I claim:1. A method for preparing an azadirachtin-containing concentrate from an azadirachtin-containing plant oil which method comprises mixing with said oil a sufficient amount of a non-polar solvent in which azadirachtin has low solubility to produce an azadirachtin-containing precipitate, thereby precipitating said azadirachtin-containing concentrate.2. A method according to claim 1 wherein said non-polar solvent is a hydrocarbon selected from the group consisting of aliphatic, aromatic and alicyclic hydrocarbons, and mixutres thereof.3. A method according to claim 1 wherein the hydrocarbon is selected from the group consisting of pentanes, hexanes, heptanes, octanes, nonanes and decanes, and mixtures thereof.4. A method according to claim 1 wherein said non-polar solvent is selected from the group consisting of hexanes, heptanes and petroleum ethers.5. A method according to claim 1 wherein said azadirachtin-containing plant oil is a neem oil.6. A method for preparing an azadirachtin-containing concentrate comprising the steps of:(a) grinding, flaking or pressing an azadirachtin-containing plant material to produce an azadirachtin-containing expelled oil and a solid expeller cake;(b) optionally repeating step (a) to remove additional plant oils and azadirachtin from said expeller cake;(c) mixing the expelled oil with a sufficient amount of a non-polar solvent in which azadirachtin has low solubility to produce an azadirachtin-containing preciptate, thereby precipitating said azadirachtin-containing concentrate; and(d) collecting the azadirachtin-containing concentrate.7. A method according to claim 6 wherein said non-polar solvent is a hydrocarbon selected from the group consisting of aliphatic, aromatic and alicyclic hydrocarbons, and mixtures thereof.8. A method according to claim 7 wherein the hydrocarbon is selected from the group consisting of pentanes, hexanes, heptanes, octanes, nonanes and decanes, and mixtures thereof.9. A method according to claim 6 wherein said non-polar solvent is selected from the group consisting of hexanes, heptanes and petroleum ethers.10. A method according to claim 6 wherein said collecting is accomplished by decantation, filtration, centrifugation, or a combination thereof.11. A method according to claim 6 wherein the azadirachtin-containing concentrate from step (d) is dried to remove excess solvent.12. A method according to claim 6 wherein said azadirachtin-containing plant material is a neem seed material.13. A method for preparing an azadirachtin-containing concentrate comprising the steps of:(a) mixing an azadirachtin-containing plant material with a polar solvent, thereby forming an extract containing azadirachtin and plant oil;(b) optionally repeating step (a) to remove additional plant oil and azadirachtin from said plant material;(c) removing excess polar solvent from said extract to yield an azadirachtin-containing plant oil;(d) mixing said extracted oil with a sufficient amount of a non-polar solvent in which azadirachtin has low solubility to produce an azadirachtin-containing precipitate, thereby precipitating said azadirachtin-containing concentrate; and(e) collecting the azadirachtin-containing concentrate.14. A method according to claim 13 wherein said polar solvent is selected from the group consisting of ketones, alcohols, esters, ethers, nitriles, amides, sulfoxides, substituted aliphatic hydrocarbons, aromatic hydrocarbons, and substituted aromatic hydrocarbons, and mixtures thereof.15. A method according to claim 13 wherein said polar solvent is selected from the group consisting of acetone, benzene, dichloromethane, ethanol, ethyl acetate, ethylene dichloride, methanol, methyl acetate, methyl t-butyl ether, methyl formate, 2-propanol, toluene and xylene, and mixtures thereof.16. A method according to claim 13 wherein said polar solvent is ethylene dichloride or dichloromethane.17. A method according to claim 13 wherein said non-polar solvent is a hydrocarbon selected from the group consisting of aliphatic, aromatic and alicyclic hydrocarbons, and mixtures thereof.18. A method according to claim 17 wherein the hydrocarbon is selected from the group consisting of pentanes, hexanes, heptanes, octanes, nonanes and decanes, and mixtures thereof.19. A method according to claim 13 wherein said non-polar solvent is selected from the group consisting of hexanes, heptanes and petroleum ethers.20. A method according to claim 13 wherein the azadirachtin-containing concentrate from step (e) is dried to remove residual solvents.21. A method according to claim 13 wherein said azadirachtin-containing plant material is a neem seed material.22. A method for preparing an azadirachtin-containing concentrate comprising the steps of:(a) grinding, flaking or pressing an azadirachtin-containing plant material to produce a mechanically expelled azadirachtin-containing oil and a solid expeller cake;(b) mixing the expeller cake with a suitable polar solvent, thereby forming an extract containing azadirachtin and plant oil;(c) optionally repeating one or both of steps (a) and (b) to remove additional azadirachtin and plant oil;(d) removing excess solvent from said extract to yield an azadirachtin-containing plant oil;(e) mixing the expelled oil or extracted oil, either individually or combined, with a sufficient amount of a non-polar solvent in which azadirachtin has low solubility to produce an azadirachtin-containing precipitate, thereby precipitating an azadirachtin-containing concentrate; and(f) collecting the azadirachtin-containing concentrate.23. A method according to claim 22 wherein said polar solvent is selected from the group consisting of ketones, alcohols, esters, ethers, nitriles, amides, sulfoxides, substituted aliphatic hydrocarbons, aromatic hydrocarbons and substituted aromatic hydrocarbons, and mixtures thereof.24. A method according to claim 22 wherein said polar solvent is selected from the group consisting of acetone, benzene, dichloromethane, ethanol, ethyl acetate, ethylene dichloride, methanol, methyl acetate, methyl t-butyl ether, methyl formate, 2-propanol, toluene and xylene, and mixtures thereof.25. A method according to claim 22 wherein said polar solvent is ethylene dichloride or dichloromethane.26. A method according to claim 22 wherein said non-polar solvent is a hydrocarbon selected from the group consisting of aliphatic, aromatic and alicyclic hydrocarbons, and mixtures thereof.27. A method according to claim 26 wherein the hydrocarbon is selected from the group consisting of pentanes, hexanes, heptanes, octanes, nonanes and decanes, and mixtures thereof.28. A method according to claim 22 wherein said non-polar solvent is selected from the group consisting of hexanes, heptanes and petroleum ethers.29. A method according to claim 22 wherein the azadirachtin-containing concentrate from step (f) is dried to remove excess solvent.30. A method according to claim 22 wherein said azadirachtin-containing plant material is a neem seed material.31. A method for preparing a precipitate fraction of neem oil comprising the steps of:(a) mixing said neem oil with a sufficient amount of a non-polar solvent to form a precipitate;(b) collecting said precipitate; and optionally(c) drying the precipitate from step (b) to remove residual solvent.32. A method according to claim 31 wherein said non-polar solvent is a hydrocarbon selected from the group consisting of aliphatic, aromatic and alicyclic hydrocarbons, and mixtures thereof.33. A method according to claim 32 wherein the hydrocarbon is selected from the group consisting of pentanes, hexanes, heptanes, octanes, nonanes and decanes, and mixtures thereof.34. A method according to claim 31 wherein said non-polar solvent is selected from the group consisting of hexanes, heptanes and petroleum ethers.