WO2008037966A2

WO2008037966A2 - Pest control

Info

Publication number: WO2008037966A2
Application number: PCT/GB2007/003615
Authority: WO
Inventors: Andrew David Key
Original assignee: Andrew David Key
Priority date: 2006-09-26
Filing date: 2007-09-24
Publication date: 2008-04-03
Also published as: WO2008037966A3; GB0618965D0

Abstract

A rodenticidal composition comprising an edible substrate and an alcohol, wherein the composition comprises the alcohol in an amount which is toxic to a rodent.

Description

PEST CONTROL

The present invention relates to the field of pest control, and in particular to the control of household pests such as rodents such as mice and rats. More particularly, the invention relates to methods, uses and compositions suitable for controlling such pests, for instance using rodenticidal compositions capable of killing rats and/or mice.

A number of alternative strategies for the control of pests such as rodents are known. For instance, mechanical traps are commonly used to kill rats or mice, or to trap them for relocation or humane disposal. In certain situations, biological control may be effected by predators such as cats. However, these methods often suffer from disadvantages in terms of convenience, efficacy and safety.

Rodenticides are toxic substances that are used to kill rodents. Rodenticides are often used as the pest control method of choice due to their efficacy in rapidly controlling large populations of rodents. However rats and certain other vermin may be difficult to kill with poisons because their feeding habits reflect their scavenging lifestyle. They often eat a small amount of a potential foodstuff and then wait a certain amount of time. If they suffer no adverse effects, they will continue to eat the food. On the other hand, the term "bait shyness" is used to refer to the situation where a rodent eats a sub-lethal amount of bait, feels sick and associates the sickness with the bait. The rodent then refuses to eat the bait again. An effective rat poison is therefore preferably tasteless and odorless in lethal concentrations, or may have a delayed effect such that the rodent no longer associates the sickness with eating the bait several days earlier.

Another major problem with rodenticides is their toxicity. Incidences of poisoning of humans and household pets by rat poison are still not uncommon. A number of highly toxic substances have been widely used in managing rodents, including arsenic, strychnine and cyanide. Although some newer rodenticides exhibit lower toxicities in humans compared to rodents, many are still considered to be a major health hazard. Some commonly used rodenticides are discussed below. Metal phosphides have been used as a means of killing rodents. A mixture of food and a phosphide is left where the rodents can eat it. The acid in the digestive system of the rodent reacts with the phosphide to generate the toxic phosphine gas. This method of vermin control has possible use in places where rodents immune to many of the common poisons have appeared.

Zinc phosphide is typically added to rodent baits in amount of around 0.75-2%. The baits have strong, pungent garlic-like odor characteristic of phosphine liberated by hydrolysis. The odor attracts rodents, but has a repulsive effect on other animals. The tablets or pellets may also contain other chemicals which evolve ammonia which helps to reduce the potential for spontaneous ignition or explosion of the phosphine gas.

Phosphides do not accumulate in the tissues of poisoned animals, therefore the risk of secondary poisoning is low. Phosphides are the slowest acting rat poisons with exception of the coagulants, resulting in the rats dying in open areas instead of in the affected buildings. Phosphides used as rodenticides include aluminium phosphide, calcium phosphide and zinc phosphide.

Cholecalciferol (vitamin D3) is used as a rat poison, which is toxic to rodents for the same reason that it is beneficial to humans: it helps in calcium absorption in the body. In rodents it causes hypercalcemia, raising the calcium level sufficiently that blood vessels, kidneys, the stomach wall and lungs are mineralised (form crystals), leading to heart problems and bleeding and possibly kidney failure. In family pets, accidental ingestion is generally considered safe for cats but dangerous for dogs.

The botanical preparation of red squill, containing a cardiac glycoside as an active ingredient, was used as a rodenticide for many years. In theory, rodents ingest the product, and because they are incapable of vomiting, develop glycoside intoxication and pulmonary edema. Because humans are capable of vomiting, red squill was considered harmless, even to children. This product is not used much today because of its limited effectiveness as a rodenticide. Alphanaphthyl thiourea (ANTU) is another rodenticide that is said to produce pulmonary edema in rodents but not in higher mammals.

Strychnine is a plant alkaloid that, in the past, was used widely as a rodenticide. This agent is not used much today but is reported to have caused 3 deaths in 1998. Thallium is another older rodenticide commonly used in third world countries, where it commonly leads to intoxications. Arsenic was widely used as a rodenticide until 2 decades ago. It may still be found in liquid form in old barns and storage sites. Other rodenticides may be based on barium or yellow phosphorus.

The most commonly used rodenticides today are the anticoagulants, for instance the coumarins based on warfarin. Fatal internal bleeding is caused by an overdose of anticoagulants such as brodifacoum, coumatetralyl or warfarin.

Anticoagulant rodenticides inhibit the enzymes responsible for recycling of vitamin K, which ultimately reduces production of certain blood clotting factors involved in the thrombin clotting cascade. There is no effect on circulating clotting factors, so a lag time between poisoning and bleeding problems is seen. The lack of coagulation factors causes the animal to bleed to death because the blood does not clot. First-generation coumarins may be deadly with a larger single dose or smaller doses over multiple days. Clinical signs are usually seen 3-5 days after exposure. Second-generation coumarins and indandiones are toxic with a single dose. Second-generation coumarins are a greater hazard than first-generation coumarins if a dog or cat eats a poisoned rat or mouse. Treatment, once symptoms appear is more difficult, expensive, and has a much poorer prognosis than treatment that starts immediately after ingestion.

In the United States in 2003 nearly 20,000 human exposures to rodenticides were reported. Anticoagulant rodenticides were associated with 16,822 of these rodenticide exposures. Additionally, 14,916 exposures, the vast majority, occurred in children younger than 6 years. The long-acting, superwarfarin anticoagulants produced such symptoms in 144 of 16,481 cases. 4 deaths were reported from these rodenticide exposures. Two of these deaths occurred from a long-acting, superwarfarin rodenticide exposures, and 1 from strychnine. In Brazil, children younger than 5 years incurred 31 % of all rodenticide exposures and 23 exposures resulted in death; 20 of these were intentional suicides.

Many of the patients presenting with rodenticide ingestions are children who ingest such substances by accident and, thus, usually ingest small quantities. The literature relating to such ingestions is prone to the bias that an ingestion may not have actually occurred or it occurred at such a low dose as to be inconsequential. Thus, determining the treatment of a child based on published literature is potentially dangerous. Adults who ingest such substances are most likely attempting suicide; however, poisoning homicides may occur with these agents because of their ready availability.

Another problem with the use of poisons to control pests is that many populations of rodents have developed some degree of resistance, particularly in the case of warfarin-based anticoagulants. Although some newer rodenticides may be designed to overcome this problem, they are often expensive and only accessible to a limited group of users.

Consequently there is a need for further compositions suitable for controlling rodents, which are effective, safe and which can be made from readily-available and inexpensive ingredients.

According, the present invention provides a rodenticidal composition comprising an edible substrate and an alcohol, wherein the composition comprises the alcohol in an amount which is toxic to a rodent.

In a further aspect, the present invention provides a rodent bait comprising a rodenticidal composition as defined above.

In a further aspect, the present invention provides a method for killing rodents, comprising laying a rodent bait as defined above, for consumption by the rodents. In a further aspect, the present invention provides use of an alcohol for killing rodents, for example for controlling rodent populations.

In a further aspect, the present invention provides use of a rodenticidal composition as defined above as a rodenticide or rodent bait.

The present invention advantageously provides a safe and effective method for controlling rodent populations, using inexpensive materials. Although alcohol is toxic in humans as well as rodents, it is much less toxic than many commonly used rodenticides and therefore presents a much lower risk to human health. Since its effects are highly dose-dependent, rodenticide preparations can be provided in package sizes which are toxic or lethal to rodents but which are well below the toxic threshold for household pets and children.

The rodenticidal composition of the present invention comprises an edible substrate. The function of the edible substrate is to facilitate ingestion of the alcohol by the target rodent. Thus the edible substrate may be formed from any material which can be consumed by a rodent.

Preferably the edible substrate comprises a (preferably solid) rodent foodstuff. Suitable rodent foodstuffs include paper, cardboard or wax. More preferably the rodent foodstuff comprises flour, such as corn flour. Alternatively the edible substrate may comprise a liquid rodent foodstuff. In one preferred embodiment, the edible substrate comprises (either alone or in combination with a rodent foodstuff as mentioned above) a sweetener (such as saccharin) or sugar (for instance in the form of molasses or a refined sugar). The use of a sweetener or sugar enhances the taste and palatability of the composition to rodents. For instance, the composition may comprise icing sugar, preferably in an amount of 1 to 30 %, for example 5 to 20 %, based on the total weight of the composition. The edible substrate preferably comprises 10 to 90% of the total weight of the composition, more preferably 40 to 70 % by weight. The rodenticidal composition also comprises an alcohol, which is the active ingredient of the composition responsible for toxicity in rodents. The alcohol preferably comprises ethanol or methanol, or a mixture of ethanol and methanol in any proportion.

The composition comprises the alcohol in an amount which is toxic to a rodent. The toxic amount may vary according to the nature of the rodent to be targeted, for example mouse or rat, and the specific alcohol used. A skilled person may determine a suitable amount of the alcohol required for toxicity using well-known toxicological methods. For instance, trials may be performed using compositions containing varying amounts of alcohol. The effect of each composition when administered to the rodent is then observed. Rodents to be tested may be allowed to freely consume the composition, and the toxic amount of alcohol may be determined based on a mean amount of the composition consumed by each animal. Alternatively, a fixed amount of the composition (for instance a typical amount consumed by a rodent in a single feed) may be force-fed to each test rodent.

Toxicity may be assessed by measuring pathological symptoms and markers in tested animals. For instance well-known histological, biochemical and behavioural signs of alcohol toxicity (such as necrosis of liver tissue, the induction of liver enzymes, loss of motor function and/or consciousness) may be detected by analysis of tissue or blood samples or observation of tested animals.

A composition comprising toxic amounts of the alcohol may be sufficient to control a rodent population. This is because ingestion of a toxic dose by a rodent may lead to adverse effects such as reduced ability to feed, increased vulnerability to predators and disease, and compromised reproductive potential, even if the composition does not directly cause immediate death. However, the composition preferably comprises the alcohol in an amount which is lethal to a rodent. The lethal dose may be determined in the same way as toxicity discussed above, with death of the rodent being the observed criterion. A lethal dose may be considered to be a dose which kills half the members of the tested population, which is sometimes expressed as the LD₅₀ value (typically a constant mass of the test substance per unit body mass of the test animal). The oral LD₅₀ of ethanol in rats is known, and values for other rodents are available in the literature to a skilled person. In rats the oral LD₅₀ is 8.83g/kg on average, 10.6g/kg in young rats and 7.06g/kg in aged rats. Thus for a typical 250 g rat, the lethal dose is typically around 4 g ethanol. Considering that a rat might typically consume around 10g of material in a single feed, the composition of the present invention preferably comprises around 40% alcohol, more generally 10 to 90%, 30 to 60% or 35 to 50% alcohol by weight, based on the total weight of the composition. Although the lethal dose of alcohol will be lower for smaller rodents such as mice (e.g. a typical 3Og mouse might be killed by less than 0.5 g ethanol), compositions containing a percentage of alcohol within the above ranges may also be suitable for controlling smaller rodents, since the amount of bait consumed is typically proportional to body mass.

The rodenticidal composition of the present invention may be prepared by mixing together the edible substrate and the alcohol. The composition may comprise one or more further ingredients as necessary.

The composition may be packaged into any suitable container for laying as a bait. Preferably the rodenticidal composition is enclosed in a sealed package or sachet, in order to prevent loss of the alcohol by evaporation. For instance, the composition may be packaged into stick-shaped sachets formed from a thin, clear plastic sheet material. The plastic is preferably thin enough such that rodents can detect the presence of a food material in the sachet, and easily bite through the plastic to reach the composition contained within. In some embodiments the packaging may be coated with an external rodent attractant such as synthetic chocolate. The synthetic attractant can be a synthetic smell, preferably a sweet smell, and may be in the form of ink which is impregnated onto the outside of the sachet. In a particularly preferred embodiment the synthetic attractant is synthetic chocolate smell. Each sachet preferably contains 5 to 50 g (e.g. about 10 g or about 20 g) of the composition.

In a particularly preferred aspect of the invention the composition is in the form of a gel. A gel form is advantageous because it reduces the evaporation of the alcohol. Thus the gel form of the composition can be used by itself or in conjunction with a sachet as described above.

Alternatively, liquid preparations according to the present invention may be administered using any suitable apparatus such as a drip feeder, bottle or similar devices.

Rodent populations may be controlled by laying the bait (such as the plastic sachets mentioned above) in any location where infestations occur. The bait may be laid indoors or outdoors as required. Consumption of the bait may be monitored and further bait laid as necessary.

The invention will now be described by way of example only with reference to the following non-limiting, specific embodiments.

A rodenticidal composition was prepared by mixing 3.5 litres ethanol, 4.0 kg corn flour and 0.7 kg icing sugar. The composition was packaged into (cylindrically- shaped) stick sachets each 105 mm in length and 18mm in diameter. Each stick sachet is coated with synthetic chocolate as a rodent attractant and printed with safety and other user information. The stick sachets are layed as bait in an area showing signs of infestation with rats. The bait is monitored daily for signs of consumption by rodents and population numbers are estimated by observing droppings or counting sightings of live or dead rats. After 2 weeks the rat population may show a significant decrease in numbers, for example a 25 to 100% reduction in rat numbers.

In a further example, the above method was repeated using 3.5 litres methanol instead of ethanol in the rodenticidal composition. In a still further example a rodenticial composition according to the present invention is prepared in gel form by adding 2Og of methocel SGA50M powder to 150 ml of boiling water and dispersing it completely. To this is added 730 ml of ethanol. Care is taken to ensure that the mixture is completely lump free. One hundred and fifty grams of glucose and 20ml of toffee extract are then added to the mixture.

The mixture is refrigerated for at least 2 hours to thicken fully. The composition is used by itself or is packaged into sachets.

Claims

1. A rodenticidal composition comprising an edible substrate and an alcohol, wherein the composition comprises the alcohol in an amount which is toxic to a rodent.

2. A rodenticidal composition according to claim 1, wherein the alcohol comprises ethanol or methanol.

3. A rodenticidal composition according to claim 1 or claim 2, wherein the edible substrate comprises flour, paper, cardboard or wax.

4. A rodenticidal composition according to any preceding claim, wherein the rodent is a rat or a mouse.

5. A rodenticidal composition according to any preceding claim, further comprising a rodent attractant.

6. A rodenticidal composition according to claim 5, wherein the rodent attractant comprises chocolate.

7. A rodenticidal composition according to claim 5, wherein the rodent attractant is a synthetic composition having a chocolate smell.

8. A rodenticidal composition according to any preceding claim, wherein the edible substrate further comprises sugar.

9. A rodenticidal composition according to any preceding claim, comprising the alcohol in an amount of 10 to 90 % based on the total weight of the composition.

10. A rodenticidal composition according to any preceding claim, wherein the composition comprises the alcohol in an amount which is lethal to a 250 g rat following consumption of 10 g of the composition by the rat.

11. A rodenticidal composition according to any preceding claim, comprising at least 400 g alcohol per kg of the composition.

12. A rodenticidal composition according to any preceding claim wherein the composition is in the form of a gel.

13. A rodent bait comprising a rodenticidal composition as defined in any preceding claim.

14. A method for killing rodents, comprising laying a rodent bait as defined in claim 13, for consumption by the rodents.

15. Use of an alcohol for killing rodents.

16. Use of a rodenticidal composition as defined in any of claims 1 to 12 as a rodenticide or rodent bait.