estimated that 20 to 30 kg of neem seed, roughly the average annual yield of two mature trees, is enough to prepare kernel extract for treating one hectare of crop. This means a few trees on a farmer's own land or in the village can meet the needs of his fields.
NSKE is particularly effective against cutworms (such as Agrotis species), which cut young seedlings at ground level and damage vegetables, maize, tobacco and coffee. It is also used against leaf-eating caterpillars, diamondback moth on cabbage and cauliflower, pod borers, leaf miners, aphids, jassids, whiteflies and several rice pests.
VIB has standardised the production and application of NSKE for the crops grown in this region, working out suitable concentrations, spray timings and intervals for local vegetables, paddy and other crops. Field demonstrations using NSKE are being carried out in different parts of the Sunderbans under a project funded by the Ministry of Chemicals and Fertilizers, Government of India. These demonstrations let farmers see the results on their own fields, which is the most convincing way to encourage adoption.
A balanced view should also note some drawbacks. Neem acts more slowly than synthetic insecticides, so farmers need to spray early, when pest numbers begin to rise, rather than waiting for heavy damage. The extract must be freshly prepared and sprayed repeatedly because it breaks down quickly in sunlight. The azadirachtin content of seeds varies with the tree, the location, the season and the storage conditions, so the strength of home-made extracts is not uniform. Seeds that are stored damp can become mouldy, which reduces their activity and can introduce fungal contamination. Proper drying, storage and farmer training are therefore essential to get consistent results.
The NSKE technology promoted by VIB is a good example of appropriate technology: it uses a locally available resource, simple tools and traditional knowledge, supported by scientific standardisation. It gives farmers an affordable and safe means of pest control, reduces the use of harmful chemicals in an ecologically sensitive region, and returns the leftover neem cake to the soil as a fertiliser and soil conditioner.