WO2007071990A1

WO2007071990A1 - An emanating device

Info

Publication number: WO2007071990A1
Application number: PCT/GB2006/004803
Authority: WO
Inventors: Benjamin David Hindle
Original assignee: Reckitt Benckiser (Australia) Pty Limited
Priority date: 2005-12-21
Filing date: 2006-12-20
Publication date: 2007-06-28
Also published as: GB0525981D0

Abstract

The inventor has found that a satisfactory rate of emanation of an active ingredient can be achieved in an emanating device having a reservoir by providing a treated wick which comprises a concentration of active ingredient that is greater than a concentration of the active ingredient held in the reservoir. The inventor has found that the invention is suitable for use with active ingredients having high, medium or low volatility. Preferred embodiment: Wick-type insecticide dispenser comprising an insecticide-impregnated upper wick portion, a reservoir for an insecticide solution (e.g. pyrethroid) wherein the lower end of the wick is dipped. The concentration of insecticide at the upper wick portion is higher than the one in the solution to ensure rapid and constant insecticide emanation.

Description

AN EMANATING DEVICE

FIELD OF THE INVENTION

The present invention relates to vapour emanating devices, and in particular to emanating devices suitable for use with low to medium volatile materials such as low to medium volatile insecticides.

DESCRIPTION OF THE RELATED ART 1. Background art

A variety of vapour dispensing devices are known in the art. Such devices typically comprise a reservoir and a wick which draws a volatile material from the reservoir to a dispensing area of the wick.

Vapour dispensing devices are used to dispense various volatile materials including for example fragrances, deodorisers, and insecticides. Deodoriser emanating devices typically provide a solution consisting of a volatile material, emulsifiers, alcohol and water. Insecticide emanating devices typically provide a solution consisting of a volatile active, stabilizer and paraffin type hydrocarbon solvent. Heat can be used to help dispense the volatile into the atmosphere.

The wick typically comprises a porous matrix. Some vapour dispensers are designed which have more than one porous member or matrix member for dispensing multiple fragrances and others comprise fragrances in predetermined ratios to ensure that each of the fragrances emanate at the same rate.

One problem with many devices is that they do not provide satisfactory emanation or they take an undesirable period of time before emanation reaches a satisfactory rate. Also, some fragrances do not emanate evenly. In some devices the emanation rate becomes so minimal that it is virtually ineffective. In the case of less volatile materials such as low volatile insecticides, these problems can be more pronounced, and some low volatile pyrethroids even initially suffer from zero or very low efficacy. Accordingly, these low volatile pyrethroids are not suitable for use in vapour dispensing devices as they take days before enough insecticide is released to be efficacious. 2. General

As used in the specification and claims, the singular form "a," "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a solvent" includes a plurality of solvents, including mixtures thereof.

A "composition" is intended to mean a combination of active agent and another compound or composition, inert (for example, an excipient) or active, such as additional insecticides.

Unless the context requires otherwise or specifically states to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.

The embodiments of the invention described herein with respect to any single embodiment shall be taken to apply mutatis mutandis to any other embodiment of the invention described herein.

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated step or element or integer or group of steps or elements or integers but not the exclusion of any other step or element or integer or group of elements or integers.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

The present invention is not to be limited in scope by the specific examples described herein. Functionally equivalent products, compositions and methods are clearly within the scope of the invention, as described herein. SUMMARY OF THE INVENTION

In work leading to the present invention, the inventor sought to provide an emanating device suitable for dispensing an active ingredient having a low, medium or high volatility. To this end the inventor developed a wick which comprises a volatile material comprising said active ingredient, the wick being suitable for use in an emanating device, in particular in an emanating device comprising a reservoir.

The inventor has found that a satisfactory rate of emanation of an active ingredient can be achieved in an emanating device having a reservoir by providing a treated wick which comprises a concentration of active ingredient that is greater than a concentration of the active ingredient held in the reservoir. The inventor has found that the invention is suitable for use with active ingredients having high, medium or low volatility.

Accordingly, in a first aspect the present invention provides a treated wick suitable for use in an emanating device having a reservoir adapted to contain a first volatile material which comprises a first concentration (0-2.5% w/w) of an active ingredient, the wick comprising a second volatile material and a second concentration of active ingredient that is greater than the first concentration of the active ingredient held in the reservoir.

In a second aspect the present invention provides an emanating device which comprises (i) a reservoir adapted to contain a first volatile material which comprises a first concentration (0-2.5% w/w) of an active ingredient and (ii) a treated wick comprising a first end immersed in said first volatile material in said reservoir and a second end not immersed in said first volatile material, said second end of the wick comprising a second concentration of the active ingredient that is higher than the first concentration.

Preferably, the first volatile material comprises a solvent. Preferably the second volatile material comprises said solvent. Preferably the active ingredient is less volatile than the solvent.

Preferably the active ingredient is an insecticide. Preferably the insecticide comprises one or more pyrethroids. In a third aspect the present invention provides a method for preparing an emanating device comprising a wick having a first end and a second end, and a reservoir adapted to contain a first volatile material which comprises an active ingredient at a first concentration (0-2.5% w/w), the method comprising treating at least the second end of the wick with a second volatile material and the active ingredient at a second concentration which is greater than the first concentration, and immersing the first end of the wick in the first volatile material held in the reservoir.

The terms "treat", "treated" and "treating" refer to the preparation (of a wick) by, for example, impregnating, soaking, incubating, painting, dipping or coating the wick or at least the second end of the wick with the volatile material for a suitable time and under suitable conditions to provide the wick with the desired concentration of the active ingredient. A combination of these treatments is within the scope of the invention.

In a preferred embodiment, the method comprises treating the length of the wick with the second volatile material. Preferably, the wick is treated by, for example, soaking, immersing or incubating the wick (or part thereof) in the second volatile material.

Preferably, the treated wick provides a suitable emanation rate in a shorter period of time than an untreated wick. Preferably, the treated wick provides a suitable emanation rate in less than 24 hours, more preferably less than 12 hours, more preferably less than 8 hours, and more preferably less than 4 hours.

In one alternative embodiment, the method further comprises drying the wick. In one embodiment, the wick is treated and dried before the wick is immersed in the volatile material in the reservoir.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a graph of the migration of bifenthrin from a doped wick into solvent.

Figure 2 is a graph of the rate at which equilibrium is reached between the wick and the reservoir.

Figure 3 is a table (Table 1) of the bio-efficacy of LED's of the present invention. Figure 4 is a table (Table 2) of "Practical volatility" of pyrethroids.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a wick comprising a volatile material which comprises an active ingredient suitable for use in a vapour emanating device.

The invention also provides an improved vapour emanating device comprising a reservoir and a wick that comprises a volatile material. Preferably the reservoir also comprises an amount of a volatile material.

The wick

Preferably, the wick comprises a porous material. A wide range of porous materials are suitable for the invention including, for example, sintered plastics, sintered carbon, glass-sintered fibres, wood, compressed wood composites, activated charcoal, cellulose, pulp, natural fibres (cotton, linen), synthetic fibres (nylon, polyester, rayon etc.), ceramic of clay materials such as gypsum, bentonite, kaolin, talc, diatomaceous earth, pearlite, alumina, silica, silica alumina and titanium.

The wick comprises a first end and a second end. The first end of the wick is immersed in the first volatile material in the reservoir which optionally comprises an active ingredient at the first concentration. The second end of the wick is not immersed in the first volatile material in the reservoir.

Further, the second end of the wick comprises a dispensing portion, i.e., a portion of the wick from which the volatile ingredient dispenses or emanates. In one embodiment, the dispensing portion is at or near the tip of the second end of the wick. In another embodiment the dispensing portion comprises all or part of the surface area of the wick that is not immersed in the reservoir.

In one embodiment the emanating device comprises a dispensing facilitator such as for example a heating means or fan which is suitable for increasing the rate of dispersion of the active ingredient from the dispensing portion of the wick.

Volatile material The first and/or second volatile material comprises an active ingredient which has a low, medium or high volatility. A wide range of active ingredients are suitable for use in the present invention. In one preferred embodiment, the active ingredient is efficacious against mosquitoes.

In one embodiment, for example, the active ingredient comprises one or more pyrethroids. In a preferred embodiment the pyrethroid is a low or medium volatile pyrethroid. Some examples of low volatile pyrethroids are permethrin, cypermethrin, cyfluthrin and deltamethrin. Some examples of medium volatile pyrethroids are bifenthrin, d-phenothrin, imiprothrin and prallethrin. In a preferred embodiment the active ingredient comprises bifenthrin. Alternatively, some examples of pyrethroids which are highly volatile are metofluthrin, transfluthrin, allethrin (series), bioresmethrin, cyphenothrin, empenthrin.

One advantage of the present invention is that low and medium pyrethroids or mixtures thereof are suitable for use in the invention.

Preferably the active ingredient is an insecticide which comprises good bite inhibition (see examples). Most preferably the insecticide provides at least 70% more preferably, 80% and more preferably 90% bite inhibition.

Preferably the insecticide comprises good knock-down and kill (mortality) capabilities for flying and/or crawling insects. Preferably the insecticide in the emanation device provides greater than 30% knockdown and/or greater than 30% mortality. More preferably the active ingredient in the emanation device provides greater than 40% knock down and/or greater than 50 % mortality. Most preferably the active ingredient in the emanation device provides at least 50% knockdown and mortality.

According to the present invention, the reservoir containing the first volatile material optionally comprises the active ingredient at a first concentration and the wick which has a first end and a second end comprises a second volatile material comprising the active ingredient at a second concentration at the second end of the wick. The second concentration of active ingredient is greater than the first concentration of active ingredient.

Preferably the second concentration of the active ingredient is 10-180mg/cm³, preferably 15-160mg/cm³, more preferably 20-140 mg/cm³, more preferably 25-120 mg/cm , more preferably 30-lOOrng/cm and more preferably about 40, 50, 60, 70, 80, 90, 100, 120, or 130 mg/cm³ and most preferably 60 or 80 mg/cm³.

The first concentration is 0-2.5% (w/w) active ingredient (i.e. % active ingredient in the volatile material in the reservoir). It is understood therefore that the reservoir can contain only solvent at the time the first end of the wick is immersed. Migration of active ingredient from the immersed portion of the wick, into the volatile material, i.e., solvent, in the reservoir will occur over time and an equilibrium is expected to eventually be reached.

Preferably the first concentration comprises 0.5-2% (w/w) active ingredient, more preferably 0.6-1.5% (w/w) active ingredient, more preferably 0.7-1.2% (w/w) active ingredient, most preferably 0.9-1.2% (w/w) active ingredient.

The concentration of active ingredient in the reservoir can be varied depending on the total volume and the amount of solvent held by the reservoir.

Solvent and other ingredients

In one embodiment the volatile material further comprises a solvent. In one embodiment the solvent is a hydrocarbon solvent. Preferably, the solvent has a boiling point in the range between about 33-285⁰C₅ more preferably, about 50-265⁰C.

The solvent may be selected from, but not limited to, any one or more of the following: chlorinated hydrocarbons (e.g. 1,1,1-trichloroethane, dichloromethane, chloroform); alcohols (e.g. methanol, ethanol, n-propanol); ketones (e.g. acetone); alcohol and ketone mixtures (e.g. acetone/ethanol (1:1 by volume)); normal paraffins with a boiling point range of about 155-276°C (e.g. Norpar™ 12); dearomatised aliphatic hydrocarbons and their blends in the boiling point range of about 33-265°C (e.g. pentane, heptane, hexane, Exxsol™ D40, Exxsol™ D80 and Exxsol™ DlOO); isoparaffϊns in the boiling point range of about 150-285⁰C (e.g. Isopar™ G, and Isopar™ M); glycol ethers in the boiling point range of about 120-243⁰C; natural or synthetically derived aroma chemicals.

Preferably the active ingredient is less volatile than the solvent. In other embodiments of the invention the volatile material further comprises any one or more of the following: dyes, fragrances and preservatives.

Fragrances which are suitable for use in vapour dispensing devices are well known and include both natural and synthetically derived aroma chemicals. Preferably the fragrance has a boiling point range of about 60-250⁰C (e.g. monoterpenes and sesquiterpenes, including monoterpene and sesquiterpene alcohols, aldehydes, ketones, esters, oxides and hydrocarbons such as linalool, geraniol, citronellal, citral, geranial, menthone, linalyl acetate, bornyl acetate, 1,8-cineole and limonene); and essential oils. The term "essential oils" refers to a volatile and aromatic liquid which is isolated by a physical process from an odoriferous plant of a single botanical species. The oil bears the name of the plant from which it is derived; for example rose oil or lavender oil. These essential oils obtained from plants may be extracted by distillation, steam distillation, expression or by extraction with fats or organic solvents.

In one preferred example of the invention the volatile material comprises, bifenthrin (active), Sudan Blue (dye), Butylated Hydroxy Toluene (antioxidant), and hydrocarbon solvent.

Preparing the wick

The wick can be prepared by a number of means. For example in one embodiment the wick is dipped in a solution of the second volatile material comprising the active ingredient and a solvent. This can be achieved by means such as by soaking the wicks (for example in a chip fryer) in a solution of the second volatile material comprising the active ingredient for up to about 24 hours, then removing the wick. One option is to allow the wick to partially or completely dry. In one embodiment the process of drying the wick will remove the solvent. The concentration of active in the solvent is calculated according to the volume of solvent that can penetrate into the wick either in total or within a specified time frame. It is not essential to fully wet the wick.

The wick can be prepared such that one or more parts of the wick or all of the wick is treated with the second volatile material. The second volatile material used to treat the wick comprises an amount of active ingredient that is greater than the concentration of active ingredient held in the reservoir. In another embodiment, the active ingredient is mixed with clay powders (e.g. blends of diatomarήaceous earth, pearlite, charcoal and wood powder). The active ingredient can be a liquid or waxy solid in which case it may need to be milled with a small amount of clay powders to make a flowable pre-mix. This premix is then blended with the clay powder to ensure even distribution prior to mixing in the necessary water volume to form a paste. The paste is then extruded, cut and dried to form the wick(s).

In another embodiment the wick is prepared by dipping the second end of the wick into a solution of the second volatile material after the first end of the wick has been placed into the reservoir. This can be achieved by inverting the reservoir and passing the second end of the wick through a solution of volatile material with the concentration of active ingredient calculated so that the required mg of active ingredient is contained in the volume of solvent measured to be absorbed into the wick during the time it is in contact with the second volatile material.

Alternately in another embodiment, the second end of the wick can be dipped prior to insertion of the first end into the reservoir,

In yet another embodiment, the wick is treated by painting or otherwise applying a very concentrated or even "pure" i.e 100% amount of active ingredient onto the second end and preferably the tip of the wick. The required amount (mg) of active ingredient can be dissolved in a solvent or other ingredient(s) and applied by printing, spraying or contacting the surface of the wick. In these cases very little active might penetrate into the wick however the necessary amount would preferably be present on the surface of the wick at start up to ensure rapid initial action.

Some pyrethroids melt at temperatures above about 66⁰C (e.g. bifenthrin) and others such as metofluthrin are liquid at room temperature and accordingly they can also be applied as a molten liquid to the very top of the wick using for example a hot glue type gun application and using, for example, calibrated dosing equipment. A wick can also be made with a hollow in the second end to facilitate this method.

In one embodiment the solvent is substantially removed from the wick. In one embodiment the solvent is removed by drying. Preferably the solvent is removed before the first end of the wick is inserted into the reservoir. An amount of volatile material in the first end of the wick (that part immersed in the volatile material of the reservoir) will leach back into the reservoir until equilibrium is reached. Preferably this does not however affect the concentration in the second end of ^• the wick, which comprises the active ingredient at a higher concentration than the concentration of active ingredient in the reservoir.

The reservoir (which may be sold as a refill) is generally in the form of a bottle made from either glass or plastic (e.g. aPET, nylon, PVC or any number of other suitable materials compatible with the active ingredient and solvents). It could however take any form such as that of a tube. Preferably the reservoir is designed to be removeably fixed into an electrical device by means of clips or a screw thread on the top of the reservoir. The wick preferably extends through the top of the reservoir and may be moulded into the reservoir or held in place by means of a gasket or stopper. Preferably, the wick is well sealed to prevent loss of solvent from the reservoir during storage. The reservoir may also have a small vent hole to prevent the build-up of a vacuum as it empties during use. This hole will be sealed in storage, usually by means of a removable cap over the wick which serves to protect the wick from breakage, to prevent consumer contact as well as sealing the vent hole, until placement in the electrical device.

EXAMPLES

Test data

(i) Equilibrium levels study

Three emanation devices were prepared containing (i) 0.7% bifenthrin in solution, (ii) 1.2% bifenthrin in solution and (iii) 2.0% bifenthrin in solution, respectively.

The emanation device comprising 0.7% bifenthrin in solution had a "plain" wick i.e the wick was not treated with any active ingredient prior to immersion in the reservoir. In order to avoid adding another 20 cycles to the time needed to reach equilibrium, the emanation devices comprising 1.2% and 2.0% bifenthrin were treated with 50 mg of bifenthrin per wick prior to starting the trial.

The trial was run until the amount of active ingredient in the second end of the wick reached equilibrium or for up to 40 cycles. One cycle equalled one eight hour period. The amount of active ingredient in the wick was then assayed by extracting the active ingredient and analysing using gas chromatography (mg in total wick). The point at which equilibrium is reached discloses the point at which the rate of emanation is equal to the rate at which the active ingredient is drawn up the wick.

Referring to Figure 1, in the reservoir comprising 0.7% bifenthrin, the amount of bifenthrin in the wick increased for about 20-25 cycles to an amount of about 38-40 mg of bifenthrin in the tip of the wick. In the emanating device having a reservoir comprising 1.2% bifenthrin, the wick was pre-doped with 50mg bifenthrin and the amount of bifenthrin increased for about 15-20 cycles until the wick contained about 80mg bifenthrin. In the emanating device having a reservoir comprising 2% bifenthrin, the wick was treated with 50mg bifenthrin and the amount of bifenthrin increased in the wick for about 35 cycles until the wick comprised about 140 mg bifenthrin.

(ii) Migration of active from wick

Wicks were treated with 50mg bifenthrin and then placed in the reservoir of an emanating device containing only solvent. Over 35 days of shaking at ambient temperature the amount of active was analysed in the immersed and non-immersed portions of the wick as well as the solvent in the bottle. Referring to Figure 2 the results indicate that the active was being leached from the bottom of the wick into the solution in the reservoir for 15-20 days, while no active ingredient appeared to be leached from the top of the wick.

(iii) Bio-efficacy Two trials for bio-efficacy were conducted against the Dengue mosquito (Aedes aegyptϊ) using standard protocols in 20 m³ chambers at Agrisearch Services Pty Ltd, Gosford, Australia. The studies were conducted in a ventilated test chamber (20 cubic metres) at a temperature of between 27.5°C and 29.5°C. The relative humidity was ambient and ranged from 40% to 79%. A positive air flow of 0.4 metres/second was generated into the chamber and air was passively vented from the chamber.

The emanation devices from the "Equilibrium levels study" (i) described herein above were tested after reaching equilibrium. Table 1 (Figure 3) provides the results. The results are an amalgamation of the two separate trials. Mixed sex adult 7 to 10 day old Dengue mosquitoes (Aedes aegyptϊ) were used in these studies. There were 50 female mosquitoes released per replicate and a variable number of male mosquitoes. The mosquitoes were collected and temporarily immobilised using carbon dioxide. Male and female mosquitoes were added to a container until 50 female mosquitoes were obtained. Because only female mosquitoes bite human subjects, the number of males present in each trial was irrelevant. The mosquitoes were allowed to recover for at least one hour before being used for testing.

The liquid electrical devices were pre-heated for 30 minutes prior to placing on the floor in the test chamber. Five minutes later mosquitoes were brought into the chamber and released. The devices continued to operate during the assessments and were stopped at the completion of the test period. Starting from 10 minutes after the mosquitoes were released, an assessment was made by one human subject of the mosquito landings and bites over a 5 minute period. Whilst seated in the chamber, the subject recorded the total number of females that initiated a bite on the subject's legs, as well as the number of females that landed without initiating biting. Mosquitoes were permitted to probe the subject but not permitted to bite the subject, and were chased away prior to this occurring.

Immediately after the 5 minute assessment period, the number of knocked down mosquitoes was recorded. All the mosquitoes were collected and removed from the chamber. After 24 hours, the number of dead mosquitoes was recorded. The same human subject was used for all assessments. Each treatment, including untreated controls was replicated five times.

Table 3 shows percentage landing inhibition, percentage bite inhibition, percentage knockdown and percentage mortality for each treatment used in the trials after 15 minutes exposure of the Aedes aegypti mosquitoes to each treatment.

Percentage landing inhibition refers to the number of mosquitoes which landed on the subject in the absence of any treatment (untreated control), minus the number of mosquitoes which landed on the subject in the presence of an LED treatment, divided by the number of mosquitoes which landed on the subject in the absence of any treatment, expressed as a percentage. Landing inhibition was assessed from 10 to 15 minutes exposure of the Aedes aegypti mosquitoes to each LED treatment. Percentage bite inhibition refers to the number of mosquitoes which probed or attempted to bite the subject in the absence of any treatment (untreated control), minus the number of mosquitoes which attempted to bite the subject in the presence of an LED treatment, divided by the number of mosquitoes which attempted to bite the subject in the absence of any treatment, expressed as a percentage. It will be appreciated that, as mosquitoes must first land before attempting to bite, of necessity, percentage bite inhibition will always be higher than or equal to percentage landing inhibition. Bite inhibition was assessed from 10 to 15 minutes exposure of the Aedes aegypti mosquitoes to each LED treatment.

Knockdown refers to mosquitoes present on the floor of the chamber after the 15 minute trial, which were either dead, moribund, or incapacitated (i.e. unable to fly off the floor of the chamber). Percentage knockdown refers to the number of knocked down mosquitoes on the floor of the chamber after 15 minutes, divided by the total number of mosquitoes present in the chamber, expressed as a percentage.

Mortality refers to the state of mosquitoes which 24 hours post-treatment were dead or completely non-responsive to prodding. Percentage mortality refers to the number of dead mosquitoes 24 hours post treatment, divided by the total number of mosquitoes collected from the chamber, expressed as a percentage.

As shown in Figure 3 the inventor found that the emanation device comprising 0.7% bifenthrin in solution and 40mg bifenthrin in the second end of the wick only provided 34 % knockdown and 18.2% mortality. By contrast the emanation device comprising 1.2% bifenthrin in solution and 80 mg bifenthrin in the second end provided 57.5% knockdown and 56.0% mortality. The emanation device comprising 2% bifenthrin in solution and 140 mg bifenthrin in the second end of the wick provided 49.9% knockdown and 69.7% mortality.

The controls included an emanation device comprising a reservoir holding 2.6% EBT (Esbiothrin).

Biological performance

To test the biological performance at various times during operation in comparison to a non-treated wick the above bio-efficacy method is used. Unused refills are placed in heater devices which are allowed to pre-heat for 30 minutes prior to introduction into the chamber. Five minutes later mosquitoes are introduced to the chamber and ten minutes later their biting/landing activity is assessed for five minutes. Percent knockdown is assessed at the end of this time and mosquitoes are collected and monitored for 24 hours to determine % mortality.

This procedure is repeated with refill bottles "aged" on heaters for the required number of use cycles (8 hours per cycle) before retesting according to the same protocol. An appropriate test cycle for a 45 night product is at initial start up, after 8 hours heating then after 7 x 8 hr cycles and 45 x 8 hour cycles.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1.. An emanating device which comprises (i) a. reservoir adapted to contain a first volatile material which comprises an active ingredient at a first concentration (0-2.5% w/w) and (ii) a treated wick comprising a first end immersed in said volatile material in said reservoir and a second end not immersed in said volatile material, said second end of the wick comprising a second concentration of the active ingredient that is higher than the first concentration.

2. The emanating device according to claim 1 wherein the volatile material comprises a solvent.

3. The emanating device according to claims 1 or 2, wherein the second concentration of the active ingredient is 10- 180 mg/cm³.

4. The emanating device according to claim 3, wherein the second concentration of the active ingredient is 60 or 80 mg/cm³.

5. The emanating device according to any one of claims 1-4 wherein the first concentration of active ingredient is 0.5-2% w/w.

6. The emanating device according to claim 5 wherein the first concentration of active ingredient is 0.7-1.2% w/w.

7. The emanating device according to any one of claims 1-6 wherein the active ingredient is a pyrethroid.

8. The emanating device according to claim 7 wherein the pyrethroid comprises bifenthrin, prallethrin or a combination thereof.

9. A treated wick, which is adapted for use in an emanating device having a reservoir adapted to contain a first volatile material which optionally comprises a first concentration (0-2.5%w/w) of the active ingredient, the wick comprising a second volatile material which comprises a second concentration of an active ingredient that is greater than the first concentration of active ingredient in the reservoir.

10. A method for preparing an emanating device comprising a wick having a first end and a second end, and a reservoir adapted to contain a first volatile material which optionally comprises an active ingredient at a first concentration (0-2.5% w/w), the method comprising treating at least the second end of the wick with a second volatile material and the active ingredient at a second concentration which is greater than the first concentration, and immersing the first end of the wick in the volatile material held in the reservoir.

11. The method according to claim 10, wherein the treated wick is dried before being partly immersed in the volatile material in said reservoir.