Azadirachta indica has been used for centuries as the country store of developing nations. Earliest reference to it is in Sanskrit writings that are over 4,000 years old (Larson, 1990). Parts of this tree have been used for medicine, shade, building materials, fuel, lubrication, and most of all as pesticides. It is the use of this tree as an insecticide that now draws interest from industrialized countries. It is seen as an environmentally safe alternative to synthetic pesticides. To date over 195 species of insects are affected by this trees extracts at concentrations ranging from 0.1 to 1,000 ppm, and insects that have become resistant to synthetic pesticides are controllable with these extracts (Lindquist et al., 1990; Menn, 1990).
THE NEEM TREE
Azadirachta indica, commonly referred to in many countries as the neem tree, is a member of the Meliaceae family. This broad-leaved evergreen can reach heights of 30 meters with a trunk girth of 2.5 meters and live for over two centuries. Its deep root system is well adapted to retrieving water and nutrients from the soil profile, but this deep root system is very sensitive to waterlogging. The neem tree thrives in hot, dry climates where shade temperatures often reach 50 degrees celsius and annual rainfall ranges from 400 to 1,200 millimeters.
The tree can withstand many environmental adversities including drought and infertile, stony, shallow, or acidic soils. The neem produces ellipsoidal drupes, that are about two centimeters in length, borne on axillary clusters. These fruits contain kernels that have high concentrations of secondary metabolites (National Research Council, 1992).
There is evidence, but no scientific correlation, that trees grown in climates with lower rainfall produce kernels with higher content of metabolites (Schmutterer, 1990a).
The neem tree is believed to have originated in Assam and Burma of South Asia, but other reports suggest various areas of Pakistan, Sri Lanka, Thailand, Malaysia, and Indonesia (National Research
The tree also grows well in other tropical and subtropical areas around the world (Verkerk et al.,1993).
This is very important to commercial neem extract production so that a broad raw material base for industrial refinement can be established. Neem trees have successfully been established in Australia, Haiti, West Africa, the Dominican Republic, Ecuador, Puerto Rico, the Virgin Islands, and in the continental United States in Florida, California, Oklahoma, and Arizona (Jacobson, 1990; Schmutterer, 1990a; Verkerk et al.,1993).
The trees growing in Arizona are part of a breeding and selection program aimed at developing a variety that will be frost tolerant to temperatures as low as 18 degrees below zero celsius. Such a development would allow this tree to be established in many more regions. The seed for this project was obtained from natural tree populations growing in northern India where the climate is cooler than most areas where neem grows (Jacobson, 1990).
Cultivation of the neem tree is also an important consideration as the tree is established in new regions. Very little problems arise in vegetative propagation. Transplanting seedlings, saplings, or root suckers achieves a high success rate (National Research Council, 1992).
Seeds are more desirable to use when transporting a long distance for ease of packing, however, minor problems have been observed when growing these trees from seeds. It was found that dry or unripe seeds would rot in soil. Large scale establishment of neem trees required germination in sand, transplanting to clay pots after a month, and then planting in the field when the seedlings reached 30 to 45 centimeters in height (Jacobson, 1990).