CARRIER MATERIALS FOR MOSQUITO-LARVAE KILLING PESTICIDES, MOSQUITO-LARVAE KILLING PRODUCTS AND METHOD OF MANUFACTURING

THE SAME

The subjects of the present invention are carrier materials for mosquito-larvae killing pesticides (carrier composites), and mosquito-larvae killing products containing these carrier composites and one or more known larvicides (larvicide composites) and procedures of their manufacture.

Numerous insecticide preparations have already been developed for exterminating the adult mosquitoes. Several patent specifications, such as, for example, RU2077203; GB1097790; US4855319, DE2126684; EP498720; CN1297680; CH647392; JP57128615 disclosed preparations of this kind. However the resistency and extermination of other useful insects are problematic and there are non-avoidable side-effects.

Since the mosquito-larvae mainly live at water surface their extermination can be limited to the living area of mosquito larva (it is ca. 20 % of the living area of adult mosquitoes). Having realized this fact, a lot of larvicide have been developed and disclosed - for example in the patent specifications of US1831476; US5273967; US 4707359; GB546934 - that used mineral and vegetable oil derivatives to float on the water surface. A common disadvantage of these materials is the environmental damage.

Taking into consideration the environmental damage, some selective biological larvicides have also been developed. For example the followin patent specification provide teaching in this respect: US5830722; US5830722; US4206281 , CN1050667, FR2639959; WO00/62620; EP417906; US4316959; WO98/28984; DE4133889; WO98/39974; EP349769; US4918006; WO92/8354; SU1515425, SU1305916; RU2111667; RI2031579.

Most of these contain the protein toxins of Bacillus Thϋringiensis lsraelensis (Bti) and Bacillus sphaericus. These selectively exterminated the larva of the bloodsucking mosquitoes only, because these could destroy only the inner wall of the special digestion system of the larva of blood sucking insects.

Since the mosquito larva live on water surface, some floating carriers have also been developed to carry these biological larvicides, as it has been described in the following patent specifications: US4650792, GB650132, US 4228614, US4631857,

WO98/28984. The main disadvantages of these carriers are their inability to decompose in the environment due to their artificial polymer content. Some carriers are built up from natural constituents, e.g. from cork, but their structures are heterogeneous and are mechanically not strong enough. The other carriers decompose into different parts after contact with the water and the release of the larvicide from each particulate is not homogeneous. Another kind of carrier is the ice- containing carrier family, but working with ice-containing carriers in a hot climate is very problematic.

The mechanical strength of the low-density carriers is generally low due to the presence of large amount of air pores. Therefore, their spray from air-crafts is not useful due to their low level of stability towards mechanical impacts.

The best known solution for carrying the biological larvicides is given in a Russian patent specification RU 2,113,121 in which the fermentation liquor containing the B. sphaericus toxin is jellyfied with carboxymethylcellulose and the jelly is absorbed on perlite. This composite, however, does not contain any hydraulic or other binder, therefore it cannot be granulated and has not appropriate mechanical strength for spraying from air-crafts. Perlite has open pores, therefore it does not float on water surface even for a short time.

Presently no suitable carrier is available for biological or chemical larvicides which would ensure all of the required abilities such as floating/controlled time floating on water surface, controlled release of larvicide, environmental friendly with selective components, controlled sinking and decomposition time, good storage stability and mechanical strength for homogeneous spraying from air-crafts.

Therefore, we have developed some new carrier materials for mosquito-larvae killing pesticides (carrier composites) and mosquito-larvae killing products (larvicide composites) which fulfill all of the above mentioned requirements and have also developed some appropriate procedures for their manufacture.

During our early experiments a surprising effect of the jellyfied polysaccharides was observed which acted as structure modifying agents in hardening of some hydraulic binders. Modified starch, flour or cellulose derivatives can affect not only on hardening of hydraulic binders but on the properties of the formed composites. Some of these newly developed properties are preferred to reach our demands related to good quality carrier composites of mosquito larvicides.

The subjects of the present invention are the carrier composites, which have lower density than the density of water, containing one or more hydrulic binder, preferebly gypsum or cement or their mixtures, containing one or more foamed aluminosilicate, preferably pumicite or perlite or their mixtures, containing one or more modified polysaccharide, preferably modified starch, modified cereal flour, carboxymethyl cellulose, or (C1-2)alkyl-hydroxy-(C1-2)alkyl-ceIlulose derivatives, and containing both open and closed air-pores, furthermore the larvicide composites which consist of the abovementioned carrier composite and one or more known biological and/or chemical mosquito larvicide.

The relative ratio of the components in the carrier composite depends on the required final parameters of the carrier and the larvicide composite. Generally, the carrier composites consist of 0.5-99 %, preferably 20-80 % amount of foamed aluminosilicates, most preferably pumicite or perlite, 0.01-80 %, preferably 0.5-50 % amount of some modified polysaccharide, most preferably 20-40% amount of modified corn starch or wheat flour, 0.1-20% amount of a carboxymethylcellulose derivative, or 0.1-1.5% amount of an alkyl-hydroxyalkylcellulose derivative and one or more hydraulic binder, preferably gypsum or cement. The composites have 0.2-0.8 and 0.3-1.0 bulk densities or real densities respectively. Their mechanical strength is excellent.

The open pores of the carrier composite grains absorb the liquid containing the active larvicide and the closed pore systems, which cannot be filled with water or liquids, ensure the low density of the grains. The partial filling of open pores with liquids containing the larvicide (Fig.1), which solidify during the drying process of the larvicide composite, provide a barrier for water to fill these pores completely. When the liquid containing larvicide dissolves out after contact with water during the larvae extermination, the slow dissolution and release of the larvicide containing ,,plug" opens a way before filling up the pores completely with water. At this point, the extermination has already been finished (the larvicide completely dissolved out and killed the larva), and the water-filled pores cause increase in density of the grains. When this density becomes more than the density of the water, the grains sink. The time of dissolution of larvicide from the open pores and filling with water (this process cause of controlled sinking of the grains) is between 24-48 h. It is acceptable time to exterminate mosquito larva.

The use of the multilayer (preferably periodically changing active/inactive layers, with an inactive or active outer most layer) carrier granules and larvicide granules of the present invention, the larva extermination can be retailed or periodical. Since the carrier composites can stabilize the larvicide in the larvicide composites, use of carrier composites and larvicide composites of the present invention provide a possibility to exterminate mosquito larva by using the larvicide composites even spreaded in a previous larva extermination period. The dried and re-wetted composites can act again in a second larva-extermination period.

In the present invention, we have also developed a kind of larvicide composite containing a feeding attractant for mosquito larva. The attractant, preferably wheat flour, may be one of the components of the composite or can be carried on surface/in pores of the composite.

Optionally, the killer composite may contain a further attractant for the female mosquitoes to lay eggs on it. In this case, the female mosquitoes will lay eggs on the sites where extermination have been performed and will be performed again in the next season.

Other subjects of the present invention are the methods to prepare the above mentioned carrier and larvicide composite materials.

The preparation methods of carrier composites mainly consist of modifying (jellyfying) the polysaccharides (in case of previously modified cellulose derivatives it means dissolution and homogenization in water), addition of gypsum/cement and foamed pumicite/perlite in the appropriate amount to the modified polysaccharide solution, homogenising the mixture and programmed heat-treatment.

In case of starch or flour derivatives, the cold aqueous suspension of polysaccharide is poured into hot water to jellyfy them. Another possibility is to perform this jellyfication is to treat the polysaccharides with an alkaline solution/suspension. These alkaline solutions/suspensions may contain alkali- or alkaline-earth metal-oxide, hydroxide or hydrogencarbonate or alkali-carbonate solutions/suspensions. Most preferably alkaline solutions/suspensions are aqueous calcium oxide or calcium hydroxide suspensions. Temperature may be varied between 20 and 100 ⁰ C, the preferred temperature is the ambient temperature.

The calcium oxide promoted jellyfication can be performed with calcium hydroxide obtained from CaO and water before mixing it with the polysaccharide

powder and water, or with reaction of a powder mixture consist of CaO and the polysaccharides. The reaction temperature may be varied between 20 and 100 ⁰ C, most preferably the temperature is controlled by the reaction heat of CaO and water.

During our experiments a surprising effect of temperature on the properties of the formed carrier composite granules was observed. The most important properties, e.g. the floating ability, hardness, and the ratio of closed/opened pores strongly depends on the heat-treatment time and temperature.

When we used cement as hydraulic binder, the drying at the room-temperature gave appropriate results. In case of gypsum as hydaulic binder, when the structure modifying agents were cellulose derivatives, a two-step drying, one at 80 ⁰ C for 1 h and then at 180 ⁰ C for another hour gave satisfactory results. At higher temperatures or in case of a longer heat-treatment, the bound water is eliminated, the crystal structure is broken and the mechanical strength and floating ability is lost. Using gypsum as hydraulic binder and starch derivatives as structure modifying agents, a simple drying at 80-120 ⁰ C gave satisfactory results due to the formation of an inorganic-organic hybrid xerogel structure with appropriate ratio of closed/opened pores.

An especially preferred form of the present invention is a carrier composite which consists of a nucleus and more than one layers; the larvicide components are held by at least one of the layers (outer or inner).

The density of the inner solid nucleus is lower than the density of the water which makes the carrier composite to float at least for 48-72 h. It is built up from a material which is mechanically strong and environmentally acceptable. A preferred component of this type of nucleus is an ignited foamed clay, e.g. Liapor granulate or any of the above mentioned carrier composites whose density is lower than that of water. The properties needed to carry the active larvicide components relate to the outer layer materials (e.g. porosity, larvicide releasing ability, etc.). If the inner nucleus diameter is 2 mm, and the outer layer applied onto this nucleus is also 2 mm thick, then the volume of the outer layer will be 87.5 % of the volume of all the grains, therefore the properties of the composite will be expressed as 87.5 % of the properties of the outer layer. The carrier composite granulates may be multilayered and each layer property may be the same or different.

A preferable form of the present invention is a special kind of the multilayer carrier/larvicide composite granulates, the grains have an inner solid nucleus and may be built up from one or more outer layers which have larger density than the densitiy of water. The outer layers slowly dissolve/peel off when it comes in contact with the water. These outer layers consist of one or more hydraulic binder and/or the above mentioned carrier composites having density larger than that of the water. Since the average density of the grains, made up of the inner layer of the lighter density and outer layers of higher density materials, is more than the density of water the larvicide composites sink after spreading. The thickness, type and amount of the outer layers control the dissolution/peeling off time. After dissolution/peeling of some of the outer layers, the density of the inner nucleus becomes dominant and the granulates start floating. The release of the larvicides start and the extermination of the mosquito larva begins.

It gives a chance to perform the spreading of larva killing granules before vegetation. The granules are sunk in the water after spreading (before vegetation grows). Later (after large growth of vegetation when direct spreading is not possible) the outer layer of the granules are peeled off and these are lifted to the surface, the larvicide composites release the larvicide.

A preferred use of the larvicide compositions of the present invention is to spread a mixture of floatable and non-floatable larvicide composite granules together. One kind of the larvicide composite granules are sunk and will be lifted to release the active larvicide later (see above) and the other part floats immediately and exterminates the larva.

An other possible form of larvicide composition of the present invention is a granule which has an outer heavy layer containing an active ingredient. This kind of the granule can be used to exterminate live larva at the bottom of the ponds because the sunken granules release the active larvacide in the sunken state. Once the outer layer is peeled off the granule becomes lighter than the water and floats to the surface. The inner part now starts to release the larvicide at the surface of the water.

The other subjects of the present inventions are the methods to prepare the mosquito-larvae killing granules (larvicide composites). This involves combining of one or more biological or chemical mosquito-larvae killing agent as active constituent with the above mentioned carriers. The active ingredient could be one or more known

biological larvicides or a mixture of one or more known chemical or biological larvicides such as B. Thueringiensis or B. Sphaericus protein toxins.

One of the possibilities to prepare the larvicide composite granules is to cover the surface of the carrier composite with a glueing material containing the active ingredient or to cover the carrier composite with a pure glueing material and then treating the covered surface with the powder of the active ingredients.

Another possibility is to prepare granules of the larvicide composite with solutions or dispersions of the active ingredients that are absorbed on the surface or in the pores of the carrier composite granules. In this way different kind of materials can be used as solvent/glueing agents such as water, polyols or polysaccharides or their mixtures, preferably ethylene glycol, polyethylene glycols, glycerol, sorbitan, carboxymethylcellulose, and starch or alkyl-hydroxethyl cellulose derivatives can be used.

The absorption of the solutions/dispersions may be performed via immersion, solid/liquid mixing or spraying techniques.

Since our carrier can conserve the efficacy of the larvicides such as Bti carried on surface/in pores of the composites, the larvicide containing dried products can be stored for a long period of time. It is a further advantage of this invention. The Bti containing preparation that was used for 24/48 h in larva extermination was dried and later (after 2, 4, or 6 days) it was contacted with water (modeling of consecutive overflows), its efficiency in killing larva was over 80 % at 5-15 g/ha dose.

Our preparations have excellent mosquito-extermination ability, long-term activity, good mechanical strength, light weight, good spreadability from air-craft as well controlled floating and sinking time, together with excellent degradation without formation of any harmful material.

Without limiting the invention we present several examples of the carrier and larvcide composites and their preparation methods in the following.

Example 1.

20 kg of commercial starch (HUNGRANA Rt, Szabadegyhaza, Hungary) was suspended in 20 liter cold water, next 240 liter hot water was poured into this suspension when a jelly was immediately formed. A mixture of 10 kg of perlite (ALDO Ltd., Tokόl, Hungary) and 20 kg of gypsum (Rudagipsz Ltd, Rudabanya, Hungary)

were added to the jellyfied mixture during intensive stirring, when the mixture was transformed into granules with a special mechanical tool (the granule's height is 4 mm, diameter is 3 mm). The granules were dried at 80 ⁰ C, when the hardness was good and the bulk density was 0.25 kg/dm3. The 20 % of the granules was sink after 12 h, 80 % within 24 h and all of them within 36 h.

Example 2.

The procedure of example 1 was repeated but 15 kg of portland cement and the same amount of pumicite (Mardetti Bt., Erdόbenye) was used instead of gypsum and perlite. The drying was performed at room temperature, the bulk density was 0.29 kg/dm3.

Example 3

12 kg of commercial CMC (carboxymethyl cellulose with 36 % water-soluble sodium-salt content, Zoltek Co., Nyergesύjfalu) was dissolved in 50 liter of water which was stirred till CMC was dissolved. The solution was kept for 20 min, then 10 kg of perlite powder (P1 quality, ALDO Ltd., Tδkόl) and 100 kg of gypsum (Rudagipsz Ltd., Rudabanya) were added together with water to ensure the plasticity. After 5 min mixing the mortar-like mixture was granulated, the granules were dried at 80 ⁰ C for 1 h then at 180 ⁰ C for an other hour.

Example 4

An aqueous solution of 0.7 kg of sodium-salt free carboxymethylcellulose (MAVIBOND CP-O 8000) was added to a mixture of 10 kg of perlite and 20 kg of gypsum. After granulating the mixture, the granules were dried at 80 ⁰ C, the bulk density of the product formed was 0.25 g/cm3 With increasing the amount of gypsum up to 25 or 30 kg without changing the other parameters, densities of the formed granules were changed to 0.30 and 0.35 g/cm3 respectively.

Example 5

In analogy with example 4, but using 10 kg of pumicite instead of perlite and 30 kg of gypsum, the product obtained had bulk density of 0.30 g/cm3. Using 20 kg of

cement and 10 kg of gypsum instead of 30 kg of gypsum, the bulk density was increased up to 0.35 g/cm3.

Example 6

In analogy with example 5, 0.7 % hydroxyethylcellulose (Bermocoll E411 , Pointner and Rotschaedl, Baden b. Wien) in a mixture of 30 kg of gypsum and 10 kg of pumicite was used, the bulk density of the obtained product was 0.4 kg/liter.

Example 7

10 g of wheat flour was mixed with 0.5 g of CaO. The mixture was suspended in 32 ml of water, stirred for 3 h and a mixture of 3 g pumicite and 27 g of gypsum was added. Following the above mentioned granulating and drying method, the granules obtained had a bulk density 0.65 g/ml and 48 h floating time.

Example 8

A mixture of 5.5. g wheat flour and 1.4 g of corn starch were added to an aqueous suspension of 0.2 g of calcium hydroxide in 25 ml of water. The mixture was stirred at room temperature for 1 h. 9 g of a mixture of pumicite:gypsum (4:6 in weight) was added. After granulating and drying the granules obtained had a bulk density of 0.43 g/ml and a floating time of 24 h respectively.

Example 9.

Each of the the above mentioned granule was activated with a Bti (Bacillus Thϋringiensis Israelensis) (Vectobac WP, 5000 ITU ) powder suspended in an 1 % CMC (carboxymethylcellulose) solution. The amount of Bti was 4 % in the dried end- product. The drying was performed at 50 ⁰ C. The bulk densities were between 0.25 and 0.70 g/ml, diameter and height of the granules were 3 and 4 mm, respectively. The floating time varied between 12 - 48 h.

Example 10.

The efficiency of the larvae-killing was tested on Culex Pipiens larva in 24/48 cycles, with using the carrier prepared following the example 1 and example 9. The doses were varied between 5-15 kg/ha, when appropriate or complete efficiencies

were observed. After two days the granules were collected, kept dry for 2 days and used again to study the efficiency (in order to modelling the drying after the overflown and a new overflown situation). Similar experiments were done after keeping the granules in dry state for 4 or 6 days. The results can be seen in Table 1. The killing efficiency was counted in per cent with comparing to the untreated control samples.

Table 1

Efficiency at 5-15 kg/ha dose (% mortality) Dosage, kg/ha 5 10 15

Time, day 1 80 92 96

2 72 92 100

After two days storage in dry state

1 96 96 98

2 96 100 96 After 4 days storage in dry state

1 90 88 94

2 88 88 96 After six days storage in dry state

1 88 82 82

2 88 80 84

Taking into consideration the abovementioned results, a slow-releasing mosquito-larvae killing composite material has been developed, which has the required environmental, physical, chemical, biological and mechanical properties.