CA1051775A - Insecticidal composition and method of preparing the same - Google Patents

Abstract

A B S T R A C T

A non-poisonous insecticidal composition is disclosed in which inorganic particles such as diatomaceous earth have a sorptive silica gel adhered to the surface thereof. The insecticidal composition is preferably produced by forming the sorptive silica gel in situ in the presence of such inorganic particles.

Description

Insecticides can be generally classified as (1) chemic21 poisons and (2) non poisons. The chemical poisons kill by enterin~l in-to the metabolism of an insect and are in general ~uite ef~ec-tive. It is well recognized however that such poisonous insec-ticides present toxici-ty problems, which, in many cases, have severely limited or precluded their use.
Such toxicity problems have tended to accelerate the development of non-poisonous insec-ticides. Sorptive dusts have shown particular promise for use as non-poisonous insecticides.
Among such materials are various sorptive inorganic materials in-cluding synthetic silicas, tricalcium phospha-te, diatomaceous earths, bentonites, kaolinite clays~ activated carbons, silica aerogels and the like. The effectiveness of such ma-terials as in-secticides r since they are not poisonous, relates -to -the anatomical structure of the insects.
Many common insects have on their bodies a so-called "lipid" layer, which is usually of submicron thickness and is com-posed of a wax or grease like composition roughly analogous to the composition of cornmon beeswax. The lipid layer on an insect is usually found in conjunction with other layers in -the epticuticle of the insect and serves to retain moisture within the insect's body. This type of structure is most commonly found in various arthropods.
Sorptive dusts are believed to function as insecticides by removing or disrupting in some way as by absorption, adsorption or abrasion the lipid layer, thus permitting moisture to escape - from the principal part of an insect's body. Upon such loss of moisture, an insect will normally die.
Many of the sorptive dust type materials indicated in the preceding discussion are not effective enough as insec-ticides to justify their utilization. Certain other of these materials are objectionable for use in certain applications for other reasons such as, for example, because they lower the value of grain con-taining -them. As a result of these considerations and related .'' ~
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fac-t~rs, silica aeroge1 type insecticides are considered to be among t~le most yromising of the sorptive dust insecticides. Insecticides of this type, however, suffer from certain limitations. In general they are too light i~
weigh-t to be satisfactorily employed irl other than enclosed struc~ures. 'I'hey also tend to be too expensive for many applications.
An object of the present invention, therefore, is to provide new and improved compositions serving as sorpt:ive type, non-poisonous insecticides which are more effective than prior related insecticides.
Another object of the present invention is to provide sorptive type insecticidal compositions which may be easily and conveniently manufactured at a comparatively nominal cost.
A further object of the present invention is to provide compositions which may be used easily and conveniently without significant danger.
l'hese and various other objec-ts of this invention will become appar-ent from a reading of the following more detailed description of tne invention.
It can be stated in essentially summary form that the present inven-tion evolves about the discovery that inorganic particles may be coated with an adherent coating of a sorptive silica gel composition, especially hydrogels, and that the particles thus coated are highly effective as insecticides. As will be described more completely, the particles used preferably should have a sorptive surface, that is the particles themselves should be of a sorptive character. Also, for many uses, a compound such as ammonium silico fluoride is preferably included, which is considered to aid in attracting and/or hold-ing the particles to naturally occurring objects including plants and insects.
Accordinglyg the present invention provides a non-poisonous insect-cidal powdered composition useful as a sorptive dust insecticide, effective on contact with the insect's waxy epicute, comprising inorganic sorptive part-icles within the range of from about 100 to about ~00 mesh Tyler screen size and having adhered to the surface thereof a sorptive silica gel, said silica gel constituting at least about 0.1% by weigh~ of the total weight of the coated particles and said composition having a packed bulk density from about 15 to about 100 lbs/feet3.

~ -2-l~S~775 I`he present invention also provides a noll-poisonous insecticidal powdered compositlon ~seful as a sorp-tive dust insecticide, effective on con-tact with the insec~'s waxy eplcute comprising inorganic sorptive particles within the range of from about lO0 to about 400 mesh Tyler screen size and selected from the group consisting of diatomaceous earth, bentonites,sub-ben-tonites, montmorillonites, pyrophyllite, fuller's earth, silica flour, carbon and perlite and having adhered to the surface thereof a sorpti.ve silica gel, said silica gel ranging from about 0.1% to about 10% by weight of the total weight O r the coated particles and said composition having a packed bulk den-sity from about 15 to about 100 lbs/feet3.
In a further embodiment of the present invention there is provided a non-poisonous insecticidal powdered composition useful as a sorptive dust insecticide, effective on contact with the insect waxy epicute, comprising inorganic sorptive particles within the range of from about 100 to about 400 mesh Tyler screen size and having adhered to the surface thereof a sorpti.ve silica gel, said cilica gel being formed in situ in the presence of said inor-ganic particles to adhere to the surface thereof and constituting greater than 0.1% of the total weight of the coated particles and said composition hav-ing a packed bulk density from about 15 to about 100 lbs/feet3.
The preferred particles for use with the present invention are diatomaceous earh (diatomite), since it has been found that such particles are quite effective and also are of comparatively low cost and are readily available. However, various other .

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sor~?tlve materials may b~ used, including ~arous ~en-tonites, sub-bentonit~s, montmorillonites, pyrophyllite, fuller's earths, silica flour, carbon, perlite, and other na-tura] or synthetic sub-stantial equivalents.
The si~e of the inorganic particles can be varied to a considerable extent, although the size of the par~icles is impor-tant with regard to the ease with which the insec-ticide can he distributed. In general, the smaller -the particles the easier it is to distribu-te the particles to an operative or intended location 1~ as long as size of the par-ticle is sufficiently great -that the particles cannot, because of their low weight, be blown about indiscriminately as dust in the air on a normal or "quie-t" day.
Thus, the particles should be sufficien-tly large and/or heavy so that they are capable of settling from "normal" or reasonably quiet air, that is at least about 400 mesh (Tyler screen size) or greater. Because the particles must, however, be sufficiently fine so that they can be easily distributed, they should pass a 100 mesh standard Tyler screen and preferably all or substantially all pass a 200 mesh standard Tyler screen.
In a composition of this invention, the inorganic par-ticles are coated with an adherent coating of a silica gel, normally a hydrogel. Silica aerogels and hydrogels are well known and are used for many purposes such as in the paper and protective coating fields. These aerogels and hydrogels are considered to be highly absorbent for various materials such as wa-ter, oils, waxes, and the like. In general, hydrogels tend to be more absorbent toward water and various compositions which are similar to water than aerogels. Conversely, aerogels tend -to absorh waxes and various other related compounds charac-terized by having compara-tively long aliphatic hydrocarbon chains to à grea-ter extent than ` the hydrogels. It is to be no-ted, however, that the sorptive characteristics of a hydrogel may be changed by various known ex~edients so as to produce properties which -tend -to approxima-te the sorptive properties of an aerogel.

The thickness of the silica gel coating o~ the inorganic particles may be varied considerably and may be either a con-tinuous or discontinuous coating, that is, -the inorganic par-ticles may or may no-t be completely coated. The surface of -the inorganic par-ticles must have sufficient silica gel coated thereon, however, -to impart the necessary sorptive insecticidal properties -to the com-position. Since the lipid layer of insects is very thin, onl~ a small amount of sorptive silica gel is necessary to kill -the in-sects, and hence only a small quanti-ty of silica gel coating on the inorganic par-ticles is necessary. In general, the silica gel coating will be at least 0.1 percent by weight of the -total weight of the coated particles, an~ preferably at least abou-t 0.~ percent.
Insofar as the effectiveness of the insecticidal composition is concerned, there does no-t appear to be an upper limit on the quality of the silica gel coating. For economical reasons, how-ever, the quantity of such coating will be kept to a minimum, generally not exceeding approximately 10 percent by weight of the total weight of the coated particles.
It should also be noted that -the silica gel coated in-~ organic particles, of course, are applied in powder form as a batch of doage of the finely divided coated particles rather than as single particles. Consequently, it is not essential that every particle in such batch have the same quantity of silica gel coating, as it is the effect of the total batch which is significant. In other words, the total batch must contain a sufficient quanti-ty of the sorptive silica gel to provide the necessary insecticidal properties rather than the individual particles. Accordingly, based on the total weight of such a batch, the sorptive silica gel should comprise at least about 0.1 percent by weight and preferably at least 0.2 percent. In this regard, it should also be noted that in some instances, since the insecticidal composition is preferably produced by coating the inorganic particles by :in situ formation of the gel about the par-ticles followed by comminu-tion to provide a composition of reduced particle size, some ~S~7'7~

individual particl~s of the composition may contain little or no silica gel coating. Since ~he coated particles are used as a batch~ however, this will not affect the effectiveness of the composition as an insecticide, so long as the composition as a whole con~ains the indicated minimum quantity of sorptive silica gel.
The composition of coated particles, for effective results, will normally have a packed bulk density of about 15 to about 100 pounds/cubic foot, preferably about 20 to about 30 pounds/cubic foot, since the composition may be used in unenclosed areas where the effect of wind must be taken into consideration~ The packed bulk density, as is well understood by persons skil-led in the art, is the weight/unit volume of the powder when packed in a stand-ard cubic foot container and may be determined simply by filling such a container with the powder and weighing the same.
It has been found that the sorptive silica gel should be intimately adhered to the inorganic particles as a coating rather than in the form of a mixture of the aerogel or hydrogel and such particles since the degree o~
adherence produced by mixing is not sufficient because the silica gel and the inorganic particles may be readily separated as, for example, in handling.
Further, for reasons which are no~ clear, the insec~icide is not as effective as when a direct, intimate bond is achieved between the silica gel and the inorganic particles.
Satisfactory direct coating of the silica gel on the inorganic part-icles in situ, ~hich is generally a preferred method of making the insecticical composition, can be ach;eved by mixing the inorganic particles with a soluble silicate composi~ion in the preparation o~ silica gel as such a gel is being formed. Such gels may be manufactured by various methods, as indicated in United States patents 1,755,496, 2,330,640, 2,625,592, 2,475,253 and 2,477,695.
From a study of these references it will be seen that hydrogels are fre~uently manufactured by treating a solution of a soluble silica compound 3Q such as common water glass with a reagent such as sulphuric acid which changes the pH of the cornpo-sition and causes it to set up as a gel. The particles used in creating an insecticide composition of this invention can be added to such a mixture before or as the reagent or reagents necessary to cause gelation are being added to -t:he soluble silica-te.
In the production of conventional hydrogels, the gel resulting from the mixture of various materials is normally dried and comminuted to a desired size. In the production of an insec-ticide composition of this invention using hydrogel coatings, -the inorganic particles with the gel coating thereon are also normally dried and comminuted. In general, these steps are carried out as in the conventional manufacture of hydrogels, drying at a tempera-ture of from 250 to 350F until completely dry, and then comminu-ting to disintegrate the particles and produce finely divided, discrete coated particles having dimensions corresponding to the dimensions of the uncoated particles employed, i.e., within the range of about 100 to about 400 mesh Tyler screen size.
During the manufacture of the insecticide composition, various secondary type reagents can be added to the reaction mix-

2~ ture, either before a gel forms or at various s-tages during the process of preparing the silica gel coated particles. Thus, for example in accordance with known procedures, compounds such as potassium fluoride or the like may be added to the reaction mixture forming a silica gel in order to increase the pore size of the resultant product.
If desired, the character of the gel prepared in accor-dance with this invention may be altered in other ways. Compounds which are related to soluble silica compounds such as sodium alumi-nate may be added to or mixed with silica compounds during the formation of an insecticidal composition of this inven-tion.
As indicated previously, it is generally preferred to use ammonium silico fluoride to give the Einal composition an electrostatic attrac-tion towards natural objects such as plants, leaves, etc. and insects to aid in air dispersion. The ammonium l r~ ~
silico fluoride can be added to and mixed wi-th -the inorganic par-ticles coated with the sorp-tive silica compound after drying and comminu-ting. When this is done, the resul-tant mixture is dried at a temperature below about 250 F., which is believed -to cause a reaction between -the silica gel and the ammonium silico fluoride to form an electrostatic charge on -the surfaces presen-t.
However, more favorable resul-ts are considered to be achieved by adding ammonium silico fluoride as a wet solution to the gel prior to its being dried at a temperature about 200 F to abou-t 1200 F
in a closed container, venting the water vapor to the atmosphere, and maintaining the ammonium silico fluoride in contact with the coated particle until the temperature is below about 250~Fo As indicated above, it is believed that the ammonium silico fluoride reacts in some manner with the sorptive silica gel to provide the desired electros-tatic properties -to the particles.
Ammonium si~ico fluoride sublimes at about 250F and consequently its presence may not be measurable in the resulting product. Never-theless, the use of such material in production of the insecticidal composition is beneficial and in general, it should be used in a quantity of at least about 5 percent by weight, based on the weight of the sorptive silica gel.
The invention will be better understood by reference to the following specific illustrative examples.
In all of the following examples, the dlatomaceous earth which was used as the inorganic particles was a natural dried and - ground diatomaceous earth, 95 percent by weigh-t of which passed a 325 mesh standard Tyler screen, having a surface area of 25 sq.
meters per gram. For compara-tive purposes, a sample of the sorptive silica gel referred to in each of the examples was also made by -the identical procedure indicated, omitting, however, the inorganic particles.

In each of the examples, the identical procedure was used.
The various materials used in forming the gel were mixed together, allowed to gel or set, washed with water until about 80 percent of the sodium iOIl was removed, ancl then dried and comminuted.
Unless otherwise indica-ted, in each of these examples the pro-duct was ~round -to -325 mesh standard Tyler size, and in all cases after grinding, the composition contained at least about 0.1 weight percent of the sorp-tive silica gel.

Example 1. 46 gms diatomaceous earth, 75 ml. of 40 Be sodium silicate, 1500 ml. water and 25 ml. of a 30 percent by weight aqueous solution of H2SIF6 were mixed and then allowed to set for 30 minu-tes. At the end of -this period, 125 ml. of a 10 percent by weight aqueous ammonia was added.
At the end of 30 minutes, the resultan-t produc-t was washed and filtered. To one-half of this product,0.5 gm amrnonium silico fluoride was added. The part of the product to which this compound was added was then dried at 600 F in a substantially closed container venting the moisture to the atmosphere, and ground. The resultant product contained 61.0 percent by weight diatomaceous earth, with the other 39.0 percent, of course, being the sorptive silica gel.
Exam~le 2. The same procedure and quantities used in the preceding Example 1 were employed except potassium sili-- cate was subs-tituted for sodium silicate. The resultant product contained 61.0 percent by weight diatomaceous earth with -the balance being the sorptive silica.
Example 3. 50 gms of expanded perlite finely ground to 95 percen-t by weigh-t -325 mesh size having a surface area of 20 sq. meters per gram were mixed with 200 ml. water, 50 ml. of an aqueous sodi~n silicate solu-tion having a specific gravity of 1.21, 19 ml. of ~.83 N. KF, and 10 ml. 1.19 specific gravity sulfuric acid. The resultant mixture was allowed to gel, then washed and filtered. This product was -then dr:ied at 600 F

and then ground. The resultant product contained 83 percen-t by weigh-t perlite~ the balance being sorptive silica gel.

Exam~ . 50 gms. diatomaceous ear-th, 200 ml. water, 12. 5 ml. 1. 21 speclfic ~ravity aqueous sodiu~ silica-te solution, 5 ml. 4~83 N.KF`, and 5 ml. 1.19 specific gravity sulfuric acid were mixed. After -the mixture gelled it was washed and filtered, and 2 gm. am~onium silico ~luoride was added. The resul-tant product was dried and -then ground. The resultan-t produc-t con-tained 95 percent by weight diatomaceous earth with -the additio-nal 2 percent being sorptive silica.
Example 5. 50 gms diatomaceous earth, 200 ml. water, 25 ml. 1.21 specific gravity aqueous sodium silicate solution, 10 ml. 4.83 N. KF and 10 ml. 1.19 specific gravity sulfuric acid were mixed. After a gel formed, the resul-tant product was washed and filtered. 2 grams of amrnonium silico fluoride were -then added. The product was then dried at 600 F as in Example 1 and then ground. The resultant product contained 91 percent by weight diatomaceous earth, and the balance, of course, was -the sorptive silica gel.
Example 6. 50 gms. diatomaceous earth, 100 ml. water, 50 mlO 1.21 specific gravity aqueous sodium silicate solution, 19 ml. 4.83 N. KF and 50 ml. 1.19 specific gravity sulfuric acid were mixed. After the mixture gelled, it was washed and filtered and 1.3 gm. of ammonium silico fluoride was added.
The resultant product was next dried at a temperature of 600 F as in Example 1 and then ground. The resultant product con-tained 83 percent by weight diatomaceous earth with the balance being silica gel.
Example 7. 50 gms. diatomaceous earth, 200 ml. water, 100 ml. 1.21 specific gravity aqueous sodium silicate solution, 38 ml. 4.83 N. KF and 100 ml. 1.19 specific gravity sulfuric acid were mixed. After a period of 15 minutes, the product was washed and filtered and 2 gm. of anrmonium silico fluoride was added. Then the resul-tant produc-t contained 71 percent by weight diatomaceous earth with -the balance being sorptive silica gel.

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~5~L7'75 _~mpl~ 8. ~'hc procedure specified ln Exam~le 6 was followed exce~t the prod~ct was dried at 80D F inste2d of ai the temperature indicated. Thc resultant pro~uct co~tained F
83 ~ercent diatom~ccous carth and 17 ~ercent of silica cei.
Example 9. The procedure indicated in Example 6 ~;as followed, but the ~roduct was dried at 350 ~ instead of the temperature indicated. The resultant product contain~d ~3 percent diatomaceous earth and 17 percent ammonium silico fluoride.
Example 10. The procedure indicatcd in E~ample 6 was followed, omi-t-ting the addition of ammonium silico 'luoride.
The resultant product contained 83 percent diatomaceous earth and 17 percent sorptive silica gel.
In order to demonstEate the effectiveness of _he products obtained in accordance with the preceding exam~les, a ,F
serles of tests were run using the inscticide compositions of the preceding examples. Tests were si~ultaneously run utilizing as insecticides the diatomaceous earth and perlite used in the preceding examples and a commercial preparation sold as Dri-Die 67 by the Davison Chemical Company of Baltimore, Maryland. This Dri-Die composition is understood to be a silica aerogel. Also, mixtures of the diatomaceous earth or perlite used in the e~-amples and gels produced in accordance with E~amples 1-7 (omitting the inorganic particles~ were made and tested along with the insecticide compositions of the examples. The physical mixture of these compositions was accomplished by mechanical blending.
In all tests, one-half cc of the insecticidal material bein~ tested was sprinkled as evenly as possible onto the bottom of a 50 ml. ~alss beaker. 10 test insects were then placed on the bottom of each beaker and inspected at periodic intervals.
Th~ test insects were 1'riho1ium confusum l~uval. In the ex-amples, these beetles were r@corded as de~d when there ~as a TRADE ~L9R~

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-total apparen-t lack of physica:L movement of appendages and/or antennae at the time of inspec-lion. In order -to guard against various factors of an extraneous variety influencing the tests, three beakers were used in all tests. The tests were carried ou-t at 50 and 80 percent relative humidity and at a -temperatu:re of 80 F.
The following table indicates the results of these tests.

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From this tahle, it will be seen that the insec-ticide compositions of -this invention are effective for their intended purpose, even at hi~h relative humidity. It will also he ap-parent that the insecticide compositions of -this invention are much more effec-tive than mere mixtures of -the inorganic par-ticles and silica gels. This is considered to be significant and to evidence the presence of a synergistic effect wi-th the insecticides of this inven-tion.
It should also be noted that the insecticide compo-sitions of this invention are comparatively l'heavyl' as compared to previously known sorptive silica compositions and, when ammonium silico fluoride is used, are attracted -to "natural"
objects such as plants or insects so as -to be capable of being used in crop-dusting or the like. Prior related compositions such as the aerogel composition referred to in the table are of such a light and "fluffy" nature that they cannot be employed commercially Eor such purposes.
It is also significant that the insecticide composi-tions of the present invention are of an essentially non-toxic ~0 variety. It is well established that significant quantities of particles such as diatomaceous earth do not harm warm-blooded animals including humans. It is also well established that silica hydrogels and aerogels are of a similar character.
Although no formal toxicity studies are known by us with respect to ammonium silico fluoride, this compound has been previously used in insecticides, and we are not aware of any published reports indicating that it possesses any significant degree of toxicity when used in minor quantities .
It is, of course, to be understood that different in-organic particles and sorp-tive silica compounds could be used in the preceding examples. Similarly, other insects could have been used. For the sake of brevity of disclosure, however~

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such examples are not duplicated herein since the utility and significant contribution of the invention have been demonstra-ted.
From the foregoing it will be apparen-t -that the in-secticides of this invention are non-poisonous, rela-tively ine~-pensive, and effective. It will be apparent that these compo-sitions may be easily and conveniently used in the same manner as other sorptive dust inseetieides for a wide variety of diverse applieations. It will also be apparen-t that the in-seetieide eompositions of this invention may be manufae-tured wi-thout signifieant difficulty at a eomparatively moderate eos-t.

Claims (9)

WE CLAIM:

1. A non-poisonous insecticidal powdered composition useful as a sorptive dust insecticide, effective on contact with the insect's waxy epicute, comprising inorganic sorptive particles within the range of from about 100 to about 400 mesh Tyler screen size and having adhered to the surface thereof a sorptive silica gel, said silica gel constituting at least about 0.1% by weight of the total weight of the coated particles and said composition having a packed bulk density from about 15 to about 100 lbs/feet3.

2. A non-poisonous insecticidal powdered composition useful as a sorptive dust insecticide, effective on contact with the insect's waxy epicute, comprising inorganic sorptive particles within the range of from about 100 to about 400 mesh Tyler screen size and selected from the group consisting of diatomaceous earth, bentonites, sub-bentonites, montmorillonites, pyrophyllite, fuller's earth, silica flour, carbon and perlite and having adhered to the surface thereof a sorptive silica gel, said silica gel ranging from about 0.1% to about 10% by weight of the total weight of the coated particles and said composition having a packed bulk density from about 15 to about 100 lbs/feet3.

3. A non-poisonous insecticidal powdered composition useful as a sorptive dust insecticide, effective on contact with the insect waxy epicute, comprising inorganic sorptive particles within the range of from about 100 to about 400 mesh Tyler screen size and having adhered to the surface thereof a sorptive silica gel, said silica gel being formed in situ in the presence of said inorganic particles to adhere to the surface thereof and constitut-ing greater than 0.1% of the total weight of the coated particles and said composition having a packed bulk density from about 15 to about 100 lbs/feet3.

4. The composition of claim 1 in which said inorganic particles are selected from the group consisting of diatomaceous earth, bentonites, sub-bentonites, montmorillonites, pyrophyllite, fuller's earth, silica flour, carbon and perlite.

5. The composition of claim 1 in which said sorptive silica gel constitutes at least about 0.2 weight percent of the total weight of said composition.

6. The composition of claim 1 in which said sorptive silica gel is a silica hydrogel.

7. The composition of claim 1 in which said composition has a packed bulk density of from about 20 to about 30 pounds/
cubic foot.

8. The composition of claim 1 in which said inorganic particles are diatomaceous earth.

9. The composition of claim 1 in which said composition has a packed bulk density of from about 20 to about 30 pounds/cubic foot.