GB2115282A - Pesticidal composition - Google Patents

Abstract

Pesticidal compositions comprising an insecticidally active sorptive dust, for example a silica or alumaina based amorphous dust, and a synthetic pyrethroid compound of formula: <IMAGE> wherein Q represents a hydrogen atom, or a cyano group; R represents an optionally substituted 2-methylpropyl group 1-substituted by an optionally substituted phenyl or anilino group, or a cyclopropyl group optionally substituted by one or more groups selected from optionally substituted alkyl, alkenyl or cycloalkyl; and each of X and Y independently represents a hydrogen or halogen atom or an optionally fluoro substituted methyl or methoxy group, show mutual potentiation of the components, and are useful as stored grain insecticides.

Description

SPECIFICATION Pesticidal composition The present invention relates to a pesticidal composition comprising an insecticidally active sorptive dust in combination with a synthetic "pyrethroid" insecticide.

It is known that certain mineral dusts show pesticidal activity. Some dusts, for example certain clays, have been used in primitive cultures to protect beans and grain from attack, by admixing the dusts with the food product. Such dusts may be sorptive or abrasive. Thus Ebeling ("Sorptive dusts for pest control" Ann. Rev. Ent. 16123-158(1971)) describes various applications for mineral dusts. Sorptive dusts such as Dridie (trade mark), a silica aerogel, have been used for drywood termite control, and for protecting roof voids from cockroaches and other insects, and in India acid activated Kaolin clay has been used in seed and grain stores.

It has also been known to admix such dusts with pyrethrin and a synergist; one such product Drione (trade mark) comprises DriDie, pyrethrins, synergist and petroleum oil. Ebeling observes that the effect of the pyrethrins in Drione lasts much longer than in most other formulations and states that this is because the pyrethrin, which is known to be very susceptible to degradation by light, is protected from light and air in the pores of the DriDie particles.

When used for protecting stored grain Ebeling (ibid) states that Drione is less effective weight for weight than DriDie, and that this is because the mortality depends on the rate of dessication (which is attributable to the sorptive dust) and not on the toxicant (Pyrethrin), and there is less sorptive dust in the Drione formulation, weight for weight. Such dusts have not become widely used commercially.

In recentyears new "synthetic pyrethroid" insecticides have been developed which are significantly more active than synergised pyrethrins, and are relatively stable to light and air. Such "synthetic pyrethroids" have been suggested for use to control pests in stored grain; thus the "synthetic pyrethroid" permethrin is sold as a wettable powder formulation for use in grain storage, under the trade name "Coopex", and UK Patent Specification No.

1592615 teaches the use of the "synthetic pyrethroid" deltamethrin (decamethrin) in the control of Tribolium castaneum and Sitophllus granarius in stored grain. A conventional pyrethroid synergist may be used in conjunction with the deltamethrin.

It has not however been suggested to combine such "synthetic pyrethroids" insecticides with sorptive dusts. Indeed, since the "synthetic pyrethroid" insecticides are themselves comparatively stable to light and air there is no need for protection of such insecticides as is the objective in the Drione formulation of pyrethrins. Nor would it be anticipated that incorporation of synthetic pyrethroids into soFptive dust formulations such as Drione dust would provide any advantage in the field of grain storage since the literature teaches that the activity of the Drione dust in such applications is principally due to its sorptive characteristics and not to the toxicant (see Ebeling above).

It is therefore surprising and contrary to expectation that, as the Applicants have now discovered, a composition comprising a sorptive insecticidal dust in combination with a "synthetic pyrethroid" insecticide has considerable utility, and in particular enhanced properties over either of the constituents alone.

Accordingly the present invention provides a composition comprising an insecticidally active sorptive mineral dust in combination with an insecticidal "pyrethroid" compound of formula:

wherein Q represents a hydrogen atom, or a cyano group; R represents an optionally substituted 2-methylpropyl group 1-substituted by an optionally substituted phenyl or anilino group, or a cyclopropyl group optionally substituted by one or more groups selected from optionally substituted alkyl, alkenyl or cycloalkyl; and each of X and Y independently represents a hydrogen or halogen atom or an optionally fluoro substituted methyl or methoxy group, for example a trifluoromethyl or difluoromethoxy group.

When R is a phenyl or anilino substituted 2-methylpropyl group the 2-methylpropyl group may be further substituted for example by halogen; preferably however it has no substituents. The phenyl or anilino group may be substituted by halogen atoms, particularly chlorine, or byfluoro- substituted methyl or methoxy groups. Preferably a phenyl group has a single substituent present at the 4-position; and an anilino group is a 2 - chloro - 4 trifluoromethyl anilino group.

When R represents an optionally substituted cyclopropyl group it is preferably substituted, particularly by groups chosen from alkyl, alkenyl and haloalkenyl. Such groups may contain up to 8 carbon atoms. Suitable such groups are methyl, vinyl, halovinyl (particularly 2,2 2,2 - dihalovinyl, for example, 2,2 - dichloro or 2,2 - dibromovinyl), 2 chloro - 2 - trifluoromethylvinyl and dimethylvinyl groups. Especially suitable cyclopropyl groups represented by R are substituted 3,3 - dimethylcyclopropyl groups.

Particularly suitably R is a 1 - phenyl - 2 methylpropyl group in which the phenyl group is substituted at the 4-position by a halogen atom or a fluoromethyl orfluoromethoxy group, particularly a chlorine atom or a difluoromethoxy group, or is a 2 (2,2- dichlorovinyl) - 3,3 - dimethylcyclopropyl, or 2 (2,2 - dibromovinyl) -3,3 - dimethylcyclopropyl group.

Preferably X and Y represent hydrogen atoms.

Particularly suitable compounds of formula I are alpha - cyano - 3 - phenoxybenzyl 2 (2,2 dichlorovinyl) -3,3- dimethylcyclopropanecarboxylate (cypermethrin), alpha - cyano - 3 - phenoxybenzyl 2 - (2,2 - dibromovinyl) - 3,3 - dimethylcyclopropanecarboxylate (deltamethrin), alpha - cyano - 3 - phenoxybenzyl 2 - (4 - chlorophenyl) - 3- methylbu- tanoate (fenvalerate) and 3- phenoxybenzyl 2- (2,2dichlorovinyl) - 3,3 - dimethylcyclopropanecarboxylate (permethrin).

It will he appreciated that compounds offormula I occur in the form of different stereo-isomers, or mixtures of such isomers and formula I is intended to encompass such individual isomers, as well as mixtures of such isomers.

An insecticidally active sorptive mineral dust is a finely powdered mineral which has insecticidal activity in its own right. Generally such dusts are dusts having a large specific surface area, high oil absorption capacity and low bulk density.

The specific surface area of sorptive powders may be measured by a method described as the "BET" (Brunauer, Emmett, Teller) method usually using nitrogen as adsorbate. Using this method with nitrogen adsorbate the specific surface area of suitable sorptive dusts is preferably af least 50 m2/g, more preferably at least 90 m2/g. Suitable dusts have specific surface areas in the range of from 90 to 500 m2/g, and those with a specific surface area of 90 to 250 m2/g have been found to be effective.

Without being bound to such a theory, it is believed that insecticidal sorptive dusts absorb wax from the insect cuticle, leading to dessication of the insect (ller, "Chemistry of Silicas". (Wiley) 1979, p.

752). In some dusts with high specific surface areas measured with nitrogen as adsorbate, it is observed that the inherent insecticidal activity of the powder is very low and it is thought that this results from the size of the pores in the dust being too small to absorb the wax from the insect cuticle. An example of such a dust is Gasil 200 (Joseph Crossfield & Son (see Table I below) ). Accordingly it is not recommended to use dusts having a substantial proportion of their specific surface area associated with pores less than 2nm in size. Preferably the specific surface area is measured by a method which does not include the surface within pores which are too small to absorb wax, for example within pores having an aperture less than 2nm in diameter.

A test which may be used to indicate the capacity of sorptive dusts to absorb wax is the "oil absorption test" (ller, "Chemistry of Silicas", (Wiley) 1979, p.

493). In this test oil is added to a sample of dust. The dust is stirred continuously and when the plasticity point for the dust is reached (the point at which it becomes sticky enough to be rolled into a ball) the amount of oil added is noted. In the tests carried out below, Risella Oil (Registered Trade Mark), was added to 1g of dust. Preferably, according to this test, the sorptive dust absorbs at least 1g oil/g sorptive dust, more preferably at least 29/9. Dusts absorbing at least 2.5g/g of oil have given satisfactory results.

Bulk density may be measured by the method described by Harlow (Ann. App. Biol. 45,90-113 (1957)) in which a vertical tube filled with powder is tapped axially until the volume remains constant, and the density then determined. Suitable dusts usually have a bulk density of less than 0.5 kgllitre.

Particularly suitable dusts have a bulk density up to O.3 kgnitre, for example between 0.05 and 0.15 kgnitre.

The sorptive dust may be any suitable insecticidal sorptive mineral dust. However, when the "pyrethroid compound" is combined with the dust it will generally be adsorbed thereon and clearly it should be capable of being desorbed reasonably easily. The pyrethroid compound should also maintain its insecticidal activity for a suitable length of time, and thus should be substantially stable on the dust, and the dust should not promote premature degradation of the pyrethroid compound. Suitable such dusts may for example be based on silica or alumina. They may be substantially pure or contain a proportion of other elements. Aluminium silicates may be used, and finely divided silica gels or silica powders, colloidal alumina, and finely divided acid activated clays are suitable.Particularly suitable dusts are amorphous mineral dusts especially finely divided silica xerogel, and especially silica aerogels, pyrogenic silicas and precipitated silicas. Preferably such sorptive mineral dusts have a primary partide size ("ultimate" particle size, (see Iler. Page 464 et seq) upto 50nm, for example in the range of from 5 to 30nm, particularly 10 to 20nm, as this type of dust has been found to be very effective.

The surface of such dusts may be treated chemically, for example to make the surface hydrophobic and lipophilic, or both hydrophobic and lipophobic.

Thus fluorinated silica dusts may be suitable, or the silica dust may have a proportion of its hydroxyl groups silated.

Preferably the composition is a pourable, for example a particulate or fluid, composition.

The optimum quantity of pyrethroid compound combined with the sorptive insecticidal mineral dust is dependent on the specific pyrethroid compound as well as the dust used. It is generally recommended that quantities of up to 10% wlw be used, suitably less than 5% w/w, and particularly less than 2%. Good activity has been found when the quantity of adsorbed pyrethroid compound is in the range .01% to 1%. Forthe most active compounds, for example deltamethrin, very good results have been obtained in the range .05 to .5% whir.

It is known that the amount of dust picked up by insects is dependent on the size of the dust, or aggregates of dust, particles, and it is desirable to obtain, when in use, aggregates of an appropriate size. Such factors as the type of dust, the adjuvants to the dust, the mixing processes involved may all affect the final size of the aggregates. In general however it has been found that no special precautions need be taken to ensure suitable aggregate size.

Other adjuvants may suitably be added in some applications. These may for example aid admixture with grain, or restrict formation of dust clouds of the composition. Thus it may be desirable to add quantities of, for example, an inert organic liquid, such as "Risella" oil (Registered Trade Mark), or to add inert solid fillers; preferably such solid fillers act only as diluents and are not picked up by the insect, and should accordingly be fairly coarse or form fairly coarse aggregates. Surfactants which may aid flow or aggregation qualities, or assist in "wetting" may be added. Synergists or other active ingredients, for example other insecticides or fungicides may in certain circumstances be included, as may dyes for example to assist in recognising treated material, or stabilizers.

It has been found that the compositions of the present invention show excellent insecticidal activity, particularly in grain storage, and especially with respect to the flour beetle, Tribolium castaneum.

Accordingly the present invention also provides a method of combatting insects by applying an insecti cidallyeffective amount of a composition according to the invention to a locus infested or liable to infestation by insects, and particularly a method of combatting insects in grain or other dried granular food crop by applying such an amount to the grain, for example by spraying, dusting or other admixture with the grain or part of the grain. Such admixture may be performed by addition to the grain on entry to the silo, or by mixing manually or by machine directly into the grain or by spraying or dusting onto the already stored grain. In common with many other pesticides used in stored grain the activity of the compositions of the invention diminishes at high grain moisture contents.Advantageously the grain moisture content is not more than 15%, particularly less than 14%. Good results have been obtained with grain moisture contents less than 11%. The effect of high grain moisture content may be reduced in some cases by the choice of sorptive dust.

Thus compositions using Aerosil R972 have been found to be more active than those using Cab-O-Sil M5 at high grain moisture content.

The compositions of the invention may be used against many insects, particularly those which are found in or attack stored granular products, such as Sitophilus species (eg Sitophllus oryzae, zeamais or granarius); Rhyzopertha dominica; Trogoderma granarium; Tribolium castaneum, Tribolium confusum, Oryzaephilus surinamensis, Oryzaephilus mercator, Cryptolestes pusillus and Ephestia species. The compositions of the invention have given very good results with Sitophllus granarius, Oryzaephilus surinamensis, Cryptolestes pusfilus and Tribolium confusum.

The composition of the invention has been found to be particularly effective against flour beetles, Tribolium castaneum, and accordingly the method is very suitable for treatment of grain infested with such beetles.

The rate of application of the composition of the invention will depend on many factors, for example the pyrethroid compound used, the sorptive dust used, and the application desired, and the species of insect it is desired to combat. In grain storage the application rates are generally in the range 10 to 500 gitonne of grain, particularly lOto 200 gitonne of grain. Suitable control has been achieved in tests using from 10 to 100 g/tonne of the composition, for example amounts in the range 15 to Sogitonne.

It will be appreciated that at these levels of control the application rate of the pyrethroid compound is very low. Thus for deltamethrin and pyrethroid compounds of comparable inherently high insecticidal activity the rate of application of the pyrethroid compound is conveniently in the range from .0025 to lgltonne (grain). In tests, amounts in the range .005 to .1/tone, particularly .01 to .05gltonne, have given good results.

For permethrin and cypermethrin and similarly active pyrethroid compounds the rate of application of the pyrethroid compound is conveniently in the range from .005 to Sg/tonne. Good results have been obtained in tests with amounts in the range from .025 to 1 g/tonne, particularly from .05 to .Sgltonne.

The present invention further provides a method of preparing a composition according to the present invention which comprises dissolving the synthetic pyrethroid compound of formula I in a suitable solvent, and admixing the solution with the sorptive mineral dust Suitable solvents may be any inert organic solvent capable of dissolving an appropriate quantity of the pyrethroid compound. Hydrocarbon solvents may be used, for example C5-C8 alkanes, such as n-hexane, or polar organic solvents for example alcohols or ketones, such as acetone.

The amount of solvent used per gram of sorptive dust will depend on the nature of the dust, and in particular its oil absorption capacity. In general the amountwill lie in the range of from 10 O to 100 ml/g sorptive dust, for example from 15to 50 ml/g. Good results have been obtained with 20 ml/g solvents sorptive dust.

The invention is further illustrated by the following examples.

Examples I, II, VI and VII show the insecticidal activity of the dusts and pyrethroid compounds independently, and Examples Ill, IV, V, Vlil and IX illustrate compositions according to the invention. In these examples LC50,s were determined from bioassay data using the loglprobittransformation and a maximum likelihood technique for fitting a straight line to the data. The LC95 values were extrapolated from the LC50 values and the slope of the fitted line and in many cases these LCSdS have a wide confidence interval.

Example I Insecticidal activity ofsorptive dusts against Tribolium castaneum in wheat Wheat samples (1009) (10-11% moisture content) were weighed into 500ml lidded jars. The required inert dust concentrations were weighed and added to the wheat samples. Each jar was covered and tilted up and down for 5 seconds (6 times) and hand rotated for 3 minutes with shaking at the following time intervals: 10 seconds, 15 seconds, 30 seconds, 1 minute, 11/2 minutes and 2 minutes. After admixing, the jars were kept closed until the dust inside had settled.

T. Castaneum (50) were introduced into each jar which was then sealed with filter paper at 26"C.

Mortality counts were made at the end of 48 hours.

Insects were classified~as dead or alive, dead insects being defined as those that showed nb visible movement after 20 seconds observation. All the tests were done in replicates of two. From these tests the LC50's and LC95's for the mineral dusts shown below were calculated (Finney 1971, "Probit Analysis" 3rd edition, Cambridge Univ. Press), and the results are set out in Table 1. This Table also includes the specific surface area, bulk density, and oil absorption capacity of the dusts. The dusts Gasil 200, Talc, Montmorillonite and Bentonite are included for comparison, and are not active under the bioassay conditions used and not used in compositions according to the invention.

Table I

Dust1 Dust7 Specific Oil Absorption Bulk LC508 extrapolated8 Type Surface Capacity (g Density (10 g/g LC95 (10-6 Area (m/g) Risella Oil/g (g/l) wheat) g/g wheat) dust) Aerosil R972 FS 120 2.5 50 111 198 Cab-O-Si1 M5 FS 200 4.4 50 129 244 Cab-O-Si1 M5 (2) FS - - 130 134 226 Cab-O-Si1 EH5 (6) FS 390 5.1 50 128 224 Cab-O-Si1 H5 (6) FS 325 4.6 40 104 283 Cab-O-Sil MTD (6) FS 200 4.4 130 142 231 Wacker HDKH20 (6) FS 170 3.5 60 97 240 Wacker HDKH2O (6) FS 200 4.6 40 104 252 Wacker HDKH2F (6) FS 120 1.7 240 126 186 /essalon S PS 190 3.3 120 138 - 22T Silica N320 PS 230 2.5 180 203 320 Aluminium PS 100 1.5 290 338 655 Silicate P820 Gasil 35 | PS 326 2.5 160 186 334 Gasil 230 PS 290 3.6 120 128 214 Gasil 200 (5) PS 750 0.8 430 - Table I continued........

Dustl Dust7 Specific Oil Absorption puua LC5 8 extrapolated Type Surface Capacity (g Density (10-6 g/g LC95 (10-6 Area (m/g) Risella Oil/g (g/l) wheat) g/g wheat) dust) Talc (5) NC 0.74 0.4 960 - Montmorillonite (5) NC - 0.4 1070 - Bentonite (5) NC - 0.5 950 - Notes to Table I 1.The dusts were obtained from the following sources: "Gasil", Joseph Crossfield & Sons Ltd; "Cab-O-Sil", Cabot Carbon Ltd; "HDK", Greef Chemicals Ltd; "Aerosil", "Wessalon", "Alumi nium Silicate P820","Silica K320", Bush Beach & BR< Segner Bayley Ltd. (These names are trade marks). The natural clays were obtained from B.D.H. Ltd.

2. Pretreated with hexane and dried under vacuum.

3. Manufacturers' quotation.

4. As determined by Harlow, Ann. of App. Biol. 45 90-113(1957).

5. These dusts are examples of dusts which are not insecticidally active and accordingly are not suit able in compositions according to the invention.

6. The LC50's and LC95,s of these dusts were estab lished on a more susceptible population of Tribo lium cataneum (LC50 Cab-O-Sil M5=59.4x10-5, LC95 = 105 x 10-6 9/9 wheat) and the LC's and LC96's have been normalised to make them consistent with the other dusts in the table.

7. Dust types: FS = fumed or pyrogenic silica PS = precipitated silica (xerogel or aerogel) NC = natural clay.

8. LC50's determined from bioassay data using the loglprobittransformation and a maximum likelihood technique for fitting a straight line to the data. The LC95 values were extrapolated from the LC50 values and the slope of the fitted line and in many cases these LC95's have a wide confidence interval.

Example II Insecticidal activity of pyrethroid compounds Formulations of the pyrethroid compounds on an inert carrier, talc (talc is insecticidally inactive under the bioassay conditions described), were prepared by dissolving the pyrethroid compound in 4ml (per gram of talc) of a suitable solvent and slowly adding the solution to the talc with constant stirring to give a slurry. This was allowed to dry for 48 hours in the dark, and then transferred to a stoppered glass bottle and shaken to distribute the dust particles randomly.

Wheat samples (1009 at 10 to 11% moisture content) in 500ml jars were admixed with 4 or 5 pyrethroid concentrations (% by weight) for each formulation. T. castaneum (50) were introduced and the jars were incubated at 26 C. Percentage mortality was recorded at the end of the bioassay period. In the assessment of percentage mortality, insects were classified into three categories: alive, dead and "knocked-down". Dead insects were those that showed no visible movement after 20 seconds observation period; insects that showed visible movements but failed to walk (i.e. which turned over and lay on their backs when placed on their feet) on a filter paper after 20 seconds, were counted as "knocked-down"; those which could walk were counted as alive. Tests were done in replicates of two.In the 2 day bioassay period used "knocked-down" insects were classified as alive, because most, after removal from the wheat, recovered.

The insecticidal efficacy of the formulations was determined over a 2-day period. From these tests the LCSO's and LC95's of the pyrethroid compounds were determined and are shown in Table II below.

TABLE II Insecticidal Activity of pyrethroid compounds (2 day bioassay) Pyrethroid Pyrethroid on LC50 Lc95 compound talc conc. (% w/w) 10-6g(pyrethroid/ g(dust) Permethrin 2.51 58.73 170.1 Cypermethrin 2.54 36.80 981.6 Deltamettrin 7.55 - 20.20 66.7 Insects exposed to concentrations of less than 1% wlw (pyrethroid on talc) were knocked down, but all recovered after 48 hours bioassay.

Example III Activity of compositions according to the invention In this Example each pyrethroid compound was dissolved in 20ml/g (dust) of suitable solvent (hexane (bp 60 -80 C) for permethrin and cypermethrin; acetone for deltamethrin). The solution was added to the dust with constant stirring to give a slurry which was kept in the dark for 24 hours, broken into smaller pieces and dried on a filter paper for a further 24 hours. The pieces were then crushed gently, transferred to a stoppered bottle and shaken to distribute the particles randomly.Compositions containing varying amounts of pyrethroid per gram dust were prepared and the insecticidal efficacy of the compositions was determined over a 2 day bioassay period as described in Example II. (For the 48 hour bioassay period insects which were observed as "knocked down" were classed as "alive", as most of them recovered if left). From these test results the LC50's and LC85,s of the compositions were calculated and these results are set out below in Tables Ill-VIll. In these tables the pyrethroid/dust concentration is given in mg(pyrethroid) / g(dust), and the LC50's and LC95's in microgramme (formulation) I (wheat).

TABLE III (Permethrin/Cab-O-Sil M5) Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g (dust)) 10-6g(formulation)/g(wheat) 1.00 50.8 125.4 5.00 20.7 38.97 11.92 27.7 142.0 22.73 92.1 195.4 32.89 132.6 292.7 52.10 140.2 323.9 73.72 149.5 299.0 100.72 153.0 288.9 TABLE IV (Permethrin/Aerosil R972) Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 1.00 59.7 103.7 2.50 34.9 61.8 5.00 33.9 51.8 10.00 84.5 418.6 15.00 130.6 520.8 20.00 184.4 544.1 TABLE V (Cypermethrin/Cab-O-Sil M5) Pyrethroid concentration to50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.50 50.7 77.9 1.00 25.7 42.9 5.00 45.3 417.6 10.00 93.2 171.4 21.52 121.5 ' 237.6 51.25 189.9 704.6 100.80 275.6 954.4 TABLE VI (Cypermethrin/Aerosil R972) Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.20 57.7 95.34 0.50 35.3 55.16 1.00 26.2 42.49 5.00 42.2 169.1 10.00 ~ 71.5 170.3 15.00 109.6 312.9 20.00 137.8 357.6 TABLE VII (Deltamethrin/Cab-O-Sil M5) Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.10 56.9 95.4 0.25 35.8 64.00 0.50 29.4 76.3 2.50 91.4 232.7 5.00 120.2 336.3 10.00 195.9 686.9 TABLE VIII (Deltamethrin/Aerosil R972) Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.10 31.4 50.2 0.20 26.7 43.7 0.50 19.8 42.2 1.00 39.9 80.6 5.00 82.8 193.1 7.50 153.9 576.3 A number called the coefficient of cotoxicity provides an indication of the degree of potentiation between the pyrethroid compounds and the sorptive dust. The coefficient of cotoxicity (see Sun and Johnson (J. Econ. Ent. 53(1960)887-892)) is the ratio of the theoretical LC50 assuming additive action to the actual LC50 of each of the compositions xl 00.

A coefficient of cotoxicity in excess of TOO evidences a degree of potentiation (more than additive action) between two components. Table IX below sets out the coefficient of cotoxicity of the compositions in Table Ill to VIII above. In each case the coefficient of cotoxicity is calculated at the value of the LC50 which gives a maximum coefficient of cotoxicity. (The "optimum LC50"). In addition the LC50's of the individual components are included in the table for comparison.

TABLE IX (Coefficients of Cotoxicity) Active material Pyrethroid K Sorptive dost Coefficient concentration coneentration of Cotoxicity at LC50 at LC50 Permethrin 58.73 - Cypermetbrin 36.80 - Deltamethrin 20.20 - - Cab-O-Sil M5 - 129 Aerosil R972 - 111 Composition of Table No.

III .10 20.6 620 IV .17 33.7 325 V .026 25.7 500 VI .026 26.2 420 VII .015 29.4 440 VIII .010 19.8 560 * concentration of pyrethroid oF dust in microgram/g (wheat) at its individual LC50, or at the optimum LC50 for compositions of the invention.

From the coefficients of cotoxicity for the compositions of the invention it can be seen that there is a very significant degree of potentiation between the pyrethroid compound and the sorptive dust.

It may be noted from Tables III to VIII that at high pyrethroid concentrations the LC50 appears to rise rapidly. It is believed that this is a result of the rapid knockdown effect of the pyrethroid disabling the insect which is then unable to pick up further dust, and which after contact for 48 hours may survive.

However, after longer contact periods, for example 7 days, (illustrated in Example VIII, Tables XIII to XV) the insects do not survive, and the LC50 decreases with increasin pyrethroid content.

Example IV Activity ofcompositions according to the invention including various quanti ties ofan organic liquid Formulations containing various quantities of Risella Oil and 0.5% whN permethrin on Cab-O-Sil M5 were made as follows: A solution containing 9.87 mg of permethrin (94% a.i., cis/trans isomeric ratio 22.3:77.7) in hexane (10 ml) was prepared, and a volume (5.2 ml) was pipetted into a beaker (100 ml). To this was added 5 mg of Risella Oil dissolved in 10 ml hexane. The two solutions were thoroughly mixed and the volume made up to approximately 20 ml with hexane. This mixture was added slowly to lg Cab-O-Sil M5 to give a slurry which was treated in the same way as described in Example Ill.

Similarly, formulations containing 5 mg of per methrin (based on 97% a.i.) plus 15,45 and 95 mg Risella Oil to ig Cab-O-Sil M5 were prepared.

The effectiveness of the formulations were assessed over a 2-day period as described in Example II.

The LC50's of the formulations were calculated and are shown in Table X below.

TABLE X (Permethrin/Cab-O-Sil M5/Eisella Oil fomulation) Risella Oil Concentration LC50 LC95 (mg per g formulation 10 g (formulation)/g(wheat) (Permethrin/Cab-O-Sil MS 0.5% w/w)) 0.00 20.7 39.0 5.00 33.6 79.1 15.00 43.1 72.1 45.00 47.8 69.6 95.00 46.7 64.2 From these results it can be seen that inclusion of Risella Oil slightly reduces the effectiveness of the compositions, but that the compositions nevertheless show significantly enhanced activity over the individual components.

Example V Residual toxicity of composition according to the invention The residual efficacy of deltamethrin/ Cab-O-Sit M5 (0.Smglg) on wheat was monitored over a 5 month period at monthly intervals on wheat of moisture contents of 12 and 9% respectively.

Wheat samples (100 g) in 500 ml lidded jars were admixed with 48 hour LC95 concentration calculated for the formulation against T. castaneum as in Example III. The jars were tightly sealed and kept at 26 C over potassium hydroxide solutions in equilibrium with the relative humidities corresponding to their moisture content. At monthly intervals T.

castaneum (50) were introduced and the jars were sealed with filter paper and reincubated. Percentage mortality of T. castaneum and moisture content of the wheat samples were estimated after 48 hours.

Two replicates were carried out for each moisture content at monthly intervals.

The percentage mortality of the Tribolium castaneum after a given number of months in each test is set out in Table Xl below.

TABlE XI Percentage Mortality After Time (Months) S Moisture Content of Wheat O 1 2 3 4 5 100 100 100 94 98 100 100 100 100 96 100 96 Mean 100 100 100 95 99 98 100 100 98 88 98 98 12.4 100 100 100 100 98 98 Mean 100 100 99 99 98 98 It can be seen from these results that the composition comprising deltamethrin and Cab-O-Sil M5 has excellent long term activity in combatting Tribolium.

Example VI The insecticidal efficacy of Cab-O-Sil M5 was determined as described in Example I but using a 7 day bioassay period. From this test the 7 day LCS0 and LC95 were calculated to be: 7 day LC50 52.7 microgramme/g (wheat) LC95 93.6 microgramme/g(wheat) Example VII The insecticidal efficacy of several pyrethroid compounds was determined as described in Example II, but using a 7 day bioassay period ("knocked down" insects were classified as dead in this test (see Example VIII)). Table XII below gives the concentration of pyrethroid (% w/w on talc) and the calculated LC80,s and LCgs's.

TABLE XII Insecticidal activity of pyrethroid compounds (7 day biosaaay) Pyrethroid Pyrethroid on LC50 1095 compound tale conc. (%v/w) 10 g(pVrethroid)/ g(wheat ) Permethrin 2.04 4.86 13.2 Permethrin 0.50 4.86 17.3 Permethrin 0.10 5.35 17.1 Cypermethrin 2.00 0.233 0.69 Deltamethrin 0.23 0.078 0.18 Several concentrations of permethrin on talc were used, and in each case the LC50 and LC95 was approximately the same indicating that there is no significant potentiation between pyrethroid and talc.

Example VIII Insecticidal efficacy of compositions according to the invention over 7 day bioassay period The insecticidal efficacy of compositions containing varying amounts of pyrethroid per gram of dust was determined as described in Example Ill, but over a 7 day bioassay period. In this test the "knockeddown" insects were classified as dead as most of them died within 24 hours of following removal from the treated wheat. From these test results the LC50,s and LC95,s of the compositions were calculated and these are shown in Tables XIII to XV. In these tables the pyrethroid/dust concentration is given in mg (pyrethroid)/g (wheat). The coefficients of cotoxicity for these compositions were also calculated as described in Example III, and are set out in Table XVI.

TABLE XIII (Permethrin/Cab-O-Sil M5) - 7 day bioassay Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.50 - 50.4 93.4 1.00 - 37.0 86.4 2.00 29.6 50.3 5.00 18.4 36.6 10.00 15.7 31.8 20.00 111.5 31.6 TABLE XIV (Cypermethrin/Cab-O-Sil M5) - 7 day bioassay) Pyrethroid concetration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.10 41.5 72.1 o.50 36.2 80.5 1.00 21.0 51.8 5.00 14.7 28.6 10.00 11.0 23.3 20.00 7.84 19.6 TABLE XV (Deltamethrin/Cab-O-Sil M5) - 7 day bioassay Pyrethroid concentration LC50 LC95 (mg(pyrethroid)/g(dust)) 10-6g(formulation)/g(wheat) 0.05 31.5 61.8 0.10 21.1 45.7 0.20 16.1 29.3 0.50 13.6 24.2 1.00 7.45 17.6 2.00 5.75 16.3 TABLE XVI (Coefficients of cotoxicity - 7 day bioassay) Active Pyrethroid Conc. Sorptive Dust Coefficient Ingredient at LC50* Conc. at LC50* Cotoxicity permetbrim 48.6 cypermethrin 0.233 deltamethrin 0 .o78 Cal-O-Sil M5 - 53.7 Composition of Table No.

XIII 0.28 14.2 370 XIV 0.021 2I.0 210 XV 0.0075 7.5 420 * Concentration of pyrethroid or dust in microgram g wheat at individual LC50 or at optimum LC50 of composition.

From the coefficients of cotoxicity for the composi tions of the invention it can be seen that there is a very significant degree of potentiation between the pyrethroid compound and the sorptive dust.

This is also illustrated by the isobologram for the joint action between the pyrethroid compound and sorptive dust. (isobolograms are graphical plots of the concentration of one component in a formulation against the other component (in a two component formulation) at the LC50 of the formulation. The line joining the LC50's of each component alone repre sents additive action. and any deviation inwards from that line indicates some degree of joint action.

In the Figure the LC's of the sorptive mineral dust, and the synthetic pyrethroids have been normalised so that each appears on the scale at the point marked 1.0. The Figure shows isobologramsforthe three compositions in Tables XIII to XV from which it can be seen that there is very significant potentiation.

Example IX Effect of wheat moisture content on activity of compositions of fhe inven tion Wheat grain (13.7% moisture content) was con ditionedtogive moisture contents of 9, 11,16 and 18% by addition of water or- drying as appropriate.

After treatment the moisture content was deter mined by grinding the wheat and drying in an oven for for 30-60 min) and comparing the dry weight with the wet weight.

Conditioned wheat was admixed with the com position as described in Example Ill, using the calculated LC95 amounts, 50 Tribolium castaneum were added, and the jars sealed and incubated at 26 C at an appropriate relative humidity.

Percentage mortality was recorded at 2 day intervals for 10 days; after each count the wheat and composition was replaced in the jar and further mixed,and the insects which were not dead reintro duced.

The percentage mortality at different moisture contents for a permethrin/Cab-O-Sil A (5mg/g) formulation and permethrinlAerosil R972 (5mg/g} formulation are shown in Tables XVII and XVIII below.

In each case two replicates were carried out and the result is the mean of these.

TABLE XVII (Permethrin/Cab-O-Sil M5 (5 mg/g)) % Mortality after Days Moisture Content of Wheat (,%) 2 4 6 8 10 9.5 95 100 100 100 100 10.4 78 84 88 88 88 13.4 66 67 67 67 67 15.9 9 9 9 9 9 17.7 1 1 1 1 1 TABLE XVIII (Permethrin/Aerosil Sag72 (5 mg/g)) Moisture Content % Mortality after Days of Wheat (%) 2 4 6 8 10 9.2 99 100 100 100 100 11.4 85 100 100 100 100 13.3 66 89 94 94 94 15.1 40 63 63 63 63 17.0 11 18 18 18 18

Claims (18)

1. A pesticidal composition comprising an insecticidally active sorptive mineral dust in combination with an insecticidal synthetic pyrethroid compound of formula:

wherein Q represents a hydrogen atom, or a cyano group; R represents an optionally substituted 2-methylpropyl group 1-substituted by an optionally substituted phenyl or anilino group, or a cyclopropyl group optionally substituted by one or more groups selected from optionally substituted alkyl, alkenyl or cycloalkyl; and each of X and Y independently represents a hydrogen or halogen atom or an optionallyfluoro substituted methyl or methoxy group.

2. A composition according to claim 1 wherein the sorptive dust has a specific surface area of at least 50m2/g.

3. A composition according to claim 2 wherein the sorptive dust has a specific surface area of at least 90m2/g.

4. Acomposition according to claim 2 or3 wherein the specific surface area is measured by a method which does not include the surface within pores having an aperture less than 2nm in diameter.

5. A composition according to claim 1, 2,3 or 4 wherein the sorptive dust has an oil absorbtion capacity of at least 1 g oil/g dust.

6. A composition according to any of the preceding claims wherein the bulk density of the sorptive dust is up to 0.3kg/litre.

7. A composition according to any of the preceding claims wherein the sorptive mineral dust is an amorphous mineral dust.

8. A composition according to any of the preceding claims wherein the sorptive dust is a dust based on silica or alumina.

9. A composition according to claim 8 wherein the sorptive dust is a finely divided silica xerogel, or aerogel, a pyrogenic silica, or a precipitated silica.

10. A composition according to any of the preceding claims wherein in the synthetic pyrethroid compound offormula I, R is a 1 - phenyl - 2 methylpropyl group in which the phenyl group is 4-substituted by a halogen atom or a fluoromethyl or fluoromethoxy group, or R is a 2 - (2,2 - dihalovinyl) - 3,3 - dimethylcyclopropyl group.

11. A composition according to any of the preceding claims wherein, in formula I in claim 1, X and Y are both hydrogen.

12. A composition according to claim 11 wherein the synthetic pyrethroid compound is alpha - cyano 3 - phenoxybenzyl 2 - (2,2 - dichlorovinyl) - 3,3dimethylcyclopropane carboxylate, alpha - cyano - 3 - phenoxybenzyl 2- (2,2 - dibromovinyl) - 3,3 dimethylcyclopropanecarboxylate, alpha - cyano - 3 - phenoxybenzyl 2 - (4 - chlorophenyl) - 3 - methylbutanoate, or 3 - phenoxybenzyl 2 - (2,2 - dichlorovinyl) - 3,3 - dimethylcyclopropane carboxylate.

13. A composition according to any of the preceding claims wherein the quantity of synthetic pyrethroid compound is less than 2% w of the composition.

14. A process for the preparation of a composition according to any of the preceding claims wherein the synthetic pyrethroid compound of formula I is dissolved in a solvent, and the solution is admixed with the sorptive mineral dust.

15. A method of combatting insects by applying to a locus infested or liable to infestation by insects an insecticidally effective amount of a composition according to any of claims 1 to 13.

16. A method according to claim 15 wherein the composition is applied to grain or other stored granular food crop.

17. A method according to claim 15 or 16 for combatting Tribolium castaneum.

18. A composition as claimed in any of claims 1 to 13 as hereinbefore described with specific reference to any one of Examples lil to V and VIII or IX.