EP1876891A1

EP1876891A1 - Preparation of compositions with high insecticidal activity

Info

Publication number: EP1876891A1
Application number: EP06744529A
Authority: EP
Inventors: Modesto Giberti; Marco Pusinanti
Original assignee: Chemia SpA
Current assignee: Chemia SpA
Priority date: 2005-04-22
Filing date: 2006-04-20
Publication date: 2008-01-16
Also published as: ITMI20050730A1; WO2006111839A1

Abstract

The preparation of compositions with high insecticidal activity, characterised by the formation of insecticide-containing microcapsules which are dispersed in an emulsion or microemulsion of a compound having an activity synergistic with said insecticide is described. At the treatment stage, these compositions enable the synergistic product to act immediately, sensitising the insect before insecticide release occurs. The capsule then releases the insecticide with a sufficient time delay after the synergist has achieved its sensitising potential; the effect of the insecticide is thus amplified. The microcapsule walls can also be in a modified form by operating under specific polymerisation conditions, hence allowing an improved interlinkage between the actions of the two active compounds.

Description

PREPARATION OF COMPOSITIONS WITH HIGH INSECTICIDAL ACTIVITY

FIELD OF THE INVENTION

The present invention concerns the field of insecticide formulations in which the insecticide is combined with a synergistic compound that amplifies its activity. New insecticide compositions with improved activity are described, in which the insecticide is microencapsulated in a microcapsule with optionally modified walls, and is combined with an emulsion/microemulsion of a synergistic compound. PRIOR ART The problem of tolerance and resistance to pesticide activity is particularly serious and of growing importance, leading to the ever more difficult control and eradication of damaging insects both in agriculture and for veterinary and domestic hygiene applications. Many insects have strengthened their natural defences and immune systems against the toxins with which they come into contact, so that to achieve their eradication, dosages have to be increased or new insecticides or insect growth inhibitors must be continually used with consequent greater risks and damage to the entire ecosystem and the whole length of the food chain up to man, and with rising costs. The use of substances such as piperonyl butoxide (PBO) and its analogues sesamol, verbutin and MGK 264, able, in synergistic combination with insecticides, to inhibit the activity of certain insect metabolic enzymes involved in detoxification and pesticide resistance and hence able to enhance in vitro effectiveness of insecticides, is known in the literature [see for example Gunning et al., "Piperonyl Butoxide", pages 215-225, Academic Press (1998)]. With the aim of prolonging insecticidal activity over time while at the same time reducing contact toxicity to the spray operator, it is known for example to formulate the insecticide in the form of microcapsules or to complex it with cyclodextrin. Likewise, synergistic compositions are known in which, for example, a pyrethroid type insecticide and piperonyl butoxide as the synergistic substance are jointly encapsulated in polyurethane or polyamide (WO-A-97/14308). The patent application PCT/EP2004/051726 describes compositions in which the insecticide and the synergistic product are jointly complexed with cyclodextrin. In US 4524068, PBO complexed with cyclodextrin was found to be more effective than uncomplexed PBO.

The present invention proposes to significantly improve the performance of commercially known insecticides or insect growth regulators by means of a single treatment. SUMMARY

The Applicant has carried out studies to verify the possibility of achieving improved effects through the differential release of insecticide and synergistic product. It was discovered that by simultaneously administering insecticide-containing microcapsules and an emulsion of a synergistic compound or a microemulsion thereof, an unexpectedly high degree of insecticidal effect is achieved. The present invention relates to the preparation of insecticide compositions consisting of an emulsion or microemulsion of the synergistic compound contained in a suspension of insecticide-containing microcapsules. In the treatment stage said compositions allow the synergistic product to act immediately to sensitise the insect prior to insecticide release. The capsule then releases the insecticide with a sufficient time delay, after the synergist has already achieved its sensitising potential; the effect of the insecticide is thus amplified. In a preferred embodiment of the invention, the insecticidal effect is maximized by operating with microcapsules whose wall is modified. The Applicant's experimental data have shown that in this case the interlinkage between the action of the synergist and that of the insecticide is more effective. Modification of the wall can be achieved in various ways, depending on the type of polymer constituting the wall. In the present application two of these methods are exemplified. In the first case the materials to be encapsulated are reacted together, namely a diamine, a diisocyanate or polyisocyanate in slight excess, and a monofunctional amine, said amine being utilized in a quantity equal to or greater than the diisocyanate (or polyisocyanate) excess, in accordance with specific ratios. In a second exemplification, the material to be encapsulated is reacted with urea and formaldehyde in specific ratios. The emulsion or microemulsion of the synergistic product is formed by suitable techniques known in the field: the aforedescribed microcapsules are added to it in order to obtain insecticide compositions with improved activity.

DESCRIPTION OF THE FIGURES

Figures 1 and 2: ¹H NMR spectrum of a formulated product according to the invention

Figure 3: ¹H NMR spectrum of the capsular wall of a formulated product according to the invention

Figure 4: ¹³C NMR spectrum of the capsular wall of a formulated product according to the invention. DETAILED DESCRIPTION OF THE INVENTION

The insecticide contained within the microcapsule can be any compound with insecticidal activity. Such products are commonly known and can be chosen for example from the compounds belonging to the following classes: pyrethrum, pyrethroids, neonicotinoids, organophosphates, organic acaricides and natural insecticides such as azadirachtin, quassin, rotenone, nicotine, etc.

The percentage weight of insecticide relative to microcapsule weight is not critical and can vary according to the ranges commonly known in the field. The term "synergistic compound" means a product that does not possess insecticidal activity itself, but which sensitises the insect to insecticide treatment, for example by reducing/inhibiting insect detoxification systems useful for eliminating the insecticide. These compounds, generally to be associated with specific insecticides or classes of insecticides in accordance with the common knowledge of the field, are chosen for example from the following compounds: sesamol, piperonyl butoxide, verbutin, MGK 264 (N-octyl bicycloheptene dicarboximide) etc.

MGK 264 is both a mosquito repellent and a synergist. The MGK 264 molecule is of considerable size and is therefore poorly absorbed through the skin. Further examples of synergistic compounds are Deet (N,N-diethyl-m-toluamide): this is by far the most used insect repellent in the world, particularly against mosquitoes, ticks and other biting insects; R-326 (Di-n-propyl Isocinchomeronate) is the most active repellent against flies, gnats, no-see-ums and similar annoying insects. R-326 is far more effective than Deet against these insects and is active even at low doses. Further synergists are for example those belonging to the classes of essential oils and other products present in nature which exert repellent action against insects. Over 150 natural repellents can be counted, the most common of which being: citronella, eucalyptus, lemon leaves, peppermint, lavender, cedarwood oil, canola, rosemary, penny royal and cajeput. A further example of a synergistic compound is white mineral oil (isoparaffin). The quantity of synergistic compound contained in the emulsion or microemulsion is proportional to the quantity of insecticide contained in the microcapsules, according to ratios commonly used in the field for each insecticide/synergistic product pair. As a non limiting example the synergistic product can be present in a quantity 3-4 times greater than the active principle.

Optionally, a further portion of synergistic product (for example between 0.1 % and 70% by weight relative to the microcapsule weight) can be also present in the microcapsule, together with the insecticide; in this case the synergistic product is found both inside and outside the microcapsule. In this manner it is able to react not only prior to, but also during the insecticide release phase, thus allowing a continuous sensitisation of the insects during the entire treatment cycle. The capsular polymer can be any polymer usable in the production of microcapsules: non limiting examples are polyurea, polyamide, urea-formaldehyde polymers, etc. The monomers from which said polymers are obtained are currently known. In the case of polyurea the monomer pair diisocyanate/diamine can be used; in the case of polyamide the diamine/acyl chloride pair can be used, while the urea-formaldehyde polymer is obtained from the two respective components in the free state. The weight of the membrane is between 2 and 10% relative to the active principle, preferably 4 to 6%, even more preferably being 4.8.

The average microcapsule diameter is generally less than 50 micrometres, more preferably less than 10 micrometres. The process for forming the compositions of the invention comprises the following steps: a) mixing the insecticide and possibly a portion of synergistic product with the suitable monomer precursors of the capsular polymer, and polymerising the aforesaid monomers to obtain insecticide-containing microcapsules b) mixing the microcapsules obtained in (a) with an emulsion or microemulsion of a synergistic compound.

The microencapsulation procedure which characterises step (a) can be selected from known procedures such as microencapsulation by coacervation or interfacial polymerisation etc. The expert of the art can suitably select the most appropriate process depending on whether the substance to be encapsulated (insecticide and possible synergistic product) is in liquid or solid form at the required process temperature. Standard literature references to the aforesaid polymerisation reactions are for example K.J.Saunders in Organic Polymer Chemistry, 2^nd ed., pages 366-7 and Szycher's Handbook of Polyurethanes, CRC Press, 1999, pages 4-6 to 4-9, and D-1 to D-4.

Should a modified wall be required, operation under conditions of partial inhibition of polymerisation is possible. Modification is achieved by reducing the degree of polymerisation/cross-linking of the monomers forming the capsular polymer: this is done by using polymerisation inhibitors or by reducing the quantity of one of the co-monomers to a level below that necessary for complete polymerisation, or by undertaking the polymerisation under conditions of time, temperature, solvent etc. insufficient for complete polymerisation. A wall is obtained in which the capsular material is mechanically weaker and easier to dissolve.

In the case of polyurea, modification of the wall can be achieved with the methodology exemplified herein, which the Applicant has identified as being particularly suited to the purposes of the present invention. A suitable diisocyanate or polyisocyanate, the insecticide and the possible fraction of synergistic product to be encapsulated, are dispersed in water. Examples of diisocyanates/polyisocyanates are: Diphenylmethane diisocyanate (MDI), Toluene diisocyanate, lsophorone diisocyanate (mixture of cis- and trans-isomers), Diphenylmethane 4,4'-diisocyanate (mixture of di- and tri-isocyanates), Hexamethylene diisocyanate, 2-Methyl-1 ,3-phenylene diisocyanate, Methylene diphenyl isocyanate, Hexamethylene-1 ,6-diisocyanate, Polymethylene polyphenyl isocyanate (PAPI), lsophorone diisocyanate (IPDI), 1 ,5-Naphthalene diisocyanate (NDI), Methylene bis(4-cyclohexylisocyanate), aliphatic or aromatic isocyanate prepolymers (e.g. OCN-(CH₂)₆-N[CONH(CH₂)6NCO]₂ or C₂H₅-C(CH₂O-CO-NH- C₇H₄NCO)₃). A preferred example of a polyisocyanate is polymethylene polypheny! isocyanate (abbreviated herein to PMPPI, and also known as Voranate ®, Dow Plastics). Dispersion of the diisocyanate/polyisocyanate can be promoted with the aid of a surfactant.

An aqueous solution of a suitable diamine and a suitable monofunctional amine is then added. Examples of diamines are: Hexamethylenediamine (HMDA), N-(1- Naphthyl)ethylenediamine, 1 ,2-Phenylenediamine, 4-Aminodiphenylamine, Ethylenediamine, 4-Methy[-1 ,3-phenylenediamine, 4-Methyl-1 ,2- phenylenediamine, 1,8-Naphthalenediamine, 4-Nitro-1 ,2-phenylenediamine, 1 ,8- Diaminooctane, 1 ,4-Phenylenediamine, anhydrous Piperazine, 1 ,3- Diaminopropane, 1 ,4-Diaminobutane, 1 ,2-Phenylenediamine, 4- Aminodiphenylamine, 1 ,5-Diamino-2-methylpentane, 1 ,2-Diaminocyclohexane, 1 ,8-Diamino-3,6-dioxaoctane, 2,2-Dimethylpropylenediamine, 1 ,7-

Diaminoheptane, 1,9-Diaminononane, 2-Nitro-1 ,4-phenylendiamine, 1 ,3- Phenylendiamine, 1 ,2-Diaminopropane, 2-Methyl-1 ,5-diaminopentane, N- Phenylethylenediamine, N-lsopropylethylenediamine, N-Methylethylenediamine, N,N'-Dimethylethylenediamine. Particularly preferred are: HMDA, ethylenediamine, phenylenediamines, toluenediamines; the most preferred is HMDA.

The preferred monofunctional amine is NH₃. Other usable monofunctional amines are primary or secondary amines, such as: methylamine, dimethylamine, monoethylamine, diethylamine, butylamine, monoethanolamine, diethanolamine, isopropylamine, diisopropylamine, aniline, propanolamine, aminopyridine, cyclohexylamine, dibutylamine, N,N-dimethyltrimethylenediamine, benzylamine; Monofunctional alcohols can be used as alternatives to monofunctional amines in the presence of a suitable catalyst such as 1 ,4-diazabicyclo[2.2.2]octane (DABCO).

The ratio of diisocyanate (or polyisocyanate) equivalents to diamine equivalents used must be between 1.01 and 1.40, preferably 1.2. The equivalent weight of the diisocyanate or polyisocyanate (EW)NC_O, used for calculating the number of equivalents, is established based on the equation:

(EW)_NCO = (42 / K) x 100 where the constant 42 represents the molecular weight of the N=C=O group, K represents the percentage incidence of the two N=C=O groups relative to the total molecular weight of the diisocyanate used. For example, in the case of diphenyl methane diisocyanate (having a m.w. of 250.26) K is equal to (84/250.26) x 100 = 33.57; (EW)NC_O is equal to (42/33.57) x 100 = 125.11. In the case of polyisocyanates, the value of K varies according to the commercial polymer chosen, said value being always declared in the product specifications. In the examples, Voranate M220 was used, with a K of 30.9% and therefore with an equivalent weight of 135.9.

The equivalent weight of the diamine, for the purposes of the present invention, is calculated as % of its MW. The equivalent weight of NH₃ for the purposes of the present invention, is calculated as 1/3 of its MW (= 5.67).

As is apparent from the aforesaid 1.01-1.40 ratio, the operation is always carried out in a slight excess of diisocyanate (or polyisocyanate) equivalents relative to the diamine. The monofunctional amine is used in a number of equivalents equal to or greater than the excess of diisocyanate (or polyisocyanate) present, according to the equation: Z > (X-Y), where Z are the monofunctional amine equivalents and X and Y are the diisocyanate (or polyisocyanate) and diamine equivalents used.

The reaction between diisocyanate (or polyisocyanate) and diamine is undertaken preferably at a temperature between 10 and 80°C, for a time between 1 and 180 seconds.

In the case of urea-formaldehyde polymers, modification of the walls can be achieved with the methodology exemplified herein, identified by the Applicant as being particularly suited to the purposes of the present invention. Urea, formaldehyde, HCI and the active principle to be encapsulated are reacted together so that the molar ratio of urea to active principle is between 1.3 and 1.5, preferably equal to 1.4 and the formaldehyde to active principle ratio is between 1.6 and 1.8, preferably 1.7. The reaction with urea and formaldehyde takes place on the solid phase of the active principle and is thus suited to solid active principles, that is to say having a melting point higher than 100°C. The reaction preferably takes place at a temperature between 10 and 100⁰C for a time between 1 and 60 minutes. In the next step (b) the microcapsules obtained (whether intact or modified, and independent of the capsular polymer used) are dispersed in a previously prepared emulsion or microemulsion of the synergistic compound. Said emulsion/microemulsion is obtained by mixing, in a suitable solvent, typically water, the synergistic product, a suitable surfactant, possible co-emulsifiers, preservatives, emulsion stabilisers etc, then supplying the necessary energy to the system in accordance with commonly known techniques.

An emulsion is a biphasic system consisting of two insoluble liquids, where one is dispersed within the other in the form of very small droplets of average diameter 0.5-2 micrometres. It is kinetically stable only if suitably formulated. A microemulsion is a clear and thermodynamically stable mixture of at least three components: a hydrophobic component, a surfactant system and water. A microemulsion is a colloidal system in which the insoluble drops are around 10 nanometres in size. The composition of the invention is obtained in which the insecticide-containing microcapsules are dispersed in the emulsion/microemulsion of the synergistic product.

The composition obtained in this manner, once sprayed in vivo, ensures the instantaneous action of the emulsified or microemulsified synergistic compound: it acts immediately on the insect, sensitising it. Then, on exposure to normal environmental factors (air, light, etc.) the microcapsules then disintegrate within a few hours from application: insecticide release therefore takes place on a previously sensitised insect thus increasing the lethal effect of the insecticide. Where the wall is modified, insecticide transfer occurs earlier so partially overlapping with the preceding sensitisation step. In this manner the two steps follow one another more gradually and continuously, avoiding possible treatment interruptions between the two steps. The insect therefore receives an uninterrupted treatment thus reducing the risk of some of the insects moving away before insecticide release.

Finally, where an additional portion of synergistic product is also present inside the microcapsule it functions during the entire insecticide release period, enabling the insects to be continuously sensitised during the entire treatment cycle. Modification of the wall also leads to obvious technological advantages: in this respect, it enables microcapsules to be obtained that are easily erodible in vivo though operating with microcapsules of standard thickness; in this way the use of very thin microcapsules is avoided as they are notoriously difficult to produce. The present invention includes an insecticidal method characterised by the use of the previously described microcapsules.

The invention is described below by means of the following non-limiting examples.

EXPERIMENTAL PART

A. Preparation of microcapsules (method 1)

Example 1 (composition "CH24") 6.7 g of alpha cypermethrin, 6.7 g of piperonyl butoxide and 0.5 g (3.68 mEq) of polymethylene polyphenylisocyanate (PMPPI) are dispersed in water; 30 g of a 4% surfactant solution are added and the mixture is agitated to form an emulsion. A 29 wt% aqueous solution of hexamethylenediamine and an aqueous 30 wt% solution of NH₃ are prepared separately, and the two solutions are mixed in 1 :1 weight proportions; 0.6 g of the resulting solution (corresponding to 3 mEq of hexamethylenediamine and 15.79 mEq of NH₃) are added to the previously formed emulsion of PMPPI and active principles; a further 41.2 g of water are added: the ratio of PMPPI/hexamethylenediamine equivalents in the resulting solution is 1.2: ammonia is present in a quantity greater than the excess of PMPPI.

After a suitable reaction time a microcapsule suspension is obtained. The microcapsules thus obtained contain cypermethrin and PBO and have an average diameter of < 10 micrometres. 6.7 g of the microcapsule dispersion thus obtained are added to a microemulsion containing 16.2 g of PBO prepared separately; water is added to make up to 100 g-

Example 2 (composition "CH37" for comparison) Example 1 is repeated with the only difference being that the 30% NH₃ solution is substituted with distilled water, thus operating in the absence of ammonia. An effective separation of the phases is not achieved and substantial quantities of unencapsulated active principle remain in suspension which interferes with the polymerisation process; stable microcapsules cannot be isolated and it is therefore impossible to proceed with the subsequent step of treatment with microemulsified piperonyl butoxide. Example 3 (composition "CH38" for comparison) 6.7 g of alpha cypermethrin, 6.7 g of piperonyl butoxide and 0.7 g (5.14 mEq) of PMPPI are dispersed in water; 30 g of a 4% surfactant solution are added and the mixture is agitated to form an emulsion. An aqueous solution consisting of 3 parts by weight of 29% hexamethylenediamine and 7 parts by weight of distilled water is prepared separately; 0.6 g of this solution (corresponding to 2.10 mEq of hexamethylenediamine) are withdrawn and added to the previously formed emulsion of PMPPl and active principles; a further 41.2 g of water are added: the ratio of PMPPI/hexamethylenediamine equivalents in the resulting solution is equal to 2.6. Neither ammonia nor other basifiers are present. Negative results are obtained, similar to but of a greater magnitude than those given in example 2. Example 4 (composition "CH39" for comparison) 6.7 g of alpha cypermethrin, 6.7 g of piperonyl butoxide and 0.7 g (5.14 mEq) of PMPPI are dispersed in water; 30 g of a 4% surfactant solution are added and the mixture is agitated to form an emulsion. An aqueous solution consisting of 15 parts by weight of 29% hexamethylenediamine and 85 parts by weight of distilled water are prepared separately; 0.6 g of this solution (corresponding to 1.05 mEq of hexamethylenediamine) are withdrawn and added to the previously formed emulsion of PMPPI and active principles; a further 41.2 g of water are added: the ratio of PMPPI/hexamethylenediamine equivalents in the resulting solution is 3.6. Neither ammonia nor other basifiers are present. Negative results are obtained, being similar to and of a greater magnitude than those given in example 3. The data presented in examples 1 and 2-4 highlight the need to operate with a diisocyanate/diamine ratio of 1.2 in the presence of an amount of monofunctional amine in an equivalent quantity greater than the excess of diisocyanate present. The insecticidal effectiveness of the preparation in example 1 obtained in accordance with the invention is illustrated hereinafter.

8. Preparation of microcapsules (method 2)

Example 5 (composition "CH34") A premix consisting of 41 g technical grade imidacloprid (95% purity), 32.5 g of grinding aids and 256 g of water is prepared. The premix is ground in a micro-ball mill until the average diameter of the particles is less than 10 micrometres. The ground product is placed in a jacketed reactor equipped with a stirrer; urea in the required quantity is added and the required quantity of formaldehyde (a 24% solution) is added to the resulting solution while continuing to stir. The temperature is brought to a value <100°C and hydrochloric acid is added simultaneously as a catalyst. The molar ratio of urea to the active principle to be encapsulated is equal to 1.4:1 ; the molar ratio of formaldehyde to the active principle to be encapsulated is equal to 1.7:1. The temperature is returned to ambient and the reaction is completed.

A microencapsulated product containing imidacloprid is obtained.

5.4 g of the microcapsule dispersion thus obtained is combined with a microemulsion containing 19.3 g of separately prepared PBO; water is added to make up the remainder to 100 g. Example 6 (composition "CH27" for comparison)

The procedure of example 5 is repeated with the only difference being that the molar ratio of urea to formaldehyde to HCI used is 1 :3.1 :3.6.

Example 7 (composition "CH31" for comparison)

The procedure of example 5 is repeated with the only difference being that the molar ratio of urea to formaldehyde to HCI used is 1 :6.3:6.9.

C. Insecticidal activity tests

Example 8

Various concentrations of the polyurea microcapsules obtained in example 1

(composition "CH24" in accordance with the invention) were tested on resistant Q- type whitefly. The percentage mortality was evaluated after 24 hours treatment.

The results are the following: Table 1

Under similar conditions the product CH36 (corresponding to the product CH24, but with traditional polyurea membrane) provided the following results: Table 2

It can be observed that the product CH24 displays a much higher insecticidal activity than CH36 at equal concentrations.

Example 9

Various concentrations of the polyurea microcapsules obtained in example 5, in accordance with the invention, were tested on resistant Q-type whitefly. The percentage mortality was evaluated after 24 hours treatment. The results are the following:

Table 3

Under similar conditions the product of example 6 provided the following results: Table 4

Under similar conditions the product of example 7 provided the following results: Table 5

By comparing table 3 with tables 4 and 5, it can be observed that the products of the invention display a much higher insecticidal activity, highlighted by the lower concentrations needed to obtain high insecticidal effects.

D. NMR analyses

In accordance with the present invention, microcapsules of polyurea containing α- cypermethrin and piperonyl butoxide were prepared from the following mixture:

Technical α-cypermethrin 15% Piperonyl butoxide 15%

Voranate 1.3%

HMDA 29% HMDA: 30% NH₃ 1.6%

Anionic surfactants 4.3% Citric acid 0.5%

Water to 100%

The proton spectrum (Figures 1-2) and that of carbon confirm the presence, in the thus obtained formulated product, of the two active principles (α-cypermethrin and piperonyl butoxide). To evaluate the degree of polymerisation of the capsule wall, the microcapsules were treated with acetone which dissolves the two active principles, leaving the capsular material undissolved.

The residue was then dissolved in DMSO-d₆ and the ¹H-NMR spectrum (fig. 3) and ¹³C-NMR spectrum (Fig. 4) were recorded. The signals at about 1.4 ppm are attributable to the central methylenes of the HMDA residue, those at about 3 ppm to the methylenes adjacent to the urethane groups, those at 3.8 ppm to the

Voranate methylene groups, those at 5.6 ppm to amino hydrogens of the urethane groups, those at 7 ppm to aromatic rings and those at 8 ppm again deriving from urethane NHs. By analysing the aliphatic part of the spectrum (Fig 4), peaks for the 3 methylene groups deriving from HMDA at 25.9, 29.5 and 35.5 ppm can be observed, as can the methylene peak at 38.8 ppm belonging to Voranate.

By analysing the aromatic part of the spectrum, a few urea carbonyl groups (about

156 ppm) can be observed, attributable to the -NHCONH₂ terminal groups deriving from the reaction of isocyanic groups with ammonia.

The peak at 156 ppm confirms the presence of polyurea chains whose formation was interrupted by the polyisocyanate reacting with NH₃. This hence confirms that a capsular wall modified by the partial inhibition of polymerisation was formed.

Claims

1. Process for the formation of a composition with high insecticidal action characterised by the following steps: a) mixing the insecticide with the suitable monomer precursors of a capsular polymer, and polymerising the aforesaid monomers to obtain microcapsules of said polymer containing the insecticide therein, b) mixing the microcapsules obtained in (a) with an emulsion or microemulsion of a synergistic compound.

2. Process as claimed in claim 1 , wherein the capsular polymer is chosen from polyurea, urea-formaldehyde and similar polymers.

3. Process as claimed in claims 1 and 2, wherein the insecticide is chosen from one or more of the compounds of the following classes: pyrethrum, pyrethroids, neonicotinoids, organophosphates, organic acaricides and natural insecticides such as azadirachtin, quassin, rotenone, nicotine, etc.

4. Process as claimed in claims 1-3, wherein the synergistic compound is chosen from piperonyl butoxide, sesamol, verbutin, MGK 264, N,N-diethyl-m-toluamide, Di-n-propyl Isocinchomeronate, citronella, eucalyptus, lemon leaves, peppermint, lavender, cedarwood oil, canola, rosemary, penny royal, cajeput and isoparaffin.

5. Process as claimed in claims 1-4, wherein the mixture undergoing microencapsulation in step (a) also includes an additional portion of synergistic compound to encapsulate together with the insecticide.

6. Process as claimed in claims 1-5, wherein step (a) is carried out under the conditions required to obtain a microcapsule with modified walls.

7. Process as claimed in claim 6, wherein the microcapsule with modified walls is obtained by reacting together an insecticide, a suitable diisocyanate or polyisocyanate, a suitable diamine and a monofunctional amine where the ratio of diisocyanate (or polyisocyanate) equivalents to diamine equivalents is between 1.01 and 1.40, and the monofunctional amine is used in a number of equivalents equal to or greater than the diisocyanate (or polyisocyanate) excess relative to the diamine.

8. Process as claimed in claim 7, wherein the diisocyanate or polyisocyanate is chosen from Diphenylmethane diisocyanate (MDI), Toluene diisocyanate, Isophorone diisocyanate, Diphenylmethane 4,4'-diisocyanate, Hexamethylene diisocyanate, 2-Methyl-1 ,3-phenylene diisocyanate, Methylene diphenyl isocyanate, Hexamethylene-1 ,6-diisocyanate, Polymethylene polyphenyl isocyanate (PAPI), Isophorone diisocyanate (IPDI), 1 ,5-Naphthalene diisocyanate (NDI), Methylene bis(4-cyclohexylisocyanate), aliphatic or aromatic isocyanate prepolymers.

9. Process as claimed in claim 7, where the diamine is chosen from Hexamethylenediamine (HMDA), N-(1-Naphthyl)ethylenediamine, 1 ,2- Phenylenediamine, 4-Aminodiphenylamine, Ethylenediamine, 4-Methyl-1 ,3- phenylenediamine, 4-Methyl~1 ,2-phenylenediamine, 1 ,8-Naphthalenediamine, 4- Nitro-1 ,2-phenylenediamine, 1 ,8-Diaminooctane, 1 ,4-Phenylenediamine, anhydrous Piperazine, 1 ,3-Diaminopropane, 1 ,4-Diaminobutane, 1 ,2- Phenylenediamine, 4-Aminodiphenylamine, 1 ,5-Diamino-2-methylpentane, 1 ,2- Diaminocyclohexane, 1 ,8-Diamino-3,6-dioxaoctane, 2,2- Dimethylpropylenediamine, 1 ,7-Diaminoheptane, 1 ,9-Diaminononane, 2-Nitro-1 ,4- phenylendiamine, 1 ,3-Phenylendiamine, 1 ,2-Diaminopropane, 2-Methyl-1 ,5- diaminopentane, N-Phenylethylenediamine, N-lsopropylethylenediamine, N- Methylethylenediamine, N,N'-Dimethylethylenediamine, toluenediamines.

10. Process as claimed in claim 7, wherein the monofunctional amine is chosen from NH₃, methylamine, dimethylamine, monoethylamine, diethylamine, butylamine, monoethanolamine, diethanolamine, isopropylamine, diisopropylamine, aniline, propanolamine, aminopyridine, cyclohexylamine, dibutylamine, N.N-dimethyltrimethylenediamine, benzylamine.

11. Process as claimed in claims 7-10, wherein the polymerisation reaction between the diisocyanate/polyisocyanate and the diamine takes place at a temperature between 10 and 8O⁰C, for a time between 1 second and 180 seconds.

12. Process as claimed in claim 6, wherein the microcapsule with modified walls is obtained by reacting together the insecticide, urea, formaldehyde and hydrochloric acid in a quantity such that the molar ratio of urea to active principle is between 1.3 and 1.5, preferably 1.4 and the formaldehyde to active principle ratio is between 1.6 and 1.8, preferably 1.7.

13. Process as claimed in claim 12, wherein the molar ratio between urea and active principle is 1.4 and the formaldehyde to active principle ratio is 1.7.

14. Process as claimed in claims 12-13, wherein the polymerisation reaction between urea and formaldehyde takes place at a temperature between 10 and 100⁰C for a time between 1 minute and 60 minutes.

15. Process as claimed in claims 1-14, wherein the average diameter of the obtained microcapsules is between 1 and 500 micrometres.

16. Process as claimed in claims 1-15, wherein the average diameter of the obtained microcapsules is between 5 and 50 micrometres.

17. Composition of high insecticidal activity, obtainable by means of the process described in claims 1-16.