|Title of Invention||
"ADDITIVES FOR IMPROVED PHOTOSTABILITY OF AZADIRACHTIN-A"
|Abstract||The elfcctiveness persistence and scope of use of many pesticides are limited or restricted by their stability, particularly to sunlight. The present invention relates to a process for preparation of photostable technical azadirachtin-A concentrate (a neem based pesticide), for use in the pest control of Spodoptera litura in the field by use of an effective amount of toxicologically safe additives to photolabile technical azadirachtin-A concentrate.|
|Full Text||Description of Invention Field of Invention
This invention relates to increasing the photostability of azadirachtin-A (a neem based pesticide) by use of
lexicologically safe additives to allow it to be used for an extended time period in the field for the control
of agricultural pests (ex. Spodoptera litura).
Background of Invention
In view of the various harmful effects of synthetic pesticides (mammalian toxicity, residues, pest
resistance, pest resurgence etc.), neem pesticides are finding increased application in agricultural and public health pest control. Being organic in nature these are biodegradable and have been found to be devoid of various harmful effects associated with the use of the synthetics. Azadirachtin-A has been established globally as the principal bioactive constituent of neem responsible for the multifarious effects such as insect growth regulation, antifeedency, toxicity, insect sterility etc. against a wide spectrum of insect pests. Due to this, neem products are internationally standardised based on their azadirachtin-A content.
The photo, thermo and bio-lability of azadirachtin-A has recently been realised as the biggest bottleneck in the promotion of quality neem pesticides with the desired shelf life. Azadirachtin-A is decomposed by light, particularly, by ultra violet light (290-320 nm)., therefore can occasionally be used outdoor.. It would be advantageous if a azadirachtin-A composition could be formulated which is sufficiently light stable so as to be usable outdoors and yet it could decompose after a selected time of use outdoors so as to prevent any environmental damage, toxicity problems with higher animals, and the like.
Attempts have been made in the past to stabilize azadirachtin-A by use of additives. These attempts have generally consisted of adding antioxidants and /or light absorbers which act as UV screens in the 290-320 nm range ( see, for example, Sundarams, K.M.S and Curry, J., (1996)Chemosphere Vol. 32(4): 649-658; , K.M.S and Curry, J., (1996) Jour. Environ. Sci. Health, B31(5):101-1069, ; Chowdhary, H. (1997) Ph.D thesis, PC School. IARI (New Delhi), India; Khan, M.A. (1998) Ph.D thesis, PG. School, IARI, New Delhi) .While attempts to stabilize azadirachtin-A have met with some success, such success has only been sufficient to allow limited outdoor use of normally photolabile azadirachtin-A insecticide.
In view of the various harmful effects of synthetic pesticides (mammalian toxicity, residues, pest
resistance, pest resurgence etc.), neem pesticides arc finding increased application in agricultural and public health pest control. Several reports describing development and use of such pest control chemicals are available in the prior art. The concept of adding additives/photostabilizers to azadirachtin-A is not new. An US Patent 5,352,697 discloses that addition of various types of vegetable oil epoxides to azadirachtin results in compositions with improved storage stability. US Patent No. 4,556,562 discloses stable anti pest neem seed extract that is storage stable composition effective as a biorational agent for protection against pests, e.g. Japanese beetle; another US Patent 4,946,681, discloses the method to prepare an improved storage stable neem seed extract that is a process for the production of stable azadirachtin solutions comprising extracting ground neem seeds with a solvent having azadirachtin solubility to produce an aqueous-containing azadirachtin extract solution and then adding an effective amount of 3-4 Angstrom molecular sieves to selectively remove water from the extract to yield a storage-stable azadirachtin solution
having less than 5% water by volume. A number of other patents such as US Patent 5,001,146; 5,124,349; 5,281,618; 5,391,779; 5,695,763; 5.827,521 disclose storage stable azadirachtin formulations.
Although several reports are available on the use of additives for improving the photostability of a/.adirchtin-A, this invention differs from earlier reports is that the newly discovered additives are more effective than previously reported to achieve the stability of photolabile azadirachtin-A rich technical concentrate. An in depth investigation was thus necessitated. This invention provides new composition that is highly effective as pest control agent. Objects of the Invention
An objective of the invention is to search for lexicologically acceptable additives, which can stabilize photolabile azadirachtin-A and allow it to be used for an extended time period in the field for the control of agricultural pests (ex. Spodoptera litura). The invention
In accordance with the present invention, there is provided a process for the preparation of photostable azadirachtin-A rich concentrates by addition of an effective amount of lexicologically safe additives which significantly decreases the rate of the photochemical decomposition reaction of the azadirachlin-A. The product so obtained has been found to be more stable lhan azadirachlin-A and has improved persislence. bioactivity againsl Spodoptera litura and other allied advantages.
. The method comprises admixing with the azadirachtin-A an effective amount of a lexicologically safe addilive. In accordance with slill anolher embodimenl of Ihe presenl invenlion, a melhod is sel out of studying insect growth regulatory and anlifeedanl activity with azadirachlin-A which is decomposed when exposed lo lighl for a selecled time period during its use. The method comprises admixing a photolabile a/adirachlin-A having an insecticidal effectiveness period in the dark al least as greal as Ihe selecled lime period and in Ihe lighl significantly less lhan Ihe selected time period with an amount of a lexicologically safe addilive which decreases the rale of the pholochemical decomposilion reaclion of Ihe azadirachtin-A sufficiently so thai Ihe resultant admixture has an insecticidal effectiveness period when exposed to light during ils use equal to the selected time period and exposing insects to the thus oblained admixture.
Pesl conlrol requires the use of bioactive chemicals wilh suitable persislence lo prolecl Ireated surfaces from pest invasion or attack for several hours or days or lo kill insects contacling Ihe Ireated surfaces. The effectiveness and use areas for a pesticide are often delermined by ils persistence. A short residual insecticide may be best for one situation and a longer persislence chemical for anolher pest or use. An ideal situation involves an additive lhal is generally lexicologically safe and lhal can be inlroduced in varying amounts to achieve the desired degree of persislence. Azadirachlin-A (neem based pesticide) is one type of pesticide where Ihis would be of value. When operating in accordance wilh Ihe presenl invenlion, compositions are provided which have these properties. Best mode for carrying out the invention
In accordance with Ihe presenl invenlion, it has been discovered thai certain additives can be admixed wilh azadirachlin-A (which is not pholostable) to provide insecticidal compositions having a
desired degree of photostability. Many of the additives are relatively inexpensive, particularly compared to the cost of azadirachtin-A. Accordingly through the use of small amounts of inexpensive lexicologically safe additives, the effectiveness period of azadirachtin, when exposed to light during their use, can be significantly increased.
As has been alluded to previously, a useful additive must be toxicologically safe in thai it must generally be non-toxic, non-carcinogenic and non-allergenic. The term lexicologically safe is used herein lo indicate that while the additive may have some loxic, carcinogenic or allergenic properly, the degree of such property must be so slight as to cause no significant problem when additive is used in the manner and in the concenlralion contemplated.
The addilives, which have been found lo be effeclive in slabilising phololabile azadirachlin-A, have certain allribules in common. These addilives acl lo decease Ihe rale of photochemical decomposition of a/.adirachlin-A at a given light level. The slruclure of azadirachlin-A has been given below wilh phololabile sites. Several factors influence or determine the pholoslabilising activity of the addilives of Ihe presenl invention. A photochemical interaction appears to be involved between azadirachtin-A and Ihe additive since differenl yields and/of major reaction producls are oblained when the azadirachtin-A is irradiated wilh and without additives. The stabilisation provided by the addilives serves lo decrease Ihe role of the pholodecomposlion processes
Particularly effective stabilisation has been found wilh the addilives namely 2,4-dihydroxy acetophenone. ter-butyl hydroquinone, 8-lrydroxy quinoline, ter-butyl cresol, ter- butyl calechol and catechol. Of lesser but still subslanlial effectiveness are 2-hydroxy biphenyl, 4-hydroxy biphenyl, 2-hydroxy acelophenone, 4-hydroxy acetophenone. A number of additives have been screened which have litlle or no effectiveness in stabilizing azdirachlin-A . Such addilives include biphenyl, acetophenone, neem oil, linseed oil, castor oil, olive oil, nimbin, salannin, nicotine, citral, benzoin, coumarin, gallic acid, slilbene, diphenylamine, dibulyl phlhalale, riboflavin, rose bengal, phloroglucinol, O-phenylene diamine, ethyl cinnamale, pyragallol, benzophenone and p-amino benzoic acid.
As will be apparent from Ihe proceeding paragraph significant photostabilisation is attainable using additives , which are monocyclic aromatic compounds having a ter-bulyl or hydroxy group attached to the ortho or para position of the monocyclic aromatic ring .
The amount of additive added may vary greally depending upon Ihe desired period of effectiveness for the insecticidal composition. Amounts as little as one part of Ihe slabilizer per 100 parts of
azadirachtin-A have considerable stabilising effect, particularly when additive chosen is one of the most effective stabiliser, as set out above.
The invention will be better understood by reference to the following illustrative examples, which set out actual tests run utilising azadirachtin-A and various additives.
Effects of various candidate additives on azadirachtin photodegradation
The azadirachtin-A (l00mg) and the candidate additive (100 mg) were exposed to light (254 - 400) for 24 hours and sunlight for 72 days as thin film obtained by applying appropriate volumes of a acetone stock solution. After exposure the plates were extracted and azadirachtin content was estimated by HPLC. The Table 1 and as obtained in this example illustrate the very striking effectiveness of the additives in accordance with the present invention, when used in a one to one mixture with azadirachtin-A.
Table 1: Effectiveness of various additives on photo stability of technical azadirachtin-A concentrate
Table 2: Half life of technical azadirachtin-A concentrate with or without additive under sunlight
The results clearly reveal the stability of the azadirachtin-A with additives over azadirachtin-A.
EXAMPLE 2 INSECT TESTS
The insect growth regulatory and antifeedant bioactivities of azadirachtin-A and azadirachtin-A along with additives in the ratio of 5 parts a/adirachtin to 1 part additive by weight (exposed to sunlight for 30 days) were evaluated against the first instar neonate and fifth instar larvae of Spodoptera litura respectively, and are reported in Tables 3 and 4.
Table 3: Insect growth regulatory activity of technical azadirachtin-A concentrate with and without additives against first instar neonate larvae of S litura after 30 days of irradiation under sunlight-
Table 4: Antifeedant activity of technical azadirachtin-A concentrate with and without additives against fifth instar larvae of Spodoptera litura 30 days of irradiation under sunlight
This example illustrates the effectiveness of one of the preferred additives of the present invention in stabilising azadirachtin-A against photodecoinposition and also the stabilised azadirachtin-A is without any adverse effect on the bioactivity.
Effect of lesser amounts of additives
The candidate additives were tested in various ratios to azadirachtin-A utilising the chemical procedure indicated in example 1 but only under UV light. . The results are set out in Table 5
Table 5: Effect of additive concentration on percent recovery of azadirachtin-A after exposure to UV- light for 12 hours
The invention operates to provide an insecticidal composition of controllable persistence. It also allows azadirachtin-A to be effectively utilised for relative long periods outdoor which have previously only been effectively utilised for short periods outdoors.
1. A process for the preparation of photostable technical a/adirachtin-A concentrate for use in the pest control of Spodoptera litura comprising in addition of an effective amount of lexicologically safe additive to photolabilo technical a/.adiraclnin-A concentrate, Wherein a/adirachtin-A to additive ratios range between 1 : 1 or 1 :0.5 w/w.
?.. A process as claimed in claim 1 wherein the technical a/adirachtin-A concentrates include (he enriched azadirachtin-A concentrates containing 5% and above of azadirachtin-A.
3. A process as claimed in claim I wherein the additive is toxieologically safe organic compounds such
as ter-butyl hydroquinone or 8-hydroxy quinoline or ter-butyl cresol.
4. A process for preparation of photostable technical azadirachtin-A concentrate for use in pest control
|Indian Patent Application Number||460/DEL/2001|
|PG Journal Number||13/2009|
|Date of Filing||04-Apr-2001|
|Name of Patentee||INDIAN COUNCIL OF AGRICULTURAL RESEARCH|
|Applicant Address||KRISHI BHANWN, DR. RAJENDRA PRASAD ROAD, NEW DELHI-110001|
|PCT International Classification Number||A01N 65/00|
|PCT International Application Number||N/A|
|PCT International Filing date|