CA1268114A - Insecticide composition for controlling insects which have an aquatic breeding site - Google Patents

Abstract

24 An insecticide composition for controlling insects that have an aquatic breeding site, such as mosquitoes, is provided. The composition comprises a first component which is capable of forming either an insoluble monomolecular layer, an insoluble foam layer or a duplex film layer on the surface of a water catchment and a second component which has a toxic action on larvae giving rise to a synergistic mixture.

Description

-page 1-BREEDING SITE

This invention relates to insecticide compositions for controlling the breeding of insects which have aquatic breeding sites.
In the specification of our Patents Nos.1 357 952 (March 1971) and 1 557 804 (0ct 1976) there is disclosed a method of controlling the breeding of mosquitoes by forming an insoluble monomolecular layer on the surface of water to reduce the number of mosquito pupae and larvae.
The monomolecular layer is particularly effective in killing the mosquito at certain stages of the life cycle, namely the ovipositing female, fourth stage larva, pupa and emerging adult. It is lethal because the decrease in surface tension causes wetting of the respiratory trumpets of the pupae and larvae and also forms a physical barrier to surface penetration, thus preventing oxygen uptake from the atmosphere by the larvae and pupae. The application of monolayers to the control of mosquito juveniles is described in:
1. McMullen, A.I. & Hill, M.N., (1971), Nature, 234 , No.5323 pp51-52.

2. McMullen, A.I., Reiter, P. & Phillips, M.C., (1977), Nature, 267 , No.5608 pp244-245.

3. Garrett, W.D., (1976), Naval Res. Lab. Report 8020, pl3, Washington D.C.
In the specification of our Patent No. 1 561 088 there is disclosed a method of controlling the breeding of insects which have an aquatic phase in their life cycle by forming an insoluble foam layer on the surface of the water. This foam layer presents an impenetrable barrier to pupae and larvae of the insects, again wetting their ~ 6~114 -page ~-respiratory system and preventing oxygen uptake.The foam method is more effective than the monomolecular method in that it is effective in killing the mosquito at all stages in its life cycleS namely: ovipositing female, egg, first, second, third and fourth stage larva, pupa and emerging adult. It is, however, more expensive than the monomolecular method in both dosage and application equipment.
There are also specific toxins obtained from Bacillus thurin~iensis cultures (hereinafter referred to as B.t.) and from Bacillus sphaericus cultures which are mainly effective against first, second and third stage mosquito larvae but suffer from the disadvantage that the toxin crystal is dense and rapidly sinks below the feeding zones of young larvae. It is also rapidly inactivated by particulate matter in the catchment.
It has unexpectedly been found that by mixing the toxin from Bacillus thurin~iensis or Bacillus sphaericus with the material forming the monomolecular layer, the toxin is retained at the surface for quite long periods and is transported or spread over wide areas. When the toxin is mixed with an insoluble foam layer the toxin is held at the surface for periods depending on the speed of breakdown of the foam, which depends on the amount applied and the extent of water pollution.
Alternatively, the monomolecular layer and toxin mixture can be applied to the water surface with a thin oil layer applied on top thereof, thus forming a "duplex film". These methods of applying the toxin to a water catchment result in a much more effective method for killing mosquitoes than by applying the monolayer, foam, thin oil or the toxin alone. Thus the combination produces a syner~istic mixed product.
According to the present invention there is provided an insecticide . 1;~6E3114 -page 3-composition for controlling insects which have an aquatic breeding site comprising a first component which is capable of forming either a monomolecular layer, an insoluble foam layer or a duplex film layer on the surface of a water catchment and a second component which has a toxin action (preferably rapid) on larvae, giving rise to a synergistic mixture.
To improve the retention of the toxin by the monomolecular material, preferably a gelling agent or viscosity modifier is added to the composition. Figure 1 shows the sedimentation boundary of the B.t.
suspension in a preferred monolayer with a gelling agent at a preferred concentration.
The first component of a composition in accordance with this invention may be any one or more of the compounds referred to in the specification of Patents Nos. 1 557 804 and 1 561 088. Thus the first component may include at least one long chain compound of the general formula:

C H .(OR) OH or C H .(OR.OB) OH
m 2m + 1 n m 2m + 1 n and/or at least one long chain compound of the general formula:
C H .CO.(OR) OH or C H .CO.(OR.OB) OH
m 2m + 1 n m 2m + 1 n where these include branched chain isomers, e.g.:
CH

>CH.(CH ) ... etc., In these formulae R and B are alkylenes and may be the same or different, n is an integer in the range 1 to 3 and m is an integer greater than 14.
Such a compound is capable of forming an insoluble monomolecular `` ~681~4 -page 4-layer, a foam layer or, (in the presence of an oil), a duplex film, on the surface of a water catchment.
Preferably, the first component comprises a mixture of cetyl, stearyl and oleyl mono- or di-ethoxylates.
The second component may be any specific mosquito larval toxin such as that obtained during growth of bacterial cultures, for example, that toxin found in B. thurin~iensis H-14 (Bt-H14) or in B. sphaericus preparations, the toxin being a high molecular weight protein which splits into active sub-units inside the larvae.
The toxin from Bt-H14 can readily be produced by deep-liquid fermentation using for example the method described by Nickerson, K.W.
and Bulla, L.A., App. Microbiol. , (1974), 28 , ppl24-128.
This produces an aqueous dispersion whose toxin content depends on a number of variables. However, an arbitrary and comparative standard, assessed by bioassay, of about 1000 International Units per mg. is aimed for.
Methods for obtaining compounds suitable for the first component are described in British Patent Specification Nos. 1 557 804 and 1 561 088.
The components of the insecticide composition may be formulated for application to water in several ways.
1) Monomolecular Layer Formulation A) Where the first component is in the form of a hydrophobic soft wax or "oil" at ambient temperatures and the second component is in a dehydrated, spray-dried or freeze-dried solid form (produced from the aqueous dispersion obtained from fermentation as described above) the two components are mixed in the desired preparations as 100% "active ingredients" and applied directly to the water surface.
B) When the first component may be solid or semi-solid, it may be ~ 268ii4 -psge 5-prepared by gradually adding it to water being stirred vigorously in a high speed mixer, emulsifier or colloid mill to form a dispersion having a concentration of from 10% to 20% w/v. This preparation may be mixed directly with a dispersion in water of the second component, the two being mixed to the required content of each ingredient.
C) Where the first component is in the form of a dispersion as described in B) above, and the second component is in a solid form as described in A) above, the solid second component is immersed and mixed within the aqueous dispersion of the first component for a period of several hours before application to the water surface.
In each and every case the mixtures must either be well shaken to distribute the Bt-H14 toxin in suspension, just prior to application or a gelling aBent employed to avoid the need to agitate, as will be described later in this specification.
2) Duplex Film Formulation Compared with the monomolecular layer formulation this has an additional oil component as a major proportion of the content (90%-99%)-3) Foam Formulation This may be produced most easily from monomolecular layer formulation B) described above (but diluted with water to 1% a.i.) by the injection of air or other gases using foaming equipment as described in British Patent No. 1 561 088 or as mentioned on p.7.
The insecticide composition may include an extender such as water or an oil, for example a vegetable oil such as soya bean oil or coconut oil or a light mineral oil such as diesel oil, petrol oil, dieseline, etc.
The following table provides examples of the various formulations prepared as described above, giving the preferred concentration ranges for each ingredient.

- pc~ t) - ~26i~ 4 _ ... . . . .. , . .,.. , ~ .,, O V V I V
r~ O O O O O ~ ~, .
. ~ c~
x O O O O O O O O ~ O O O ~ O l x O~ !

zO I ~ ~ 00 00 0 000~ 000~

~1 x~ Q 2 o Q' ~ t~O

8 . _ ~ _ m - v - v - v~
s 8 o ~ e g. o ~ ~ 3 o .
.

e~ ee n. ~ x 8 ~ ~ 9 .~ 9 o ~ o . u7 ~ S r n ~268114 -page 7-The insecticide composition once formulated may be applied to the water catchment to form a monomolecular layer, as a self-spreading suspension or "slurry" by means of droppers, drip-feed reservoirs, spray equipment or by sorbent and inert materials which have been soaked in the concentrated mixture and which float on the surface of the water. The toxin component is thereby spread and maintained in an active state on or near the surface, giving excellent control of mosquito juveniles.
The foam forming material may be foamed in several ways. One method is to generate a gas (e.g. carbon dioxide) chemically within an aqueous suspension (1% a.i.) of a foam forming material. A second method is to bubble air or gas from a separate source, for example, a pump, a generator or a pressure cylinder (e.g. a commercial fire extinguisher) through an aqueous suspension of foam forming material.
A third method is to inject high pressure air or gas through fine holes into a branch pipe simultaneously with an aqueous suspension of the foam forming material, the relative volumes of air or gas and foam forming material being adjusted to provide the desired texture of the foam layer. In yet another method the insecticide composition is expressed under pressure through a special foam forming nozzle which entrains air into the composition thereby producing a stable water-insoluble foam.
It is preferable that the foam layer formed is at least O.lcm in thickness. The foam may be applied at a rate of 1.0 to 5.0 g of active ingredient per square metre which forms a foam layer about O.l to 0.5 cm in thickness and which may reduce to a single bubble layer eventually, which is, nevertheless, still effective.
When the surface of the water catchment is moving, the surface must be made static by employing a physical barrier, e.g. by means of a ~268114 -page 8-buoyant boom tethered or anchored around the appropriate area.
Suitable physical barriers are described in British Patent Specification No. 1 561 088.
Ideally an insecticide composition contains no unspecific toxin or pollutive materials, and the materials used are biodegradable.
The following examples illustrate the improved killing properties of insecticide compositions according to the invention compared with the toxin from B. thuringiensis var.H14 alone.
A) EXAMPLE OF ENHANCED FLOTATION OF TOXIN BY MONOLAYER
The comparison is made between (a) Bt-H14 preparation alone and (b) Bt-H14 + "Monoxci" monomolecular layer (Monoxci is a mixture in water of cetyl, stearyl and oleyl alcohol monoethoxylates in a ratio of about 25:25:50 or 15:35:50 as described in Patent No. 1 557 804) added to the same area of surface in identical separating funnels (A & B) with bottom outlets for withdrawing aliquots at various time intervals.
Procedure (i) Place 100 ml distilled water in each of A and B, (ii) Place 100/ul of preparation (a) on surface of water in A and 100 ~l of (b) on surface in B.
(iii) Draw off 8 ml of liquid from each of A and B at various time intervals tl, t2, t3, ... etc.
(iv) Place these aliquots on the surface of 200 ml of water in series of bowls A'tl, A't2, ... B'tl, B't2 ...etc., each containing 25 third instar larvae of Ae-aegypti .
(v) Determine larval mortality in each bowl after 24 hours.

12681~4 -page 9-ResuIts TABLE I

-Time Mortality (%) (t) hours (A) series (B) series _ Remainder: 60 100 Conclusions The presence of Monoxci monomolecular layer has a positive flotation effect on the dense Bt-H14 particles such that no significant amounts of the latter sediment from the surface during the first 18 hours. In the absence of monomolecular layer the Bt-H14 particles sediment rapidly at the outset (91% larval kill within 2 hours) thus when used in the field this material would be largely inaccessible to the feeding larvae.

268~
-page lO-B) EXAMPLES OF SURFACE SPREADING OF TOXIN BY MONOLAYERS
(1) The comparison is made between (a) Bt-H14 preparation alone and (b) Bt-H14 + Monoxci monomolecular layer added to the first section (A) of a 2 metre long trough which is divided into 4 x 50 cm sections (A, B, C, D) each containing 3 litres distilled water.
Procedure Place 0.6 ml aliquots of this mixture or sample to be investigated, on the surface at the extreme end of the trough, in Section A. After two minutes place dividers between sections to confine the larvae. Add 10 mosquito larvae to each section.
Record mortalities after 24 hours.
Results TABLE II

% Mortalities Section A B C D

Bt-H14 alone 100 O O O
Bt-H14 + Monoxci 100 100 100 100 Conclusions Bt-H14 toxin is carried by the spreading monomolecular layer over ? water catchment surfaces for a distance of at least 2 metres from the source of application and, judging from the period of time the monomolecular layer retains the Bt-H14, shown in experiment (A) above, the Bt-H14 may be carried for the full distance covered by - ~268~14 -page 11-the monomolecular layer. This is normally to the full extent of the available water surface, provided sufficient monomolecular layer is present to cover that surface completely.

(2) Using 100% (non-aqueous) monolayer and Bt-H14 mixtures, similar experiments to the above but including a final 'overflow~ test were carried out where 2 litres of water are passed through the end of the trough during a 12-hour period, draining the excess monolayer + Bt-H14 out of the system, into a container (E) where the overflow is bioassayed as in the other sections, when the process is completed.
These experiments were carried out to determine the difference in spreading effectiveness of the following monolayer compositions, under the same conditions and concentrations;
namely 10 ~1 of a 1% mixture of Bt-H14 in the monolayer concentrate.
(i) 90% oleyl alcohol monoethoxylate + 10% cetyl/stearyl diethoxylate, (ii) 90% oleic acid monoethoxylate + 10% cetyl/stearyl diethoxylate.
Results Representative examples are:
TABLE III
Monolayer (i) - alcohol ethoxylate (Ae. aegypti, 24 hrs.) Section A B C D E TarAL

.
Live larvae 0 0 0 2 6 8 Dead Larvae 10 10 lO 8 34 72 -" lZ6~ 4 -page 12-TABLE I_ Monolayer (ii) - acid ethoxylate (Ae. aegypti, 18 hrs.) Section A B C D E TOTAL

Live larvae O 0 4 8 5 17 Dead larvae 1010 6 2 35 63 C) SOLUBILITY TEST
The monolayer under test is applied to the surface of water in a vessel (A) which is sealed at the bottom by a dialysis membrane which permits only the passage of molecular species (with a molecular weight below about 20,000 Daltons). This vessel is then placed within a second vessel (B) containing water so that both water surfaces equilibrate to the same level. A surface balance probe, which measures the presence of adsorbed monolayers, is inserted into the surface of the water in (B). Measurements of the adsorbed monolayer surface pressure (clean water surface pressure = O dyne/cm) are made after various time intervals.
Results TABLE V

Surface pressure (dyne/cm) at:
Time (hrs) 1/4 1/2 1.0 2.-0 16.0 20.0 Monolayers described in this application O O O O O O

811~

-page 13-It is clear that the monolayers disclosed in this application are substantially insoluble in water. Similar results are obtained when the dialysis membrane is replaced by a 0.45 mm nylon mesh.

General Conclusions Both acid and alcohol ethoxylated monolayers impart very good spreading properties to the toxin particles resulting in a synergistic action on mosquito juvenile control and exhibit no water solubility characteristics.
Synergism of the mixture is due to two factors, viz:
l. The retention of the dense toxin crystal within the surplus monolayer material (the unspread reservoir) on the water surface so that it is prevented from sinking out of reach of the feeding juveniles, 2. The spreading of the toxin crystals by, and subsequent release from, the surface-active monolayer, such that the toxin is made available to the juveniles over a much wider area of the water catchment.
D) COLLOIDAL STABILISATION OF TOXIN COMPONENT
To prevent sedimentation of the toxin and maintain homogeneity of the mixture, agitation is normally required. In drip-feed or slow-release applications homogeneity is of particular importance. To improve the retention of the toxin by the bulk monolayer material (thus maintaining homogeneity) it is proposed to use a gelling agent or viscosity modifier. This has several important advantages:
a. It eliminates the necessity for vigorous shaking in the field prior to application, b. It allows more efficient spreading of the toxin in monolayer format as the latter hiodegrades over longer periods, by ~2G~3~i4 -page 14-retaining the toxin for longer periods within the 'reservoir' from which it would otherwise sink out of reach, c. Being continuously suspended within the hydrophobic monolayer material the toxin is protected from contact with water which is a prerequisite for enzymic degradation (proteolysis), an important failing of B.t. toxins, d. Similarly the u.v. absorption of the components of the monolayer mixture protect the toxin in suspension from u.v. degradation, another important failing of B.t. toxins.
The viscosity modifier or gelling agent is added in appropriate amounts to obtain the degree of stability required for the purpose in hand. By altering the content of such agents and/or their chemical nature it is possible to produce mixtures which release the toxin particles at various rates. Thus at one extreme a 'gel' can be made, containing about 4-5% w/w of the agent, which releases the toxin over long periods (several weeks) whereas when the content is lowered to about 0.01% w/w, a more rapidly releasing mixture is obtained which, nevertheless, is sufficiently stable to enable easy homogenisation prior to application.
The desirable compromise between the stability and economic factors is a mixture containing about 0.5~ w/w of the preferred agent, viz: Fumed silica ('Cabosil') (trademark)but other gelling agents (see hereunder) may have different optimal concentrations.

. ,,,, ~.

-page 15-Examples of Gelling Agents The following is a list of agents in the order preferred:
a. Fumed silica ('Cabosil') Used over the concentration range of 0.01% w/w to 10.0~ w/w in the monolayer concentrate material (i.e.
in the absence of water), with 0.1% to 10% w/w of Bt-H14 toxin as a dry or primary powder, depending on the bio-activity of the latter.
b. Aerosil 200 Used at up to 5% content.
c. Bentane SDl or SD2 Used at up to 5% content.
d. Aluminium stearate Used at up to 5% content.
e. Hartolan LD6080 Used at up to 5% content.

Examples of Monolayer Materials suited to Gelling The preferred monolayer composition for use with this gelling agent is a mixture containing 90% w/w oleic acid _ oleyl alcohol condensed with 1 mole of ethylene oxide and 10% cetyl/stearyl acids or alcohols condensed with 2 moles ethylene oxide (Monoxci-100) but the other monolayers quoted in U.K. Patent 1557804 are also suitable.
The mixture (MONTI)(trademark) used in obtaining the test results given below comprised:
Monoxci-100 (trademark): 95-99% w/w Bactimos (trademark) (Bt-H14) primary powder: 5- 1% w/w Cabosil (fumed silica): 0.1-1.0% w/w but where the content of the gelling agent is varied over the limits given, the other percentages are adjusted to suit.

~ ~6~ 4 -page 16-Test Procedure Samples of the monolayer concentrate containing the bacillus toxin at the concentration of approximately 60 ITU Ae/ae/mg (although this can be varied over a wide range) and with different concentrations of the gelling agent (in the preferred case, fumed silica or CABOSIL) are well shaken and small aliquots extracted immediately from the surface region of the samples and applied to the surface of the water containing 25 second instar larvae.
Similar aliquots are tested after the samples have stood for various periods. Mortality of larvae is assessed after 24 hrs.

Results In Table VI are shown the data obtained using BACTIMOS
(Biochem SA) primary powder @ 12,000 ITU Ae/ae/mg and in Table VII are data obtained with BACTIMOS and SKEETAL
(trademark) (Microbial Resources Ltd.) Bt-H14 samples. In addition are shown several results where the monolayer material employed is AROSURF (trademark) (Sherex Corporation).

, ~

-page 17-TABLE VI
Using MONTI
% mortality obtained with aliquot taken from extreme Cabosil %upper layer of samples left standing for (hrs):
w/w 0 4 6 24 (after v. slight agitation) .
0.1 100 73 27 100 0.3 100 87 67 100 0.4 100 67 33 100 0.5 100 88 53 100 1.0 80 67 47 87 0.0 (control) 100 0 0 0 I
Test organism: Second instar Aedes aegypti larvae.
N.B. The control sample also gave zero mortality when the aliquot was taken from the middle layers.
___ TABLE VII
MonolayerBt toxin % gel Mortality with aliquots taken after:
agent O hrs 2 hrs 6 hrs 24 hrs -Arosurf Skeetal 0.5 47 33 20 7 Monti Skeetal 0.5 100 93 73 67 ArosurfBactimos 0.5 80 20 20 13 Monti Bactimos 0.5 100 100 87 100 Arosurf Skeetal 0 27 20 13 13 Monti Bactimos 0 100 40 20 13 __ ._ __ _ _ _ ___ _ _ _ _ __ ~page 18-In Fig. l is shown the rate of sedimentation of the gelling agent boundary at a concentration of the agent where sedimenation i9 fast enough to measure and which appears to be a preferred concentration for practical use. Aliquots taken from the lower regions of the sedimenting samples, i.e. underneath the sedimenting boundary (made visible by the presence of the toxin component) always gave high mortalities close to 100%, whereas samples taken from the clear regions above this boundary always gave low mortalities. The toxin is therefore retained within the gel structure and does not sediment through it. Such partly sedimented suspensions are readily rendered homogeneous by upending the vessel several times. The boundary at 0.5% concentration, never sinks below the 47% volume level. Higher concentrations of gel agent retard the sedimentation and increase the minimum boundary level and at 4% concentration and above, a permanent stable suspension obtains which requires no mixing and shows no sedimentation boundary. These gel preparations give prolonged effectiveness and require less frequent application to the breeding site.
(E) STATIC TESTS
These tests of Monoxci-Bt-Hl4 mixtures without gelling agent against C. fati~ans larvae were carried out by Dr.S.H. Ho of Singapore University. (Monoxci: 15% a.i. aqueous dispersion) Monoxci and Bti were mixed in the ratio of 6:1 (w/w). Different dosages were tested against various juvenile stages.
l) Larvae 20 egg rafts were put into each fibre glass tank containing 60 litres of water (area of water surface = 6528 sq. cm). The larvae were allowed to hatch and grow to the appropriate stages for the experiments. The chemical mixtures were spread on the water surface. Six samples were taken from each tank after 48 ~6~14 -page 19-hours. For each sample the numbers of live and dead insects were recorded (Table VIII).
TABLE VIII
Effect of Monoxci-Bti mixtures on the mortality of larvae of C.
fati~ans .
Stageg. of Monoxci- No. of larvae (48 h) 48 h %
Bti mixtureAlive Dead mortality 2nd larvae 0 77 0.06 2 144 98.6 0.3 0 145 100 0.6 0 71 100 4th larvae 0 53 0 0 0.06 1 54 98.2 0.3 1 53 98.1 0.6 0 44 100 -2) Egg Hatch 3 replicates of 1 egg raft per plastic tank were set up. The number of larvae that hatched from each raft and mortality of the first instar larvae were recorded (Table IX).
NOTE: The results obtained from the 3 replicates of each treatment in all experiments were pooled.

-page 20-TABLE IX
Effect of Monoxci-Bti mixtures on the hatching of eggs.

-g. of Monoxci- No. of eggs that ~ of dead larvae Bti mixture hatched (1 day) (4 days) .

0.003 325 100 0.015 282 100 0.03 292 100 Conclusions The monolayer/Bti mixture is a very effective C. fati~ans larvicide .

Claims (14)

-page 21-The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An insecticide composition for controlling insects which have an aquatic breeding site comprising, a first component which is capable of forming either an insoluble monomolecular layer, an insoluble foam layer or duplex film layer on the surface of a water catchment and a second component which has a toxic action on larvae giving rise to a synergistic mixture..

2. A composition for controlling insects which have an aquatic breeding site comprising a first component capable of forming an insoluble monomolecular layer on the surface of a water catchment and a second component derived from Bacillus Thuringiensis or Bacillus Sphaericus having a toxic action on larvae, the first and second component together forming a synergistic mixture.

3. A composition for controlling insects which have an aquatic breeding site comprising a first component capable of forming an insoluble foam layer on the surface of a water catchment and a second component derived from Bacillus Thuringiensis or Bacillus Sphaericus having a toxic action on larvae, the first and second component together forming a synergistic mixture.

4. A composition for controlling insects which have an aquatic breeding site comprising a first component capable of forming a duplex film layer on the surface of a water catchment and a second component derived from Bacillus Thuringiensis or Bacillus Sphaericus having a toxic action on larvae, the first and second component together forming a synergistic mixture.

page 22

5. A composition as claimed in any one of claims 2, 3, or 4 wherein the first component comprises at least one compound of general formula:
CmH2m?1.(OR)n OH or CmH2m+1.(OR.OB)nOH
and/or at least one long chain compound of the general formula:
CmH2m?1.CO.(OR)nOH or CmH2m?1.CO.(OR.OB)nOH
where R and B are alkylenes and may be the same or different, n is an integer in the range of 1 to 3 and m is an integer greater than 14 but excepting isostearyl ethoxylates.

6. A composition as claimed in any one of claims 2, 3 or 4, wherein the first component comprises a mixture of cetyl, stearyl and oleyl alcohol or acid mono or diethoxylates.

7. A method of controlling the breeding of insects which have an aquatic phase in their life cycle comprising forming either a monomolecular layer, an insoluble foam layer or a duplex film layer on the surface of a water catchment and adding a second component having toxic action on larvae.

8. A method as claimed in claim 7 wherein the second component is Bacillus Thuringiensis toxin.

9. A method as claimed in claim 7 wherein the second component is a Bacillus Sphaericus toxin.

10. A composition as claimed in claim 2, 3, or 4 including a gelling agent or viscosity modifier.

11. A composition as claimed in claim 2, 3, or 4 including a gelling agent, said gelling agent comprising between 0.01% w/w to 10.0% w/w in the first component.

12. A compositon as claimed in claim 2, 3 or 4 including a gelling agent, said gelling agent comprising fumed silica between 0.01% w/w to 10.0% w/w in the first component.

-page 23-

13. An insecticide composition for controlling insects which have an aquatic breeding site comprising a first component which is capable of forming either an insoluble monomolecular layer, an insoluble foam layer or a duplex film layer on the surface of a water catchment, a second component which has a toxic action on larvae, and a third component comprising a gelling agent or viscosity modifier which inhibits sedimentation of the second component from the first component, the first and second components together forming a synergistic mixture.

14. A composition as claimed in claim 13, wherein the first component comprises at least one compound of general formula :
CmH2m ? 1.(OR)nOH or CmH2m?1.(OR.OB)nOH
and/or at least one long chain compound of the general formula :
CmH2m ? 1.CO.(OR)nOH or CmH2m ? 1.CO.(OR.OB)nOH
where R and B are alkylenes and may be the same or different, n is an integer in the range 1 to 3 and m is an integer greater than 14 but excepting isostearyl ethoxylates.