Storage stable pesticide formulations containing azadirachtin

Details Storage stable pesticide formulations containing azadirachtin Storage stable pesticide formulations containing azadirachtin

2000-03-27

2004-11-02

Levy, Neil S. (Department: 1616)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Biocides; animal or insect repellents or attractants

C424S195110, C424S405000, C424S761000, C514S027000

Reexamination Certificate

active

06811790

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to pesticide formulations and more particularly relates to storage stable pesticide formulations containing azadirachtin.
Extracts of various parts of the neem tree (
Azadirachta indicia
) such as leaves, bark, seeds, etc. have been long known to have insecticide activity. The seed kernel, in particular, processes the most active limonoids, such as Azadirachtin A and B and structurally related compounds such as C, D, E, F, G, H, I, J, K, and the like, along with nimbin, salannin, azadiradione, and the like. All of the natural azadirachtins have been reported to have a very high growth disturbing activity against
Epilachna varivestis
, with LC
50
s in the range of 0.3 to 2.8 ppm (H. Rembold and I Puhlmann, 1995). More than 100 terpenoid metabolites are reported from the neem seed/fruit of the neem tree. Various methods have been described to extract these active components in the crude or semi crude forms to be used in commercially acceptable vehicles in the form of liquid and solid formulations. The crude neem seed extracts obtained after removal of lipid components normally contain 20-45% of Azadirachtin A and B and have been shown to be potent insect growth regulators and feeding deterrent and form potential active ingredients in commercial pest control formulations. The active molecules of the neem seed extracts are rather large and complex, and having acid and base sensitive functional groups they tend to be unstable in these vehicles, thus posing a major limitation for commercial use of these extracts.
So far, azadirachtin has been widely formulated in liquid forms to be applied as an emulsion or solution to agriculture crops. Various organic solvents and other inorganic additives have been used as carriers in order to make a cost effective and efficacious delivery system. The use of such carriers is rather limited, however, since many solvents are deleterious to the stability of azadirachtin. Dureja (1999) has studied the degradation of azadirachtin A in various solvents for 25 days at 29+/−1° C. The results indicated 50% degradation of azadirachtin A in methanol and acetone, 75-80% degradation in methylene chloride, carbon tetrachloride and chloroform and about 80% degradation in ethanol and water.
Storage-stable azadirachtin formulations and methods of preparing stable azadirachtin compositions have been proposed. U.S. Pat. No. 4,556,562 reports that the stability of azadirachtin in ethanol emulsions increased by diluting the concentration of azadirachtin to between 2000 and 4000 ppm and adjusting the pH to between 3.5 and 6.0. U.S. Pat. No. 4,946,681 (Walter) reports greater stability for azadirachtin in solutions of aprotic solvents containing less than 2-5% of water. U.S. Pat. No. 5,001,146 indicates that azadirachtin stability is improved by adjusting the concentration of polar aprotic solvent to at least 50% by volume and by decreasing water content to less than 15% by volume. Moreover, U.S. Pat. No. 5,001,146 further indicates that azadirachtin stability depends upon the type of solvent employed, and that stability requires storage in large quantities of certain enumerated aprotic and alcohol solvents. Murali (U.S. Pat. No. 5,736,145) reports a storage stable aqueous composition containing azadirachtin A and U.S. Pat. No. 5,827,521 indicates a stable azadirachtin formulation containing aliphatic dihydroxylated alcohols of more than 80% by volume and optionally with sunscreens and antioxidants.
U.S. Pat. No. 5,352,697 describes the enhancement of stability of azadirachtin in solution by the presence of epoxide, preferably an epoxidized vegetable oil. These methods describe the enhancement of azadirachtin containing extracts in the liquid form prepared from neem seed kernel with organic solvents.
European Patent No. 9216109 describes making an extract of neem seed in solid form with greater stability. The stability of azadirachtin in neem extracts is reported to be improved by removing the lipid impurities from extracts (Indian Patent Application No. 1855). Walter (U.S. Pat. No. 5,635,193) reports that an azadirachtin containing solid is stable by limiting moisture and volatile polar solvents to less than 1% and 5%, respectively. A formulation containing 0.05% to 2% surfactant and 99% of solid diluent has been claimed as a stable bio-control agent by retention of at least 75% of azadirachtin after 2 weeks of storage at 54° C. Such a formulation may be used as a dust and wettable powder, but the efficacy of azadirachtins in such vehicular formulations is not practically reported.
Another formulation is a solid form of neem seed extract prepared from the kernel of neem seed as per the methods described in U.S. Pat. No. 5,695,763, European Patent No. 9,216,109, and IN 181,845. The product is quite stable with respect to its active ingredients viz Azadirachtin A, B, nimbin, salannin and the like.
Though, various extracts with stable Azadirachtin have been reported, stability of azadirachtin in a formulated state is still a concern. Azadirachtin is highly unstable in various surfactants, organic solvents, and in different combinations of solvent and surfactants in liquid formulations which is a serious limitation for the development of a shelf stable commercial product.
Normal pesticide formulations contain various solvents made mostly from petroleum, and there is a concern that usage of such solvents in specialty pesticide formulations, especially meant for organic farming, veterinary application, and the like, is discouraged. The use of such solvents, even at a lower rate, demands large amounts of surfactants and other additives which makes the cost of the formulations high. The use of a broader range of ingredients in liquid formulations and the associated problem of instability in such formulations is also a serious concern for the commercial success of azadirachtin containing crop protection agents. Accordingly, there is still a need for a formulation containing simple, safe, and cost effective vehicles which yet provides stable and efficacious products.
Various plant oils such as neem oil, castor oil, acorus oil, and sesame oil, have been used in specific end use applications as additives for enhancing the efficacy of formulations by synergism. These oils may be ideal substitutes to organic solvents but at higher concentrations these may cause phytotoxicity and instability to the active ingredients of the formulation. The advantage of sesame oil as a natural synergist to synthetic pyrethroid insecticides has been demonstrated. The possibility of increasing the efficacy of various neem seed extracts against different insects by addition of sesame oil has been examined. M. Schauer (1983) has reported that lecithin II with sesame oil has improved the effect of a neem extract obtained from methyl-tertiary-butyl-ether in achieving higher mortality of
Acyrthosiphon pisum
and
Aphis fabae
. N. Z. Dimetry et al. have reported that addition of sesame oil to commercial neem formulations containing azadirachtin has increased insecticide efficacy of the formulations against adult apids,
Aphis craccivora
. While these reports indicate that sesame oil may enhance the efficacy of neem extracts, no one has studied its effect on the stability of most active compounds of neem extracts such as azadirachtins which is an important aspect for development of commercial formulations.
Accordingly, there is a need to develop environmentally safe pesticide formulations which contain azadirachtin and which are further storage stable and economical.
One aim of the present invention is to develop a delivery system for azadirachtin containing neem seed extracts, free from any solvent, less expensive, and completely soluble in water.
The present invention provides a composition of a neem seed extract and sesame oil, free from any organic solvents, with better efficacy and storage stability for azadirachtins.
All of the patents and publications mentioned throughout this application are incorporated herein in their entirety.

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