Abstract:
Small creatures from the group of insects and worms which are pathogenic to humans, animals and plants can be controlled effectively by applying or introducing an aqueous percarboxylic acid solution containing one or more percarboxylic acids with 1 to 6 carbon atoms to surfaces and/or into water. A solution which contains peracetic acid and/or performic acid is preferably used. In the case of insects, the larvae of these are controlled in water using an application concentration of 1 to 5000 ppm of percarboxylic acid.

Description:
FIELD OF THE INVENTION 
     The invention relates to a process for controlling and destroying pathogenic small creatures, in particular insects and worms. 
     BACKGROUND OF THE INVENTION 
     For as long as anyone can remember, humans and animals and also plants have been plagued or harmed by a variety of pathogenic small creatures from the groups of insects and worms. Mosquitoes, such as malaria-carrying anopheles mosquitoes, and the larvae of schistosoma (trematodes) which cause bilharziasis may be mentioned by way of example. 
     There has been no lack of effort to eradicate malaria. Thus, the insecticide DDT was previously sprayed in large amounts in order to control the mosquitoes. However, the good effects had to be balanced against damage to the ecological equilibrium and the use of DDT has now been banned. 
     The use of chlorine-releasing agents, such as sodium hypochlorite, has also been tried. Again, this agent did not gain general acceptance because it is difficult to handle and, when used in inland waters, it inevitably leads to undesirable salt production and the formation of undesirable chlorinated organic compounds. In tropical and sub-tropical countries, attempts have also been made to lower the surface tension of waters by using surfactants in order to prevent the larvae remaining below the surface of the water. The disadvantages of this technique, these being responsible for the limited use of this method, are that some of the mosquitoes can escape from the range of spread of the surfactants and/or too large an amount of surfactant is required. 
     U.S. Pat. No. 5,393,781 discloses controlling zebra mussels in cooling circuits by using a peracetic acid solution. This document does not mention any other classes of animals which could be controlled using peracetic acid. The use of peracetic acid as a microbicide for controlling bacteria, viruses, yeasts, algae and moulds has been known for a long time. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a process for controlling and destroying disease-causing and/or troublesome insects which does not have the disadvantages inherent in the methods used hitherto, or exhibits them to a much smaller extent. 
     The object is achieved by a process for controlling and destroying small creatures from the group of insects and worms which are pathogenic to humans, animals and plants, by the application or introduction of a liquid controlling agent to surfaces and/or in waters, which is characterised in that an aqueous percarboxylic acid solution, containing one or more percarboxylic acids with 1 to 6 carbon atoms, is used as the controlling agent. 
     The small creatures to be controlled, wherein “controlled” is understood to mean a reduction in the population, are small creatures from the classes of insects and worms which are pathogenic to humans and animals. The process according to the invention relates in a particular manner to the control of pathogenic insects by destroying the larvae in their preferred habitat. The preferred habitat of larvae is a moist medium, in particular substantially stagnant, shallow waters such as near the banks of lakes, ponds, paddy-fields, swamps and the like. Pathogenic worms can be controlled in the same way, wherein application in shallow waters is of special importance. Examples of insects which are present in tropical and sub-tropical areas and which can be controlled according to the invention are mosquitoes, flies and bugs which transfer unicellular organisms, threadworms and viruses by stinging or on contact and may thus cause serious illnesses. Examples are, when they sting, anopheles mosquitoes that introduce plasmodia which lead to malaria; sandflies that introduce leishmania which causes kala-azar skin disease; tse-tse flies that transfer trypanosoma which initiates sleeping sickness; certain mosquitoes that transfer viruses which cause dengue fever; other mosquitoes that transfer the agent which causes yellow fever; finally the midges which are present in particular in the vicinity of paddy-fields and which cause Japanese encephalitis, should be mentioned. 
     Among the pathogenic worms which need to be controlled, the schistosoma (trematodes, leeches) which cause bilharziasis are of particular importance. Infection takes place through contact of humans with freshwater and brackish water in which schistosoma larvae are present. To control the larvae, it is expedient to treat shallow, stagnant waters, in particular in the vicinity of the bank, with a solution of percarboxylic acid. Tapeworms and threadworms which are pathogenic to fish and which live in water can be controlled in a similar manner. 
     To control larvae of, for example, worms which live in the vicinity of the surface of soil, such as hookworms which can lead to ancylostomiasis following contact with the skin, percarboxylic acid solution can be applied to the soil at an effective concentration. 
     An effective concentration of percarboxylic acid(s) in the medium being treated is normally in the range from 1 to 5000 ppm, in particular in the range from 10 to 500 ppm. The treatment of surfaces, such as soil or water surfaces, can be achieved by means of spraying equipment which is conventionally used for agricultural purposes, such as large spray guns or vehicles with wide booms which are provided with nozzles. For the treatment of surface layers of water, percarboxylic acid solution may also be introduced directly into the water and distributed by means of appropriate mixing devices such as pumps or ship&#39;s propellers. 
     The percarboxylic acids to be used, which are also called peroxycarboxylic acids, may be monoperoxy-C 1 -C 6 -monocarboxylic acids, monoperoxy- or diperoxy-C 4 -C 6 -dicarboxylic acids or monoperoxyhydroxycarboxylic acids with 2 to 6 carbon atoms and 1 or 2 hydroxyl groups. Examples are performic acid, peracetic acid, perpropionic acid, mono- and diperoxysuccinic acid, mono- and diperoxyglutaric acid, peroxylactic acid, peroxyglycolic acid and peroxytartaric acid. Peracetic acid, performic acid and solutions containing peracetic acid and performic acid are preferred. 
     In general, as a result of the method of preparation, the solutions contain hydrogen peroxide and the carboxylic acid(s) from which the percarboxylic acid(s) is/are derived. In addition, the solutions generally contain a mineral acid catalyst which accelerates establishment of the equilibrium. The highest peracid concentration which can be achieved during reaction of hydrogen peroxide with a carboxylic acid in the aqueous phase with a given ratio by weight of the reaction partners, is the equilibrium concentration. Accordingly solutions in or close to the equilibrium state or dilute solutions which have been obtained therefrom by diluting with water before use are used. The undiluted solutions to be used expediently contain about 0.1 to about 5 moles, in particular 0.2 to 2 moles, of percarboxylic acid per liter. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with a preferred embodiment, a percarboxylic acid solution is used which contains, as a result of the method of preparation, orthophosphoric acid, pyrophosphoric acid and/or polyphosphoric acid of the formula H n+2 P n O 3n+1 , wherein n is an integer equal to or greater than 3, in particular 3 to 10. The concentration of these types of phosphoric acids is generally in the range from about 0.1 to about 3 wt. %, in particular about 0.5 to about 1 wt. %. These types of solutions preferably contain peracetic acid or performic acid or both carboxylic acids as the percarboxylic acid, wherein this combination has preferably been produced in situ prior to use, for example by mixing a peracetic acid solution and a source of formic acid, such as formic acid or a water-soluble formate, and allowing the mixture to stand for from a few minutes up to a few hours. 
     An advantage of this type of solution is regarded as the fact that the phosphoric acid component is more beneficial from an ecological point of view than the conventionally used sulfuric acid, when introducing the percarboxylic acid solution into the medium to be treated, such as in particular water. An advantage which is provided by any percarboxylic acid solutions which contain a combination of peracetic acid and performic acid is the increased effectiveness as compared with solutions which contain only peracetic acid as the percarboxylic acid. Solutions with the two named percarboxylic acids also demonstrate benefits as compared with any solutions which contain exclusively performic acid as the percarboxylic acid because the manufacture of performic acid, for reasons of safety and handling, is not without its problems. 
     In accordance with another embodiment, the percarboxylic acid solution to be used also contains one or more surfactants. Readily biodegradable surfactants are preferred, such are those already used for controlling insects. These are in particular anionic and nonionic surfactants such as, for example, sugar surfactants, alkanol sulfates or ethoxylated alcohols. The surfactant concentration in the percarboxylic acid solution to be sprayed out or to be introduced directly into waters is selected in such a way that an effect is produced which is greater than the effect of the percarboxylic acid(s); an effect of this type is obtained with a concentration in the range from about 0.1 wt. % to about 10 wt. %. 
     Use according to the invention of solutions containing one or more percarboxylic acids and the process for applying the same differs from the known use of such solutions for controlling microorganisms and zebra mussels with regard to the objective, namely the control of pathogenic insects and worms. The new use permits pathogenic insects and worms to be controlled in an effective and technically simple manner by killing the larvae. The agent to be used, after the percarboxylic acid has been effective, is rapidly biodegraded so that no ecological problems are to be feared. However, care should be taken when choosing the concentration of percarboxylic acid(s) and hydrogen peroxide in a solution which is to be sprayed onto plants since high concentrations may also be toxic to plants. 
     The invention is explained by means of the following examples. 
    
    
     EXAMPLE 1 
     Controlling black mosquito larvae: water, in which 10 larvae were present, was inoculated with 50 ppm of peracetic acid (PAA) by using an equilibrium peracetic acid solution with a concentration of 5 wt. % of PAA and 27 wt. % of hydrogen peroxide. Within 12 hours after inoculation, 5 larvae died; the remaining animals exhibited symptoms which correlated with painful reactions in the gill tubules (doubling up and restless swimming to and fro). 
     EXAMPLE 2 
     Water containing 10 black mosquito larvae was inoculated with 50 ppm of peracetic acid using an equilibrium peracetic acid solution with a concentration of 5 wt. % of PAA and 27 wt. % of hydrogen peroxide and also 3 wt. % of Hostapur S30 (30% strength aqueous solution of a mixture of various secondary alkane sulfonates from Hoechst AG). Within 12 hours after inoculation, 6 larvae died. Here again the larvae which did not die demonstrated the symptoms of damage exhibited in example 1. 
     COMPARATIVE EXAMPLE 1 
     Water containing the same population of black mosquito larvae as in examples 1 and 2 was inoculated with 1500 ppm of H 2 O 2  using a 50 wt. % strength hydrogen peroxide solution. None of the larvae died. 
     EXAMPLE 3 
     Controlling mayfly larvae: water containing 10 larvae was inoculated with 7 ppm of peracetic acid using an equilibrium peracetic acid with a concentration of 5 wt. % of PAA and 27 wt. % of hydrogen peroxide. All the larvae were dead after 8 hours. 
     EXAMPLE 4 
     Controlling red mud worms (tubifecetes): Water, in which the experimental animals were present, was inoculated with 30 ppm of peracetic acid using an equilibrium peracetic acid solution with a concentration of 2 wt. % of PAA and 48 wt. % of hydrogen peroxide. All the animals died. 
     COMPARATIVE EXAMPLE 2 
     In the same way as in Example 4, water containing red mud worms was inoculated with 800 ppm of a 50 wt. % hydrogen peroxide solution. None of the experimental animals died. 
     EXAMPLE 5 
     A population of red mosquito larvae (chironimides) was inoculated by inoculating with 400 ppm of a 5 wt. % strength equilibrium peracetic acid solution (5 wt. % PAA, 27% H 2 O 2 ). All the larvae died within 2 hours.