WO2004010783A1

WO2004010783A1 - Insect repellant

Info

Publication number: WO2004010783A1
Application number: PCT/AU2003/000945
Authority: WO
Inventors: George John Orban; John Alexander Staton
Original assignee: George John Orban; John Alexander Staton
Priority date: 2002-07-29
Filing date: 2003-07-25
Publication date: 2004-02-05
Also published as: AU2002950436A0

Abstract

The invention relates to insect repellent compositions which are free from N-N-diethyl-m-toluamide (DEET). The insecticides are based around compositions of one or more essential oils, and are effective against mosquitoes, flies, sandflies, leeches fleas and ticks. Particularly preferred compositions include synergistic mixtures of two essential oils. Most preferably, the compositions are mixtures of backhousia citriodora oil and melaleuca ericafolia oil. It has also been found that adding film-formers to the present invention maintains the efficacy for around two hours at levels which are compatible to commercial DEET formulations.

Description

TITLE: INSECT REPELLANT TECHNICAL FIELD

The invention relates to insect repellents, in particular to personal insect repellent products based on natural essential oils. BACKGROUND ART

The unpleasant and annoying effect which flies, mosquitoes and other insects can have on outdoor activities such as picnics and the like is well known. However, the effects of insect bites extend beyond being a mere annoyance.

Insects can transmit disease by contact with humans and human food. The ability of flies to transmit bacteria is well known. Of particular concern are the diseases communicated by mosquitoes. Mosquitoes drink mammalian blood from a variety of species, including humans and move from host to host. Thus, as well as causing irritating and often painful bites when they drink the blood of human hosts, mosquitoes have the ability to transmit viral particles into the human blood stream. The most serious pathological conditions transmitted by mosquito include malaria, yellow fever, lyme disease, and in particular in Australia the Ross River virus (Epidemic Polyarthritis), Dengue fever, and Murray Valley encephalitis.

All of these conditions can be potentially serious and even life threatening, and mosquito-borne illnesses are responsible for thousands of deaths worldwide every year.

Clearly, the preferred method of preventing access to the human skin by mosquitoes and other insects is the use of physical barriers such as heavy clothing, nets, fly screen doors and the like. hi some circumstances, it is possible to clear insects from enclosed spaces by the use of "knockdown" insecticidal compositions, insecticidal baits which attract and poison or entrap insects, or by devices such as UN lamps which attract and electrically destroy insects. However, under circumstances where people are travelling, working, playing sport or relaxing outdoors, the use of physical barriers to avoid insect bites is impracticable and, aside from continual swatting and the like, the main means of repelling insects is to use personal insect repellent compositions. To obtain maximum effect, these compositions are generally applied directly to the skin. ' The most commonly used active in personal insecticide compositions is Ν,Ν- diethyl- -toluamide (DEET). DEET has been used for around 50 years and is regarded as the industry standard in personal insect repellents. DEET is usually used in personal repellent products at compositions of around 15-20 wt% of the total mixture. DEET is highly effective and has a long retention time on the skin. DEET however suffers from some disadvantages in that it is known to be aggressive to plastics and under some circumstances can cause irritation of the skin, and even more particularly, the eyes and mucus membranes. DEET also leaves a somewhat sticky, greasy feel on the skin. h recent years, there have been toxicity concerns raised in relation to the use of DEET.

Some efforts have been expended to find alternatives to DEET. One of these alternatives is picaridin, which has been shown to be efficacious in repelling insects. However, because it is a synthetic compound it may be perceived by some sectors of the community as being less desirable than those compounds based on natural materials.

Natural materials such as unrefined essential oils have been used from time to time as insect repellents. The most common among these are, for example citronella and limonene. However, essential oils are known in the art to provide generally low levels of insect repellency and, more importantly, because they are highly volatile, are known to be unsuitable because of their lack of long-term efficacy, especially where they are spread thinly on warm human skin and exposed to the elements, where rapid evaporation would be expected. Even as recently as July 2002, it was reported (N. Eng. J. Med., Vol. 347, No.l, p. 13) that currently available non-DEET repellents (including, inter alia, a number of essential oils) do not provide protection for durations similar to those of DEET-based repellents and cannot be relied on to provide prolonged protection in environments where mosquito borne diseases are a substantial threat. Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Accordingly, it is object of the present application to overcome one or more of the above disadvantages or at least to provide an alternative repellent formulation to those already available.

DESCRIPTION OF THE INVENTION

According to a first aspect, the invention provides an enduring N,N-diethyl- - toluamide free insect repellent composition including an essential oil or a combination of two or more essential oils as an active insect repelling agent. The compositions are especially suited to personal skin application. By enduring, it is meant that the insect repellent is efficacious for a time compatible with N,N-diethyl- -toluamide (DEET).

Preferably and more specifically, the enduring composition has repellency after two hours of at least 90% and more preferably at least 95% of the initial repellency at the time of application.

It is also preferable that the enduring composition has an initial efficacy of at least 90% that of DEET, and more preferably, an initial efficacy of at least 95% that of DEET. Preferably, the essential oil is selected from the group consisting of backhousia citriodora oil, melaleuca ericafolia oil, callitrus collumellaris (leaf) oil, callitras glaucophyla oil, melaleuca linarifolia oil and combinations thereof. Most preferably the essential oil is backhousia citriodora oil or melaleuca ericafolia oil, or even more preferably, the essential oil is a mixture of backhousia citriodora oil and melaleuca ericafolia oil. If a mixture of oils is used, preferably the oils are selected on the basis of complementary activity profiles as displayed over a period of about two hours.

The essential oil or mixture of oils may be present in the repellent composition in any amount. Preferably, the essential oils alone or in combination are present in an amount of up to 20% wt/wt, or more preferably up to 10% wt/wt. If the essential oil is backhousia citriodora oil, it is preferably present in an amount of up to 4%, and more preferably around 1-2%. If the oil is melaleuca ericafolia oil, it is preferably present in an amount of up to 8%, and more preferably around 2-4%. Most preferably, the invention provides an insect repellent including a blend of melaleuca ericafolia oil and backhousia citriodora oil. The ratio of melaleuca ericafolia oil to backhousia citriodora oil is preferably between 10:1 and 1:10, and more preferably between 2:1 and 4:1. The above preferred ratios were found to provide the best combination for the above two compounds. The individual oils have different fractions which evaporate at different rates. The melaleuca ericafolia oil, for instance, is believed to provide most of the repellency in the initial stages, while the backhousia citriodora oil provides a higher contribution to the repellency after about the first hour. Where the embodiments of the present invention relate to the use of gels or creams, those skilled in the art will appreciate that where unstated, the percentages referred to are %wt/wt. Where the formulations are sprayable, the formulation is %wt/volume.

As mentioned above, essential oils have generally been considered to be unsuitable as insect repellents because of their inherently high volatilities and low efficacies after relatively short periods of time. Individuals are generally unwilling or unable to reapply insect repellents repeatedly after only short time intervals. Surprisingly, in the present invention, it has been found that selected essential oils exhibit durations of action which render them commercially useful as insect repellents. Further, by combining specific essential oils, it is possible to extend the efficacy of the combination over a longer duration of action than would be expected from the individual oils alone. Essential oils are a complex blend of organic compounds, sometimes containing up to several hundred component compounds. The oils used in the present invention typically contain around fifteen different compounds.

Essential oils contain a vast array of compounds of different structural classes including aldehydes (eg citronellal), cyclic alkenes (eg pinene, phellandrene), aromatic hydrocarbons (eg p-cymene), phenols( eg p-isopropylphenol), aromatic aldehydes (eg cuminal) and epoxides (eg eucalyptol ).

Thus, unlike a single pure compound, an essential oil may have a unique evaporation profile, with some compounds evaporating more rapidly than others. Once exposed to skin and air, an essential oil composition does not merely evaporate like a homogenous compound, but changes in composition and efficacy as it does so. It is possible in some cases that one or more rapidly evaporating components of the essential oil mask more efficacious, less volatile components, so in some instances, efficacy in repelling insects may actually rise at some points in the evaporation profile.

The possibility also exists of chemical changes within the oil. Some essential oil components are functionalised, for instance with carbonyl groups or hydroxyl groups, and so may be capable of reaction with the skin of the subject (normal skin is usually slightly acidic). While individual essential oils are usually chemically stable, this does not preclude the possibility of reaction between components in two or more essential oils, and more importantly, it does not preclude the possibility of hydrogen bonding (or other types of non bonded interactions) between components, which is likely in the case of groups bearing oxygen functionalities. Such non-bonded interactions are complex and lead to the oil behaving differently from the sum of its constituent parts. When two or more oils are mixed, there exists the possibility of different types of interaction so a combination of oils may again behave differently from each of the starting oils. Preferably, the enduring insect repellent further includes an agent adapted to enhance the insect repellency after two hours of the composition relative to the efficacy of the essential oil or oils alone. Most preferably, the enhancement is synergistic. Examples of agents adapted to enhance the insect repellency include film formers, hydrocarbons or fatty acids of hydrocarbons. Any suitable film former may be used. Those examples of film formers which are particularly useful are those film formers used in sunscreen formulations as barriers to prevent water from deactivating the active agents. Examples of film formers include PVP; PVP/hexadecene, PVP/eicosene copolymers (such as are sold under the trade name Antaron), trimethylpentanediol adipic acid/isononanoic acid copolymers (such as are sold under the trade name Lexorez TC8), trimethyl pentanediol/adipic acid/glycerin crosspolymers (such as are sold under the name Lexorez 200) or polycarbamyl polyglycol esters (such as are sold under the trade name Pecogel). C10-C12 fatty acids are suitable for use in the present invention. Other film formers may include poly( vinyl pyrrolidone/1-triacontene) acrylate copolymers, acrylate/octylacrylamide copolymers, acrylate/VA copolymer, amodimethicone, AMP/acrylate copolymers, behenyl beeswax, behenyl/isostearyl, beeswax, butylated PVP, butyl ester of PVM/MA copolymers, calcium/sodium PVM/MA copolymers, dimethicone, dimethicone copolyol, dimethicone/mercaptopropyl methicone copolymer, dimethicone propylethylenediamine behenate, dimethicolnol ethylcellulose, ethylene/acrylic acid copolymer, ethylene/MA, copolymer, ethylene/NA copolymer, fluoro C2-8 alkyldimethicone, hexanediol beeswax, hydrogenated styrene/butadiene copolymer, hydroxyethyl ethylcellulose, isobutylene/MA copolymer, laurylmethicone copolyol, methyl methacrylate crosspolymer, methylacryloyl ethyl betaine/acrylates copolymer, microcrystalline wax, nitrocellulose, octadecene/MA copolymer, octadecene/maleic anhydride copolymer, octylacrylamide/acrylate/butylaminoethyl methacrylate copolymer, oxidized polyethylene, perfluoropolymethylisopropyl ether, polyacrylic acid, polyethylene, polymethyl methacrylate, polypropylene, polyquaternium-10, polyquaternium- 11 , polyquaternium-28, polyquaternium-4, PVTVI/MA decadiene crosspolymer, PVM MA copolymer, PVP/decene copolymer, PVP/MA copolymer, PVP/VA copolymer, silica, silica dimethyl silylate, sodium acrylate/vinyl alcohol copolymer, stearoxy dimethicone, stearoxytrimethylsilane, stearyl alcohol, stearylvinyl ether/MA copolymer, styrene/DVB copolymer, styrene/MA copolymer, tetramethyl tetraphenyl trisiloxane, tricontanyl trimethyl pentaphenyl trisiloxane, trimethylsiloxysilicate, VA/crotonates copolymer, VA/crotonates/vinyl propionate copolymer, VA/butyl maleate/isobornyl acrylate copolymer, vinyl caprolactam PVP/dimethylaminoethyl methacrylate copolymer, vinyldimethicone and the like. The insect repellents of the present invention may be formulated in any known carrier system. Preferably, the repellents are formulated as gels, creams (two phase systems), lotions (thinned creams or aqueous alcohols) or spray on formulations (usually alcohol based). Those skilled in the art will appreciate that while some forms of base are preferred, a wide variety of known standard generic and proprietary carriers may be used without departing from the concept of the present invention.

Preferably, the insect repellents of the present invention are in the form of a lotion, cream or gel. In certain preferred embodiments, the gel contains 5% PVP/eicosene copolymer.

The invention may also be in the form of a stick applicator which can be applied to the skin.

Any lotion base is suitable for the purposes of the present invention.

The gels are preferably based on avocado oil or sweet almond oil. Preferably, the gels are thickened with silica.

The bases of the present invention may also contain other ingredients and excipients, which may be physiologically inactive (such as colourants) or may have cosmetic use or otherwise act to modify the formulation property, such as waxes. The excipients may also be active agents. Examples of active agents which are particularly preferred are those which exhibit sunscreen activity.

Those skilled in the art will also appreciate that the formulations of the present invention may be formed by a variety of processes. These include hot processes (where mixing involves heating to liquefy one or more of the ingredients prior to mixing) or cold processes (where the mixing of all the ingredients is carried out without prior heating). If a hot process is used, it is preferable that the repellent oil or oil blend of the present invention is introduced after the base formulation has cooled. If a cold process is used, the repellent oil or oil blend of the present invention may be introduced at any time. Preferably, the composition is effective against mosquitoes, flies, sandflies, leeches, fleas and ticks. In particular, the repellent is efficacious against mosquitoes of the species Aedes aegypti.

The insect repellents may also be in the form of a spray, for example an alcohol based spray.

BEST MODES FOR CARRYING OUT THE INVENTION In Vitro Testing: General Protocol

The general protocol for determining Mosquito repellency in vitro is as follows.

1) 50 Female sucrose fed mosquitoes were introduced into a screened cage measuring 45 x 30 x 30cm. The cage was fitted with a clothed sleeve to allow the introduction of an arm without escape of the mosquitoes.

2) One forearm of a volunteer was left untreated and the other forearm was treated with a candidate repellent. The forearm was sprayed from distance of 15cm to give even coverage. The amount of aerosol sprayed was noted. 3) Both hands and forearms were left to dry before being covered up with long rubber gloves. The rubber gloves had a 25cm² area removed to provide exposed skin at the back of the hand to the mosquitoes. No other skin was exposed to the mosquitoes in order to prevent any unwanted bites.

4) The untreated arm was placed in the cage and was exposed for a period of 5 minutes. The number of mosquitoes landing and/or biting on the exposed skin was noted.

5) The treated arm was placed in the cage and was exposed for a period of 5 minutes. The number of mosquitoes landing and/or biting on the exposed skin was noted. 6) Steps 4 to 6 were repeated at intervals of 15, 30, 45, 60 and 120 minutes after repellent application.

The above procedure was repeated on 3 or more volunteers to give total or full replications. Percentage Repellency Of Mosquitoes At Various Times After Essential Oil Application

The efficacy of various essential oils as insect repellents was investigated. The method of testing involved placing a 2g sample of a cream containing 2 - 10% the essential oil on to the volunteer arm from the wrist to the elbow and placing into a mosquito cage as detailed above. The results given below in the table show the percentage repellency of each oil in a cream base relative to the control which is an untreated arm.

TABLE 1 Percentage Mosquito Repellency v Time for a Variety of Essential Oils

Surprisingly, it was found that some of the essential oils, especially the backhousia citriodora oil and the melaleuca ericafolia oil had retained good repellency characteristics after 120 minutes. It was believed these warranted further investigation. Other essential oils, such as Callitras collumellaris (leaf) oil, Callitras glaucophyla oil, Melaleuca linarifolia oil and Melaleuca uncinata oil were also not without promise. EFFECT OF BASE TYPE

The effect of the nature of the type of product base, ie whether the base was a cream, lotion or gel, was investigated. The percentage repellency at various times was evaluated for three different base types with four different formulations. Three of the formulations were in accordance with the present invention, being mixtures of backhousia citriodora oil and melaleuca ericafolia oil. These formulations were compared against a control formulation containing DEET. TABLE 2 Percentage Mosquito Repellency v Time for Different Base Types

The lotion base also contained 5% Diisopropyl Adipate as adjunct. Surprisingly, the natural essential oils remained more efficacious in lotion and gel bases rather than in a cream base. The 2% backhousia citriodora oil and 8% melaleuca ericafolia oil in lotion base was able to maintain an efficacy similar to that of DEET in a cream base. The gel base also appeared promising.

The percentage repellency at various times after application was measured for gel and cream bases which both contained an adjuvant, and compared against a commercially available DEET containing compound. The gel and cream bases of the present invention as tested contained 1% backhousia citriodora oil, 4% melaleuca ericafolia oil, 10% diisopropyl adipate (as adjunct) and silicon dioxide (as adjunct), 5% in the case of the gel and 3% in the case of the cream.

The commercial control contained 6.98% DEET and 2.79% Di-n- propyl isochinchomerate. TABLE 3 Percentage Mosquito Repellency v Time for Different Base Types

It can be seen from the above that while the essential oils give good initial results (even comparable to those for the DEET product) in general the degree of repellency drops quite markedly after around 30 minutes, suggesting the active is losing efficacy.

In order to further increase the efficacy of the insect repellents, the possibility was investigated of adding various agents to attempt to retard the evaporation of the oils and therefore improve product efficacy.

One class of compounds found to be effective are film-forming agents. Because it was also believed that short chain hydrocarbons may also inhibit oil evaporation, a C₁₀-C₁₂ fatty alcohol was tested as an additive.

The following table shows the effects of adding various film forming or potential evaporation retarding agents to a 4% Melaleuca Ericafolia oil + 1 % Backhousia Citriodora oil combination in a cream or gel base.

TABLE 4 Percentage Mosquito Repellency v Time for Different Film Former Types

From the above, it can be seen that the gel bases were the best, although the second and third formulations were also significantly improved in their long-term efficacy relative to the products without film formers. Given that the film formers have no intrinsic repellency properties, this clearly demonstrates a synergistic relationship between the essential oils and the film former.

The bases were further reviewed with the aim of further extending the effective repellency lifetime.

A gel based on sweet almond oil was used. The efficacy was compared with an emulsion-based formulation containing PVP/Eicosene copolymer. An alcohol based product, containing Lexorez TC8 was also tested. The alcohol based product may be useful as a sprayable repellent. TABLE 5 Percentage Mosquito Repellency v Time for Different Base Types

These results show the gel to be most effective. While the other products are not quite as effective in the enclosed test environment, it is likely that they may still be effective in the field, given the concentration of mosquitoes in the environment is much lower. It may be possible to obtain improved results by increasing the amount of essential oils for a spray, or increasing the film forming properties.

The compositions of the present invention can also be incorporated into sunscreen formulations. The introduction of sunscreen components had no effect on the insect repellency of the mixture.

The effect of varying the ratios of Melaleuca Ericafolia oil + Backhousia Citriodora oil was investigated. Changing the ratio of Melaleuca Ericafolia oil: Backhousia Citriodora oil from 4:1 to 4:2 was examined first. TABLE 6 Percentage Mosquito Repellency v Time for Different Ratios of Essential Oils for a Sprayable Alcohol Based Product.

These results showed a significant increase in the long-term efficacy of the product. Further increasing the amount of backhousia citriodoria oil from 1 to 2% had little effect in non-sprayable compositions, such as gel based or lotions. LN VITRO TESTING: HOUSE FLY REPELLENCY

The efficacy of the material as a house fly repellent (in addition to a mosquito repellent) was also investigated, using a similar protocol to the mosquito repellency tests. The formulations below were identical and were in a gel base. Both contained

4% melaleuca ericafolia oil + 1% backhousia citriodora oil, and 5% PVP/eicosene copolymer as film former. One formulation also contained other essential oils to determine if these would enhance efficacy. The results were also compared to those obtained earlier for mosquitoes. TABLE 7 Percentage Repellency for House Flies v Time and Comparison with

Mosquito Results

These results show that the formulation of the present invention is particularly effective as a fly repellent as well as a mosquito repellent. Further, it appears to suggest, in the case of the second house fly repellent, that increasing the amount of essential oils seemed not to change the efficacy of the mixture. LN VITRO TESTING: FLEAS, TICKS AND LEECHES

Each form of repellent was also tested against fleas, ticks and leeches. The gel and emulsion each contained Backhousia citriodora oil at 1% and Melaleuca ericafolia oil at 4%, with PVP/Eicosene Copolymer film former at 4% in the gel and 5% in the emulsion. The spray contained 2% Backhousia citriodora oil and 4% Melaleuca ericafolia oil with Trimethylpentanediol/ Adipic acid/Isononanoic acid copolymer film former at 5%.

The commercially available DEET containing spray used for comparison was "Off! Skintastic" ™(S.C. Johnson) which contained 6.98% DEET and 2.79% Di-n- propyl isocinchomeronate.

Note in these experiments, the application rate of the gel was half that of the other forms of repellent.

The efficacy of the products against the Cat Flea (Ctenocephalides felis) was evaluated in-vitro according to the following protocol:

1) 30 Cat Fleas were held in a tall glass beaker with a filter paper on the bottom.

2) A volunteer placed an exposed finger treated with 4 mg/cm² emulsion or spray repellent (2mg/cm² in the case of the gel repellent) inside the beaker.

3) The number of fleas jumping up to, and remaining on the finger was recorded.

4) The test was repeated with a new batch of fleas at each time point as it was observed that the products were having a knockdown effect on the fleas.

5) An untreated finger was used as a control. 6) The above procedure was repeated on 5 volunteers to give total or full replications.

TABLE 8 Percentage Repellency for Cat Fleas v Time compared to a commercially available DEET product

These results indicate that the performance of the spray and emulsion compares favourably to that of the DEET containing product. While the gel's repellency appears lower in the test environment, its performance in the field may be greater due to the reduced concentration of insects in the outdoor environment.

The efficacy of the product against the Dog Paralysis Tick (Ioxides holocyclus) was evaluated in-vitro according to the following protocol:

1) A volunteer's hand was treated with 360 mg of emulsion or spray repellent (180mg in the case of the gel repellent).

2) The hand was then placed into a dish containing 10 ticks. 3) The number of ticks crawling onto the hand after 5 seconds was then recorded.

4) An untreated hand was used as a control.

5) The above procedure was repeated on 5 volunteers, at 30 minute intervals, to give total or full replications.

TABLE 9 Percentage Repellency for Dog Paralysis Ticks v Time compared to a commercially available DEET product

These results indicate that all products are quite effective as tick repellents. It is quite likely repellency results will be even higher in the outdoor environment.

The efficacy of the products against the Leech of genus microbdella sp. was evaluated in-vitro according to the following protocol:

1) A volunteer's hand was treated with 4mg/cm² of emulsion or spray repellent (2mg/cm² in the case of the gel repellent). 2) The hand was then placed into a dish containing 10 leeches.

3) The number of leeches crawling onto the hand and remaining there after approximately 5 seconds was recorded.

4) An untreated hand was used as a control.

TABLE 10 Percentage Repellency for Leeches v Time compared to a commercially available DEET product

These results indicate that the emulsion and spray products are quite effective as leech repellents. The gel appears to have good initial repellency which tends to diminish over time. While leech concentrations in the environment may be lower, other factors such as the dampness of the environment in which they live may influence results that would be obtained in the field. In Vivo Testing: Bush Fly Repellency

A field study was carried out to compare the repellency of various insect repellents against the bush fly. The test was conducted under confidential conditions on private property in South West Queensland, where the predominant flying insect species was the bush fly (Musca Vetustissima). The test was conducted from early morning to mid afternoon in early summer, over a six-hour period. The number of insects landing was assessed at various nominated times during this period. In particular, prior to repellent application and at 15, 30, 45, 60, 90, 120, 180, 240 and 360 minutes post insect repellent application. Volunteers selected for the study were males and females between the ages of

18 and 65 years. All volunteers wore shorts to expose the lower leg below the knee. Following repellent application and between assessments volunteers were free to walk, stand or sit. The temperature was warm to hot, around 30°C, leading to volunteers sweating for much of the study period. The volunteers also walked around the property in between assessments resulting in the repellent being subjected to long grass and direct sunshine.

The repellent gel contained 4% melaleuca ericafolia oil and 1% backhousia citriodora oil and was applied at a rate of 1.8 grams per lower leg. The repellent emulsion also contained 4% melaleuca ericafolia oil and 1% backhousia citriodora oil and was applied at a rate of 3.6 grams per lower leg. The repellent spray contained 4% melaleuca ericafolia oil and 2% backhousia citriodora oil and was applied at a rate of 3.6 grams per lower leg and the commercial DEET containing formulation SC Johnson "Off Skintastic"™ Spray was applied at a rate of 3.6 grams per lower leg. Each treatment was replicated with 5 volunteers, as well as a control group of a similar size.

Each of the volunteer's legs were marked just below the knee and just above the ankle to mark the area for repellent application. The repellent was applied at the requisite rate per lower leg. To prevent contamination of the repellent of other subjects, the applicators wore disposable surgical gloves. One repellent was applied to one leg of each volunteer and one repellent was applied to the other. The repellents were allocated relatively evenly to either the right or left leg.

Before repellent application at the start of each new day of testing, a check was made that there was sufficient insect population pressure by confirming that insects landed on both untreated legs of all subjects. This also checked the inherent repellency of the test subjects to bush flies.

The limbs were exposed to bush flies for a period of 6 hours and assessed at the times as set above. A variety of base types as optimised above was used. A comparative test using a commercially available sample was also used. The landing number of flies over a ten minute period at the various times for a period greater than one second during the test duration were counted. Landings were defined as resting on the limb and not merely touching it. After the flies had settled they were disturbed by moving the limb. The above was repeated four times to complete five replicates for each formulation. TABLE 11 Percentage Repellency of Bush Flies at Various Times After Application

The results appear above. The percentage repellency helps correct for any change in insect pressure during the course of the study. The percentage repellency is calculated using the following formula:

Statistical Analysis

The difference between treatment means in the number of bush fly landings was assessed for significance using analysis of variance (Inova, SPSS version 10, 1999). Only data obtained 180 minutes and 360 minutes after the start of the trial were analysed. Data was checked for compliance with assumption of normality and variance homogeneity. Data for assessment at 180 minutes after the start of the experiments were ln(x + 1) transformed to meet later assumptions while data for assessment at 360 minutes after the start of the trial better approached assumptions without any transformation.

The analysis shows that there were significant differences between treatments for both 180 minute and 360-minute assessment times. F_{4) 0} = 10.66, PO.0001 and F_4;2o = 14.713, P<0.0001 respectively. The analysis also show that there were significant differences between all active treatments and the control at both 180 minutes and 360 minutes post repellent application. Pairwise comparison between repellent treatments and untreated control was calculated and assessed using Dunn- Sidak adjusted probabilities (the nominal probability of 5% was adjusted to 1.274 for four comparisons).

Table 12 shows a summary of the statistical analysis. The significance of differences between treatments was determined using the pairwise comparison control vs repellents. Dunn-Sidak adjusted probability was used. TABLE 12 Statistical Analysis of Bush Fly Results

S= significant at adjusted probability of 1.274%

It can be seen that the bush fly is attracted to skin, particularly after sweating. Without a repellent present, the bush fly will land on the skin and wander over the surface searching for secretions such as sweat, tears and saliva. Favourite sites include the face and the back although exposed limbs are also very attractive. When a suitable repellent is present the bush fly will come close to the skin and will then veer off or touch the skin for a fraction of a second before flying off. Each of the active treatments had a statistically significantly lower number of landings by bush flies than the control at both 180 minutes and 360 minutes after application. Control bush fly landings range from 13-74 landings in a ten-minute period on an untreated leg over the course of the study.

In a similar manner to bush flies, the efficacy of the formulations of the present invention were tested in vivo against Mosquitoes. The results in the following table show excellent efficacy for all formulations after two hours, which are comparable with DEET.

TABLE 13 Percentage Repellency of Mosquitoes in vivo at Various Times After Application

The efficacy of the present invention against biting midges (sandflies) was also tested in a similar way. The formulations were as optimised previously, and were compared against a commercial product. Again, the Gel and Emulsion fared very well. TABLE 14 Percentage Repellency for Biting Midges v Time

EXAMPLE FORMULATIONS

As mentioned above, the present invention may be used in may different bases. Examples of commercially useful bases are provided herewith for spray on use, emulsion use and as a formulation for use as a combination insect repellent/sunscreen. SPRAY ON FORMULATION (I)

EMULSION BASED FORMULATIONS (II) and (III)

SUNSCREEN/LNSECT REPELLENT FORMULATIONS (IV) AND (V)

Those skilled in the art will appreciate that compositions according to the present invention may be varied beyond those given by way of exemplification and that it may be possible to formulate other compositions in other concentrations and with other additives without departing from the inventive concept herein disclosed.

Claims

THE CLAIMS OF THE INVENTION ARE AS FOLLOWS:

1. An enduring insect repellent composition including an essential oil or a combination of two or more essential oils as an active insect repelling agent.

2. A composition according to claim 1 which is free from N,N-diethyl- - toluamide (DEET).

3. A composition according to any one of the proceeding claims having an initial repellency on application and a repellency after two hours of at least 90% of the initial repellency

4. A composition according to claim 3 wherein the repellency after two hours is at least 95% of the initial repellency at the time of application.

5. A composition according to any one of the preceding claims having an initial efficacy of at least 90% of a corresponding amount of DEET.

6. A composition according to claim 5 having an initial efficacy of at least 95% of that of a corresponding amount of DEET.

7. A composition according to any one of the preceding claims wherein the essential oil is selected from the group consisting of: backhousia citriodora oil, melaleuca ericafolia oil, callitras coUumellaris (leaf) oil, callitras glaucophyla oil, melaleuca linarifolia oil and combinations thereof.

8. A composition according to any one of the preceding claims wherein the essential oil is backhousia citriodora oil or melaleuca ericafolia oil.

9. A composition according to any one of the preceding claims wherein the essential oil is a mixture of backhousia citriodora oil and melaleuca ericafolia oil .

10. A composition according to any one of the preceding claims wherein if two or more oils are used, the oils are selected on the basis of complementary activity profiles displayed over a period of two hours.

11. A composition according to any one of the preceding claims wherein the essential oils alone or in combination are present in an amount of up to 20 wt%.

12. A composition according to any one of the preceding claims wherein the essential oils are present in an amount up to 10% wt per wt

13. A composition according to any one of the preceding claims including backhousia citriodora oil in an amount of up to 4 wt%.

14. A composition according to claim 13 including backhousia citriodora oil present in an amount of about 1-2%.

15. A composition according to any one of the preceding claims including melaleuca ericafolia oil in an amount of up to 8 wt%.

16. A composition according to claim 15 including melaleuca ericafolia oil in an amount of around 2-4 wt%.

17. A composition according to any one of the preceding claims including melaleuca ericafolia oil and backhousia citriodora oil.

18. A composition according to claim 17 including melaleuca ericafolia oil and backhousia citriodora oil in a ratio between 10:1 and 1:10.

19. A composition according to claim 18 including melaleuca ericafolia oil and backhousia citriodora oil in a ratio between 2: 1 and 4:1.

20. A composition according to any one of the preceding claims in the form of a gel.

21. A composition according to any one of claims 1 - 19 in the form of a cream.

22. A composition according to any one of claims 1 - 19 in the form of a spray.

23. A composition according to any one of claims 1 - 19 in the form of a stick applicator.

24. A composition according to any one of the preceding claims further including an agent adapted to enhance insect repellency after two hours.

25. A composition according to claim 24 wherein the agent adapted to enhance insect repellency is selected from the group consisting of film formers, hydrocarbons, or fatty acids of hydrocarbons.

26. A composition according to claim 25 wherein the agent adapted to enhance insect repellency is a film former.

27. A composition according to claim 26 wherein the film former is effective as a barrier to prevent water from deactivating the essential oil or oils.

28. A composition according to claim 26 or 27 wherein the film formers are selected from the group consisting of PVP, PVP/hexadecene, PVP/eicosene copolymers, trimethylpentanediol/adipic acid isononanoic acid copolymers, trimethylpentanediol adipic acid/glycerin crosspolymers, polycarbamyl polyglycol esters and C10-C12 fatty acids.

29. A composition according to any one of the preceding claims further including a film former selected from the group consisting of poly(vinyl pyrrolidone/1- triacontene) acrylate copolymers, acrylate/octylacrylamide copolymers, acrylate/VA copolymer, amodimethicone, AMP/acrylate copolymers, behenyl beeswax, behenyl/isostearyl, beeswax, butylated PVP, butyl ester of PVM/MA copolymers, calcium/sodium PVM/MA copolymers, dimethicone, dimethicone copolyol, dimethicone/mercaptopropyl methicone copolymer, dimethicone propylethylenediamine behenate, dimethicolnol ethylcellulose, ethylene/acrylic acid copolymer, ethylene/MA, copolymer, ethylene/VA copolymer, fluoro C2-8 alkyldimethicone, hexanediol beeswax, hydrogenated styrene/butadiene copolymer, hydroxyethyl ethylcellulose, isobutylene/MA copolymer, laurylmethicone copolyol, methyl methacrylate crosspolymer, methylacryloyl ethyl betaine/acrylates copolymer, microcrystalline wax, nitrocellulose, octadecene/MA copolymer, octadecene/maleic anhydride copolymer, octylacrylamide/acrylate/butylaminoethyl methacrylate copolymer, oxidized polyethylene, perfluoropolymethylisopropyl ether, polyacrylic acid, polyethylene, polymethyl methacrylate, polypropylene, polyquaternium-10, polyquaternium-11, polyquaternium-28, polyquaternium-4, PVM/MA decadiene crosspolymer, PVM/MA copolymer, PVP/decene copolymer, PVP/MA copolymer, PVP/VA copolymer, silica, silica dimethyl silylate, sodium acrylate/vinyl alcohol copolymer, stearoxy dimethicone, stearoxytrimethylsilane, stearyl alcohol, stearylvinyl ether/MA copolymer, styrene/DVB copolymer, styrene/MA copolymer, tetramethyl tetraphenyl trisiloxane, tricontanyl trimethyl pentaphenyl trisiloxane, trimethylsiloxysilicate, VA crotonates copolymer, VA/crotonates/vinyl propionate copolymer, VA/butyl maleate/isobornyl acrylate copolymer, vinyl caprolactam/PVP/dimethylaminoethyl methacrylate copolymer, vinyldimethicone and mixtures thereof.

30. A composition according to claim 20 when formulated as a gel containing 5% PVP eicosene copolymer.

31. A composition according to any one of the preceding claims based on avocado oil or sweet almond oil.

32. A composition according to any one of the preceding claims further including one or more agents selected from the group consisting of a thickening agent, colorant.

33. A composition according to any one of the preceding claims further including a sunscreen agent.

34. A method of repelling an insect including the steps of providing to a surface a composition according to any one of the preceding claims.

35. A method according to claim 34 wherein the surface is a human skin surface.

36. A method according to claim 34 or 35 wherein the insects are selected from the group consisting of mosquitoes, flies, sandflies, leeches, fleas, ticks and combinations thereof.

37. A method according to the preceding claim wherein the insect is a mosquito of the species aedes aegypti.