NO820962L - PREPARATION FOR ANTI-SNAIL CONTAINER, CONTAINER FOR THE ADMISSION OF THIS PREPARATION AND APPLICATION OF SUBSTANCES IN SNAIL POLLUTANTS - Google Patents

Abstract

The preparation to control slugs comprises at least one attracting substance for the slugs, at least one substance producing giddiness, invalidity or death, at least one feeding substance and water, and optionally a thickening substance. The substances are preferably selected among those found in the natural environment, with optionally slight modifications of their chemical composition and which are acceptable in food products.

Description

Snails of various species annually cause major damage to useful and ornamental plants. Numerous means have therefore been tried to combat snails [see, for example, the standard work by D. Godan "Schadschnecken und ihre Bekåmpfung", Verlag Eugen Ulmer, Stuttgart (1979)] - The best-known means for this are metaldehyde-based snail granules. Snail grains are in various respects unsatisfactory; they contain molluscicides,

which are highly toxic to birds, mammals and also to humans; they are preferentially consumed by granivores; Creped snails can be eaten by other animals, for example hedgehogs, which are thereby also poisoned. In humid weather, snail pellets are less effective or even have no effect. The poisoned snails still drag themselves over long distances and leave unappetizing slime trails. The crepitated snails often have to be collected and destroyed.

The home remedy beer is relatively expensive, attracts only over a short distance, dissolves quickly, it has to be buried in the ground in cups, which, with the wrinkled snails and the dissolved beer, have to be removed and destroyed.

The invention is based on the task of providing a means for combating snails, which does not exhibit the above-mentioned disadvantages of the known means. In particular, the agent should be non-toxic to humans and other animals. Furthermore, the agent must be easily and immediately usable and not leave any residues of alien species in or on the soil.

The preparation according to the invention for combating snails

is characterized by the fact that it contains

(a) at least one snail bait; (b) at least one precursor; (c) at least one substance that has an anesthetic and/or coordination-disrupting and/or paralyzing and/or killing effect on snails;

(d) water, and

(e) optionally a thickener,

which components preferably consist of substances that occur in nature, or are easily chemically modified and/or permitted in food products.

A further object of the invention is an anhydrous concentrate of the above-mentioned preparation, which concentrate is diluted with water before use.

The subject of the invention is also the use of an ester

of a lower to medium carboxylic acid, especially with up to 10 carbon atoms, preferably up to 5 carbon atoms, with a lower to medium monohydric alcohol, especially with up to 10, preferably up to 5 carbon atoms, or a mixture of . such esters as bait for snails.

The object of the invention is furthermore a method for the protection of plant cultures against snails, characterized in that an effective amount of a preparation according to the invention is added to the culture soil at intervals.

The ingredients in the preparation according to the invention preferably consist of substances that occur in nature as such, or are slightly chemically modified, i.e. methylated, ethylated, propylated, methoxylated, ethoxylated, propoxylated, carboxymethylated, acetylated, propionylated or hydrated, and/or are permitted for living means, i.e. harmless to humans.

Among other things, beer can be used as an attractant, but better results have been obtained with esters of lower to medium carboxylic acids with monovalent lower to medium alcohols, i.e. snails were lured from an environment with a larger radius, and in the presence of alternative attractants they were said esters preferred. Preferably an acetate, preferably ethyl or a propyl acetate, a butyrate, preferably n-butyrate or isobutyrate, especially their methyl, ethyl or a propyl ester, is used. Mixtures of the aforementioned esters, in particular of a butyrate, two different acetates and a formate, give particularly good results. These lower aliphatic esters of up to 7 carbon atoms are generally used in concentrations of up to 2 parts by weight, calculated for the entire preparation. The higher aliphatic and aromatic esters can only be used in relatively low concentrations, as they act as a deterrent, increasing with increasing molecular weight.

The advantages of these baits which can be used according to

the invention, is:

- greater effectiveness, lure radius of 2 to 3 m (versus max

10 cm at the current bran baits).; - lower price compared to natural and synthetic flavors;

- chemical resistance, primarily against oxidation,

unlike conventional aromas;

- effect on all snails; all were found in the traps

in Central Europe, naked snails and the house snails that appear as damage snails.

Monovalent lower alcohols, e.g. ethanol, isopropanol, isobutanol, isoamyl alcohol and others.

Ethanol is preferred because of its low toxicity to other living beings, its additional luring effect and low enrichment tendency in the snails. Preferred concentrations are approx. 3 to 25% by weight, especially 5-15% by weight, calculated on the entire preparation. At concentrations of the order of 10% by weight, the narcotic and paralyzing effect occurs very quickly after the first contact. The higher alcohols are, in accordance with their LD^Q value, effective in lower concentrations, but are increasingly rejected by snails with increasing amounts of the alkyl residue. Too high an alcohol concentration also repels the snails.

The alcohols preferably used as component (c) in the preparation according to the invention, for example lower alcohols, especially ethanol, are distinguished, as natural products or substances that can be produced from plants, by their environmental friendliness; they are easily volatile and biodegradable, so that unused amounts evaporate or break down and nothing is left in the soil.

Ethanol, the propanols and isobutanol not only serve to anesthetize and paralyze the snails, but exert an additional luring effect. They also serve simultaneously to preserve the preparation and as dissolution mediators for the less polar components.

Instead of an alcohol, which first anesthetizes the snails, then paralyzes and only later kills, for component (c) a direct molluscicidal substance can also be used alone or possibly together with an alcohol. Such molluscicides are edible and/or contact toxic and cause irreversible damage. Suitable for this are, for example, known molluscicidal substances for terrestrial snails, such as metaldehyde and carbamates, but also molluscicidal substances that have so far only been used for aquatic and amphibious snails with bilharziosis control. To this last group belong especially substances found in each from endod (Phytolacca dodecandra), further in Phytolacca americana, Balanites aegyptica,

Sapindus saponaria, Swartzia madagascariensis, Polygonium senegalense and the like.

Such molluscicides probably act mainly

upon contact; the presence of precursors in the preparations used serves to cause the snails to stay longer, thereby extending the contact time.

Such molluscicidal substances are also suitable for use in

a paste or gel-like preparation, which is distributed in small quantities on the soil between the plants. In this way, the provision of depressions in the soil is made redundant, however, the dead snails lie unappetizingly around the garden and are not protected from being eaten by snail-eating beneficial animals, as with the trap application of the alcohol-based mixture, by which the dead snails are submerged in a highly deterrent-made opaque liquid, which is shaken with soil such that it is filled with dead snails.

The above-mentioned molluscicides of plant origin are not toxic to cultivated plants. They can be incorporated into the preparation in the form of dried powdered leaves, however preferably in aqueous and especially in alcoholic (for example ethanol, isobutanol) slurry. As they are mostly also toxic to other living beings in the soil, for example soil, it is recommended that they are either used in a preparation containing a thickener or, if the preparation does not contain any thickener, in a hydrophobic vessel.

When the preparation according to the invention is to be used directly

in soil depressions or in porous vessels, the addition of a thickener to the preparation is recommended. As a thickener, substances known to the person skilled in the art can be used, for example carbohydrates of a natural nature, such as alginates, carrageenates and galactomannans, or of a biosynthetic nature, such as xanthan gum or scleroglucans, semi-synthetic thickeners, such as derivatives of cellulose, starch, alginates and galactomannans -mannans, crystalline thickeners of a mineral nature, such as bentonites and highly dispersed silicic acid or of an organic nature, such as microcrystalline cellulose, synthetic thickeners, such as polyacrylates or polyvinyl alcohols.

The thickener should satisfy different requirements. Thus, for example, it should be alcohol-resistant and biodegradable, and its viscosity should not be affected by temperature during use and hardly change during long-term storage. In order for the thickened mixture when used as a trap not to seep too quickly into the soil, the thickening component should also be resistant to the digestive enzymes (cellulase, amylase, galactomannanases) released from the killed snails, whereby it has been shown that all natural and semi-synthetic hydrocolloids are rapidly attacked, associated with strong viscosity reduction, with one surprising exception, xanthan gum, which is absolutely stable. The higher and the more regularly esterified or etherified semi-synthetic hydrocolloids are, the more resistant they are to enzymatic hydrolysis. -Therefore, a commercially available special hydroxyethyl cellulose, which is sold by Hercules under the name "Natrosol-B" thanks to regular etherification, is more enzyme resistant than the other cellulose derivatives, although it is advantageous to add one of the known cellulose inhibitors. Also a highly etherified hydroxypropyl guar is relatively stable against enzymatic attack by snail enzymes.

The preparations according to the invention can be flowable, but also paste or gel-like. Flowable preparations are preferably pseudoplastic or thixotropic with a rapid regeneration ability; it is important that the thickened mixture exhibits such a flow property that, on the one hand, it does not seep into the soil or penetrate the porous substrate, and on the other hand, that the snails sink into it when used as a trap. The thickener should therefore, as far as possible, not reduce the interfacial tension, so that soil wetting is kept as low as possible, should exhibit the highest possible water retention, so that water diffusion to the surrounding soil is reduced as much as possible,

and should exhibit a high resting viscosity with pseudo-plastic flow behaviour, so that the mixture is prevented from being pushed away into the soil.

Since it is the only natural hydrocolloid that meets all the above requirements, a heteropolysaccharide with a molecular weight of several million is preferred as a thickening agent, which can be produced by fermentation of carbohydrates with bacteria of the species Xanthomonas. Each basic unit of this heteropolysaccharide is composed of monosaccharides (glucose and mannose). and glucoronic acid. This heteropolysaccharide is available as a commercial product, for example 'Rhodopol 23' from Rhone-Paulenc, 'Kelzan' from Kelco, 'Xanthan Gum' from Ceca. For the sake of simplicity, the polysaccharide defined above shall be referred to in the following as xanthan gum, as is generally customary in the technical literature, although other products of the same or similar composition may also be used.

Solutions with xanthan gum behave pseudo-plastic, i.e. they liquefy under the influence of shear forces, but regain their original viscosity after setting the impact.

Preparations according to the invention which contain xanthan gum as a thickening agent, due to their pseudo-plasticity, can be easily poured out of a container, for example a bottle, and then in a resting state regain their high resting viscosity, whereby, when directly placed in an uncoated recess in the ground, a seepage into the ground is avoided. For this reason, concentrations of 0.4 to 1.2% by weight of xanthan gum, calculated for the preparation, are already sufficient. In this way, the preparation according to the invention can be added to depressions in the soil without the use of additional vessels. After the snails crept through the effect of the preparation according to the invention are found in this recess, it can simply be covered with soil. This eliminates both the mucus traces from poisoned animals and the unappetizing collection and destruction of the still alive poisoned or crippled animals. Both the preparation and snails then serve to fertilize the soil by rotting.

Although the preparation according to the invention is preferably and most easily exposed in depressions in the soil, as the walls of the depression are advantageously made dimensionally stable by gentle pressure if the soil is loose, it can also be used in containers of various kinds.

Such a container should have an opening of such a nature that with the aid of the attractant they are attracted and, for example, by the alcohol vapors and absorption of the alcohol-containing preparation, anesthetized snails can fall into the container. Because of the falling and viscously moving slugs, shear forces are developed which reduce the viscosity of a pseudo-plastic preparation. The initially high resting viscosity is then restored. Consequently, the snails cannot free themselves from a thickened, highly viscous preparation, as the alcohol also rapidly paralyzes the muscles. Eventually the snails perish as the alcohol penetrates through the skin and mouth. The administrators can

after application is easily eliminated by covering with soil.

To avoid the unappetizing detour of removing the container, one can, as further described above, add the preparation directly into the soil depressions or use a container or a surface formation that can rot or dissolve. Such a container can be pressed into the ground or placed in a recess in the ground. With the surface formation, the recess can be coated. After the snails have entered, the container or flat formation in the recess is covered with soil. The remaining residues are non-toxic, biodegradable and also serve to fertilize the soil.

Suitable materials for making such containers

or surface formations that can rot or dissolve are fibrous materials, such as peat, wood shavings, semi-chemical cellulose pulp and chemical pulp or water-swellable or dissolvable foils of the indicated thickener. The vessels can be a few centimeters deep and, for example, 10 cm in diameter. Fibrous surface formations can also be treated with known hydrophobic or impregnating agents on the side that comes into contact with the solution, so that this cannot penetrate, but so that moisture can penetrate from the other, untreated side, whereby rotting can occur. It is recommended to fill such containers or soil depressions covered with such surface formations to the edge of the preparation.

With the preparation according to the invention, a snail trap can be provided by pouring the thickened solution into a soil depression. In this way, the small soil slope also plays a role as a mechanical obstacle, as the foot muscle-paralyzed snails cannot get over this and fall back into the solution. Component (c), for example alcohol, acts together with the thickener component as "snail glue". The alcohol as a snail nutrient is primarily non-toxic, but after 5-10 minutes of heat contact it paralyzes the snails' foot muscles, so that they cannot free themselves from the preparation. Only secondarily should the snails sink due to alcohol absorption through the skin.

The agent causes the snails to absorb and thus to come into contact with the preparation, so that the alcohol or the molluscicidal substance diffuses into the snail's body and can, in the case of the alcohol, paralyze the foot muscles. Mono-, di- and oligosaccharides (preferably sucrose, fructose and glucose, for example in the form of starch syrup, invert sugar or molasses), dextrins and native or pre-glued starches, microcrystalline cellulose, vegetable or animal proteins (such as casein, powder of skimmed milk, the wheat and corn glutinous substances obtained during starch production), crushed or very finely cut plants or fruits, possibly in processed form as a concentrate or extract, preserved or spray-dried are i.a. suitable intermediaries. These mediators or, more advantageously, mixtures of these mediators are used in quantities, limited by price,

of 1-5% by weight, calculated on the entire mixture.

The preparation according to the invention may, in addition to the components

(a) to (d) and. A thickener also contains additional substances such as evaporation retarders, stabilizers and denaturants.

Known evaporation-retarding agents are used to avoid premature drying of the preparation by evaporation of the liquid components, and to regulate the release of bait quantities. When using the preparation, they generally form a monomolecular covering layer over the liquid surface, whereby evaporation can be reduced by 50-80%. Preferred evaporation-retarding agents are the natural cetyl alcohol, which should also occur in plant wax, or ^ i^- 22~^'et alcohol with 1-3 ethoxide residues, in an amount of 0.5-1 per mille by weight, suitably incorporated in such a way that the evaporation-retarding agent possibly under heating in advance dissolves into component

(c) in the preparation according to the invention.

All actual food-permitted preservatives reduce the preparation's true effect, as the substances in question scare away the snails, only hexamethylenetetramine in concentrations between 0.1 and 1 per million by weight is tolerated to some extent. It is therefore appropriate to dispense with an actual preservative, and protect the preparation according to the invention against microbial attack by means of the alcohol and pH. As has been shown by inoculation experiments, at 12% by weight ethanol and a pH of 5.5, no seed growth takes place.

As a deterrent for warm-blooded animals, the pure active substance in Cayenne pepper or paprika, or in other Capsicum species, Capsaizin, or the "synthetic Capsaizin", pelargonic acid vanillamide, is preferably used in concentrations of 0.01 to 0.05 per thousand by weight; the unisolated Capsaicin in the form of ground Cayenne pepper or as Chillies aroma concentrate can also be used. It is also possible that the active substance in black pepper, piperine and its isomers, is also used unisolated as ground pepper or as a crude extract. The pelargonic acid-vanillyl-amide is given preference, because it is commendable at its very low usage concentrations, as it does not trigger any deterrent reaction in the snails at the effective concentration, as it is oxidation-stable and as its burning taste effect occurs without delay immediately upon absorption.

The preparation's pH range is generally 4-8.5, preferably in the acidic range, especially at 5-5.5, adjustable for example by adding small amounts of non-toxic, biodegradable, preferably organic acids or salts; in particular, dicarboxylic acids, hydroxydicarboxylic acids and hydroxycarboxylic acids are suitable. The water content of the usable mixture can be up to 90% by weight.

The preparation according to the invention exhibits various advantages over the known agents for combating snails.

It can be made up of completely natural ingredients, so that no harmful foreign substances are left in the garden. The mixture can be used in all kinds of weather, as the snails in dry weather prefer the moist mixture to an even stronger degree, and as the rainwater in rainy weather runs off the thickened mixture into the surrounding soil. Thanks to the aforementioned attractants, the agent is also effective for pure green leaf eaters (this includes many house snails), in contrast to the known bran- and protein-containing grains.

If ethanol is used as a paralyzing component, it results

a completely harmless mixture, as the killed snails lie hygienically in the soil depressions, submerged in the non-transparent, highly deterrent solution so that they are avoided by snail-eating beneficial animals, except that these beneficial animals can metabolize ethanol, so that no harmful substances accumulate residues in them if these animals after all absorb ethanol.

If a vegetable molluscicide, active substance, such as that from endod is used, the result, compared to conventional molluscicides, is a harmless mixture, however, endod exhibits a lowest lethal dose of 3.2 g/kg for mice and induces severe nausea in many warm-blooded animals animals. Thanks to the strong attractant, such a mixture can be used more purposefully and sparingly than the known grains, which are more or less randomly found by the snails.

In principle, a distinction must be made between two forms of use for the preparation according to the invention, namely use (a) in the trap principle with alcohols as paralyzing component; (b) on surfaces with genuine molluscicidal active substances. Examples 1-4 are examples for (a) and example 5 is an example for (b).

Example 1

A preparation is made from the following components:

The sucrose is dissolved in water, the other components are added to the alcohol, after which the alcoholic mixture is added to the aqueous mixture with good stirring, with further stirring for approx. 1/4 hour until complete swelling of the xanthene gum.

The thickened solution was poured directly into a soil depression which was excavated with a hand shovel. Such soil depressions were constructed at distances of approx. 2 to 4 m, and each was filled with approx. 0.5 to 1 dl of the thickened solution. It was determined that the effect is greater the deeper the liquid level is, the steeper the surrounding soil slopes are and the thinner the solution.

The snails were attracted and began to eat at the tip of the thickened solution. Only after a certain time, as a result of the ethanol absorption through the mouth and feet, did they try to crawl out onto the thickened solution, whereby they sank down with their foreparts and could not turn around. Then, paralyzed by the dermal absorption of alcohol, they lost their hold and sank. It was also observed how the snails, after eating the thickened solution, probably as a result of partial paralysis, spread out during the crawling away and thereby dipped into the solution, from which they could not free themselves and where they finally perished after absorption of a lethal amount of ethanol through the skin.

The effect of the agent took place very quickly, already after a few evening hours when the liquid-filled recesses are full of dead snails. The effect of the solution lasted, depending on the weather, the nature of the soil and the number of dead snails, for approx. 2-3 nights. After this time, the depressions were covered with soil, as long as they had not already collapsed by themselves. In part, the solution was added again when the contents with the dead snails had settled.

Example 2

According to the literature, beer is an excellent snail attractant (see Godan, loe. eit.), and beer was therefore chosen as a reference.

(a) In a two-chamber system with which the snails in one chamber were offered beer, and in the other chamber a bait used according to the invention, the following distribution resulted as 20 snails of the species Arion rufus were brought to the starting position in each of the three independent attempt:

(b). In an experiment in a greenhouse with soil traps at 4 m distances with a preparation, as in example 3A, and an attractant mixture with the composition 40% ethyl isobutyrate, 20% ethyl

acetate, 15% isopropyl acetate, 5% propyl acetate, 5% methyl isobutyrate, 5% methylbutyrate, 5% ethyl propionate, rounded off with other esters up to 7 carbon atoms, the following results were obtained: The mixture was on average ten times more effective than beer, since at two snail species were caught over 90% and in another species 75% of. the exposed snails.

The best capture results were given by the lower esters with up

to 6 carbon atoms in concentrations of a total of 1-1.5 parts by weight, whereby esters with a branched chain appeared to be more attractive than the straight chain ones. Serious deterrent reactions seem to occur with these esters only from 2 parts per million by weight, and this turning point seems to be species-specific. The higher esters, however, triggered deterrence reactions already at early lower concentrations, which was associated with a clear reduction in effectiveness, so that they were only used in concentrations of a total of 0.1 parts per million by weight to round off the bait mixture.

The 2 parts per thousand of lower esters specified in the example are softened by the cetyl alcohol, which also retains the esters by approx. 50%.

Example 3

The precursors have an extremely correct function, as they bring the snails to contact the mixture for a long time, so that the paralyzing or killing component can have its effect. As the following examples show, the effect of the mixture can be increased quite significantly with the suitable raw materials, whereby it should not be ruled out that the natural raw materials themselves emit volatile substances in very small quantities which enhance the effect of the esters.

The base composition is that of example 1, the bait mixture is that of example 2 (b), the precursor and pH are supplemented and vary as follows:

Mixture:

A = as example 1 with 2% sucrose, but additionally 0.05%

hexamethylenetetramine, pH approx. 7.5;

B = as example 1 with 2% sucrose, but additionally 2%

starch syrup (consisting of glucose, maltose and oligosaccharides), adjusted to pH 5.5 with citric acid;

C = as mixture B, but also with 1% wheat bran and 1%

skimmed milk powder;

D = as mixture B, but also with 1% flour from malt and 1%

skimmed milk powder;

E = as mixture B, but also with 1% finely powdered

casein;

F = 2% sucrose and 1% homogenized spinach, pH 5.5;

G = as mixture B, but with 1% wheat bran starch;

H = as mixture B, but with 1% native maize starch.

Citric acid was used for acidification. With these different preparations, the following field trials were carried out:

Time: End of May

Place: Grass slope with bushes along a street Experimental arrangement: Alternating Al, Bl, Fl.., A2, B2, F2.. etc,

for every 3-4 m, 0.7 dl of thickened solution was poured into standardized recesses - paraffinized cardboard cups - in such a way that, for example, there was a 1-2 cm high wall above the solution as a mechanical obstacle. The diameter of the front recesses: 6 cm.

Species spectrum: The species spectrum captured seemed, as far as could be determined by observation, to agree with the frequency of occurrence of the individual species.

Mainly present were: Arion rufus, predominantly animals below 5 cm, above that, Arion subfuscus, few animals of Arion silvaticus, Deroceras, some other nudibranchs, of the house snails from Helicigona arbustorum sporadically frequent, some Cepaea, in phases undetermined small house snails frequent. In the following, the total number of snails of the nudibranchs acting as pests and larger house snails is given, the small house snails caught in larger numbers in phases are not listed.

Under A to F and A, G, H, it concerns two different experiments, where A served as a reference.

Cups with more than 40 snails were, depending on the size of the snails, to be termed as full, i.e. the dead snails were tightly packed in them, so that no further snails could find a place in them.

Example 4

Example 3 was repeated, but instead of xanthan gum the following thickener was used: (a) 1.3% by weight "Natrosol" 250 H4BR from Hercules (a high-molecular, particularly regularly substituted hydroxyethyl cellulose) and 0.1% by weight "Aubigum X2" from. Ceca (a cold water soluble carrageenate), pH 5.5 with citric acid. (b) 1.2% by weight "Jaguar" HP60 from Stein-Hall (a highly substituted hydroxypropyl guar) and 0.1% by weight "Kelgin HV" (an alginate).

2% lactose is preferably added as a cellulase inhibitor. - The alginate and carrageenate additions should act as aids against leaching, as they gel the surrounding soil with the potassium ions (carrageenate) or with the calcium ions (alginate). In addition, these algae additives also mix a dissolved protective layer around the snails, which prevents the exit of the digestive enzymes. The results were comparable to the results from example 3. However, preference is given to the xanthan gum because of its greater safety of use and because of its naturalness. Cold water-soluble carrageenate, which would be suitable for use alone, is too expensive for this.

Example 5

Endod is added to the previous mixture in addition to the ethanol. Thereby, the mixture does not need to be used in the trap principle, but can be applied directly to the soil in small quantities, possibly in small natural troughs, at distances of 2 to 3 m. The snails are irreversibly damaged by the endod upon contact with food and leave to the ground next to the strained mixture.

The mixture is prepared exactly as in example 1, with the same composition or with one of the compositions in example 2, except that 0.1-10% by weight, preferably 1-5% by weight, of endod berries are also finely chopped in the ethanol, and that the in the aqueous part for stabilization of the active endode substance, 0.5% by weight of citric acid/citrate buffer is dissolved for a pH value of 5.5 together with 0.3% by weight of ascorbic acid. It is recommended to raise the concentrations of two components from Example 1, to compensate for the faster volatilization in the surface application, the attractant to 0.3% by weight and, to prevent the mixture from flowing onto the soil, the xanthah gum to 1, 2% by weight. All percentages refer to the entire mixture.

Next to the small quantities of the described preparation poured directly onto the ground were dead snails.

Claims (22)

1. Preparation for combating snails, characterized in that it contains (a) at least one snail bait; (b) at least one nutrient; (c) at least one substance that has an anesthetic and/or coordination-disrupting and/or paralyzing and/or killing effect on snails; (d) water, and (e) optionally at least one thickener. 2. Preparation according to claim 1, characterized in that the components (a) to (e) consist of substances that occur in nature or are slightly chemically modified, and/or are permitted for foodstuffs. 3. Preparation according to claim 1, characterized in that it contains as an attractant an ester of a lower to medium carboxylic acid and a lower monohydric alcohol or a mixture of such esters. 4. Preparation according to claim 3, characterized in that it contains as an attractant at least one ester with up to 8 carbon atoms, consisting of an aliphatic carboxylic acid with a monovalent aliphatic alcohol, preferably in a concentration of 1 to 2 parts per thousand by weight, calculated for the entire preparation. 5. Preparation according to claim 4, characterized in that it contains as an attractant an acetate, n-butyrate or isobutyrate, preferably the methyl, ethyl or propyl ester thereof, or that it contains a mixture of these esters based on a butyrate and at least two acetates. 6. Preparation according to one of claims 1-5, characterized in that it contains as component (c) at least one lower monohydric alcohol, preferably ethanol. 7. Preparation according to one of the claims 1-5, characterized in that it contains as component (c) one or more active molluscicidal substances, preferably one or more active natural substances with the same or similar structure as the substances that have been investigated for combating water-dwelling snails and found in the plants Phytolacca dodecandra, Phytolacca americana, Balanites aegyptica, Sapindus saponaria, Swartzia madagascarensis, Jatropha sp., Theo leosa, Croton tiglium, Schima argenta or Polygonum senegalense and related species, or one or more known synthetic active substances. 8. Preparation according to one of claims 1-7, characterized in that it contains a thickening agent which consists of at least one preferably natural or modified natural hydrocolloid and is pseudoplastic. 9. Preparation according to one of claims 1-7, characterized in that it contains a water-swelling thickener and is viscous to pasty or gel-like. 10. Preparation according to one of claims 2-9, characterized in that it contains as a thickening agent a heteropolysaccharide which is produced by fermentation of carbohydrates with bacteria of the species Xanthomonas. 11. Preparation according to one of claims 2-9, characterized in that it contains high-molecular enzyme-resistant hydroxyethyl cellulose as thickener. 12. Preparation according to one of claims 1-11, characterized in that it contains at least one agent from the group of carbohydrates, preferably sucrose, fructose, glucose and their dimers, oligomers and polymers, animal and vegetable proteins and their hydrolysates, preferably skimmed milk or casein powder , ground, crushed or cut up, fresh or processed plants, preferably bran or malt flour. 13. Preparation according to one of claims 1-12, characterized in that it contains, as additional aids, an evaporation-retarding substance, preferably cetyl alcohol, and a deterrent for warm-blooded animals, preferably Capsaicin or pelargonium vanillylamide. 14. Preparation according to one of claims 1-13, characterized in that it is in the form of an anhydrous concentrate which must be diluted before use. 15. Use of an ester of a lower to medium carboxylic acid and a lower to medium monohydric alcohol or a mixture of such esters as an attractant for snails. 16. Use according to claim 15 of an ester with up to 8 carbon atoms of an aliphatic carboxylic acid and a monovalent, aliphatic alcohol or mixtures thereof, preferably an acetate, n- or isobutyrate, preferably in the form of a methyl, ethyl or a propyl ester, or preferably mixtures containing at least one butyrate and two acetates. 17. Use according to claim 15 or 16, in a liquid or pasty preparation for combating snails or in a concentrate of such a preparation. 18. Method for the protection of plant cultures against snails, characterized in that the cultivated soil is supplied at intervals with an effective amount of a preparation according to one of claims 1-13. 19. Method according to claim 18, characterized in that the cultivated soil at the edge of the plantings is provided with depressions at intervals and the preferably liquid or pseudoplastic-pourable preparation is filled into these depressions, and the depressions are covered with soil as needed after the snails have crept therein. 20. Method according to claim 19, characterized in that the soil depressions are provided with a container or surface formation for the absorption of a liquid preparation, which rots or dissolves in the soil under the influence of moisture. 21. Method according to claim 20, characterized in that the container or surface formation is hydrophobic on the surface that comes into contact with the preparation. 22. Method according to claim 18, characterized in that a paste or gel-like preparation is applied in an effective amount to the soil between the plants.