1.2.2 Efficacy of neem-based pesticides

Comprehensive research on the effects of neem has been carried out around the world, mainly in India, Germany and the US, and in many other countries, often assisted by GTZ projects.

There is no doubt any more that neem extracts and products are effective in controlling a wide range of pests (Schmutterer 1995).

According to Schmutterer (1995, 1998) the neem-based extracts display an array of effects on insects, such as:

· antifeedancy
· reduction/prevention of settling and oviposition
· disturbance of metamorphosis
· sterilisation
· reduction of activity (fitness)
· effects on cell level (molecular level)

Despite the fact that neem is effective against a wide range of pests, it is much more selective than standard broad-spectrum pesticides in the pests and beneficial organisms it effects. Therefore it must be quite clear which pest is to be controlled in which crop, and sometimes even at which stage of the crop. Otherwise the application of neem will fail and the farmers will disappointedly turn away from this environmentally sound alternative.

One reason for some disappointment lies in the fact that "neem" does not always mean the same thing. To date more than 145 active ingredients have been identified (Morgan 1999), of which 40 are assumed or proven to have insecticidal properties.

· Azadirachtin (C₃₅H₄₄O₁₆), the most active insecticidal substance in neem seed, disrupts growth, prevents moulting, causes sterility of eggs, and other effects.

· Nimbin is a feeding repellent.

· Salannin inhibits feeding.

It is not known exactly which synergistic or additional effects the other ingredients or metabolites have. Even if pesticides are standardised, the quality parameter refers to the azadirachtin content only, despite the fact that the other active ingredients (Als) are as important or even more important against many pests. Therefore the need to select further Als for quality parameters is occasionally discussed (Foerster 1998). This, on the other hand, would increase the costs of quality control considerably.

The potential of the neem tree as a source of natural pesticides has been exploited in the production of neem-based pesticides in several countries, often at cottage or small-scale level.

The following table (Table 4) lists possible neem products for agricultural usage:

Table 4: Overview of various neem products and target pests: