EMANATOR MATS

Abstract: Mats for use in an insecticide emanator, which contain an insecticidal composition comprising one or more pyrethroid insecticide having a vapour pressure at 25 DEG C of from 0.1 to 200 milliPascals (mPa), preferably from 0.1 to 100 mPa, especially from 1 to 50 mPa, together with piperonyl butoxide and/or one or more analogues thereof, in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1.

Description: EMANATOR MATS This invention concerns insecticide emanator mats, and insecticidal formulations for use therewith, as well as methods of combating insects using them. PRIOR ART Insecticide emanator devices are well known which comprise a heating element adapted to heat a replaceable insecticide-containing mat to a predetermined temperature, usually about 130-160°C, so as to vaporise the insecticide over a period of time, and provide protection in their vicinity, typically against mosquitos or flies. The insecticidal composition, which is often based on a pyrethroid insecticide such as allethrin, is impregnated into the mat, which usually consists of an inert porous substance such as cardboard, wood pulp fibre, textile pulp, synthetic fibres or a porous resin. However, the typical useful life of such mats is low, being of the order of just 12 hours, which means that they are rather unsuitable where prolonged insect control is required. Attempts to provide greater useful life by increasing the quantity of insecticide present in the mat have failed, apparently because the insecticide tends to degrade on prolonged heating, leading to much reduced, uneven release into the atmosphere. Most other attempts to provide longer periods of insect control have therefore not involved mats at all, but have been based on liquid formulations contained in bottles with a heated wick device to release the insecticide into the air. These, however, are bulky, breakable, and prone to leakage, with consequent uncontrolled loss of the toxic insecticide formulation. The formulations used typically contain over 95% by weight of a hydrocarbon solvent, and this is inevitably a fire hazard, which increases in proportion to the amount of formulation employed, and thus the desired useful life of the product. DESCRIPTION It is an object of the present invention to provide insecticide emanator mats which are improved relative to those available hitherto. Accordingly, in one aspect, this invention provides a mat for use in an insecticide emanator, said mat containing an insecticidal composition comprising one or more pyrethroid insecticide having a vapour pressure at 25°C of from 0.1 to 200 milliPascals (mPa) , preferably from 0.1 to 100 mPa, especially from 1 to 50 mPa, together with piperonyl butoxide and/or one or more analogues thereof, in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1. We have found that the use of piperonyl butoxide and/or its analogues, in the weight ratios specified above (which are very much less than those in which those compounds are conventionally used to synergise pyrethroid compositions) , surprisingly stabilises the pyrethroid insecticide to such an extent that a useful life of several days or months can be achieved. The term 'analogues' of piperonyl butoxide is used herein to include structurally similar compounds having substantially similar properties, especially analogues or homologues of 5-[ (2-(2-butoxyethoxy)ethoxy)methyl]-l,3- benzodioxole, for example 5-[ (2-(2-butoxyethoxy)ethoxy)- methyl]-l,3-benzodioxole, 5,6-di-[ (2-(2-butoxyethoxy)- ethoxy)methyl]-1,3-benzodioxole or 4 ,5,6-tri-[ (2-(2- butoxyethoxy)ethoxy)methyl]-l,3-benzodioxole. The pyrethroid insecticide is preferably allethrin, or bioallethrin, as individual stereoisomers or mixtures thereof, including in particular the (S)-cyclopentenyl isomer of bioallethrin, and d-allethrin (ie an 80:20 ratio of bioallethrin with the analogous esters of the (lR)-cis acid), which possess a vapour pressure in the defined range. When absorbed onto a mat in accordance with the invention, such insecticides can be vaporised into the atmosphere at a suitable rate, and without significant problems of stability, from an insecticide emanator at a temperature of from 90-120°C, ie significantly lower, and safer, than has been conventionally employed. Besides being of use in an insecticide emanator set to operate at temperatures of 90-120°C, the mats of the invention may also be used in conventional, higher temperature emanators particularly if the mat is spaced apart from the heating element. A non-absorbent spacer may conveniently be positioned between the heating element and the mat to provide a suitable temperature reduction at the mat's surface. Any such spacer is preferably such that it does not contact the whole of the mat surface, so as to allow insecticide vapour to escape from the mat. In another aspect, the invention provides a method of combating insects in which a surface of a mat containing an insecticide composition comprising one or more pyrethroid insecticide having a vapour pressure of from 0.1 to 200mPa at 25°C, together with piperonyl butoxide and/or one or more analogues thereof, in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1, is heated to a temperature effective to vaporise the insecticide into the atmosphere, eg from 90 to 120°C. In a further aspect, the invention provides novel insecticidal compositions which comprise one or more pyrethroid insecticide having a vapour pressure of from 0.1 to 200mPa at 25°C, together with piperonyl butoxide and/or one or more analogues thereof in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1. The weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues is preferably from 9:1 to 20:1. In addition to the stabilising effect of the piperonyl butoxide and/or analogues thereof, we have also found that it makes the rate of release of the insecticide from the mat more uniform, and in addition remains fluid in the mat so that, if only part of the mat is heated, the insecticide is able to migrate within the mat to the heated area, and become vaporised. This in turn enables a thick or oversize mat to be provided, containing a proportionately greater amount of insecticide, which increases still further the potential life of the mat. Where a thicker mat than usual is employed, it may be convenient to orientate the heating element vertically rather than horizontally, so as to reduce the possibility of condensation of insecticide vapour on the cooler parts of the mat. The mats of the invention may within reason contain any desired amount of the pyrethroid insecticide, generally reckoned on the basis of 5 to lOOmg, typically about 20mg, of insecticide for each 12 hours intended use. Since the mats are appropriate for use over an extended period, each preferably contains from 140mg to 7.2g of pyrethroid insecticide. If desired, the insecticide composition of the invention may contain further solvents, surfactants and adjuvants as required, and optionally a suitable dye to provide a colour change when the mat approaches exhaustion. Anthraquinone dyes have been found to be particularly useful in this respect. The invention is illustrated by the following examples, in which: Several mats of each of the types specified were prepared and aged on identical heaters with a 12 hours on, 12 hours off cycle, or a 10 hours on, 14 hours off cycle, as specified. Some of the mats were chemically analysed for the amount of pyrethroid insecticide remaining at various times of ageing. Others were tested for biological efficacy against mosquitoes. Average evolution rates of pyrethroid insecticide ( g/hr) were calculated by subtracting the amount of the insecticide remaining from the amount applied to the mat and dividing by the heating time. Biological efficacy tests were carried out in 2 m 3 glass sided chambers at a temperature of 27°C and 50% relative humidity. The mats were heated in an adjacent fume cabinet for a period of 1 hour prior to the tests to ensure they had reached a constant operating temperature. A batch of at least 50 mosquitoes (Aedes aeσypti) was released into the chamber. The heater and mat were then transferred to the centre of the floor of the chamber with power supplied continuously to the heater. The number of mosquitoes knocked down at l minute intervals up to 15 minutes was recorded. The times taken to knock down 50% of the population (KT50) and knock down 95% (KT95) were determined from these data. The temperature of the heater surface was measured using a calibrated thermocouple surface probe attached to a meter. Heat sink compound was used to ensure a good thermal contact between the heater surface and the probe. The average temperature was determined from a series of 8 readings across the heater surface in direct contact with the mat. In the examples: EBT is a 93% pure technical grade product supplied by Roussel Uclaf containing at least 72% of the (S)- cyclopentenyl isomer of bioallethrin and at least 21% m/m other allethrin isomers; SBA is a 95% pure technical grade product supplied by Roussel Uclaf containing at least 90% of the (S)- cyclopentenyl isomer of bioallethrin; Fat Blue B is an oil soluble anthraquinone dye supplied by Hoechst; Piperonyl butoxide (PB) is the technical grade material 91% pure supplied by Roussel Uclaf; Butylated hydroxy toluene (BHT) is Food Grade 99.5% pure material supplied by Nipa Laboratories; White Mineral Oil is Shell Ondina 15 supplied by Shell Chemicals; and Shellsol K is saturated hydrocarbon solvent with a boiling range 195° to 245°C supplied by Shell Chemicals. Example 1 Ingredient % w/w EBT 89.955 Piperonyl butoxide (PB) 9.995 Fat Blue B 0.050 (Ratio EBT:PB = 9:1) 770 mg of the above formulation (equivalent to 700 mg EBT) were applied to cardboard mats with dimensions 52 mm x 22 mm x 2.5 mm. Each mat was placed with the largest dimensions horizontally on the heater at a temperature of 105°C with an area 35 mm x 22 mm in contact with the heater surface. The volume of mat not directly heated remained covered with aluminium foil. Heating 12 hr EBT left Evolution KT50 KT90 Time hr eye :les (%) (mg/hr) (min) (min) 48 4 87 1.9 3.8 6.0 96 8 74 1.9 4.0 6.2 192 16 55 1.6 3.9 6.7 288 24 40 1.5 3.8 6.0 384 32 29 1.3 4.1 7.3 480 40 21 1.2 4.7 9.2 Example 2 Ingrediesnt % w /w EBT 83. 292 Piperonyl butoxide 16.658 Fat Blue B 0.050 (Ratio EBT:PB = 5:1) 840 mg of the above formulation (equivalent to 700 mg EBT) were applied to cardboard mats with dimensions of 70 mm x 22 mm x 2.5 mm. Each mat was placed with the largest dimensions horizontally on the heater at a temperature of 105°C with an area 35 mm x 22 mm in contact with the heater surface. The volume of mat not directly heated remained covered with aluminum foil. Heating 12 hr EBT left Evolution KT50 KT95 Time hr eye :les (%) (mg/hr) (min) (min) 48 4 92 1.2 6.1 9.8 96 8 83 1.2 6.1 9.4 192 16 69 1.1 6.3 9.3 288 24 56 1.1 6.8 10.0 384 32 47 1.0 6.4 10.0 480 40 39 1.9 6.0 9.1 Example 3 Ingredient w/w EBT 83.292 Piperonyl butoxide 16.658 Fat Blue B 0.050 (Ratio EBT:PB = 5:1) 840 mg of the above formulation (equivalent to 700 mg EBT) was applied to cardboard mats with dimensions of 70 mm x 22 mm x 2.5 mm. Each mat was placed with the largest dimensions horizontally on the heater at a temperature of 120°C with an area 35 mm x 22 mm in contact with the heater surface. The surface of the mat not directly heated remained covered with aluminium foil. Heating 12 hr EBT left Evolution KT50 KT95 Time hr cycles (%) (mg/hr) (min) (min) 48 4 76 3.8 3.1 5.2 96 8 57 3.1 3.2 5.4 192 16 32 2.4 4.1 6.8 288 24 18 2.0 6.2 11.0 384 32 10 1.6 8.0 >15.0 480 40 6 1.4 11.0 >15.0 Example 4 Ingredient %w/w EBT 83.292 Piperonyl butoxide 16.658 Fat Blue B 0.050 2500 mg of the above formulation (equivalent to 2083 mg EBT) was applied to cardboard mat. This was 2.5 mm thick and "T" shaped. The vertical stroke of the "T" was 22 mm wide and 35 mm long. The top stroke of the "T" was 35 wide and 66 mm long. Each mat was placed with the largest dimensions of the vertical stroke of the "T" horizontally on the heater at a temperature of 105°C with an area 34 mm x 22 mm in contact with he heater surface. The volume of mat not directly heated remained covered with aluminium foil. Heating 12 hr KT50 KT95 Time hr cycles (min) (min) 192 16 4.5 6.6 288 24 4.6 7.9 480 40 4.6 6.6 960 80 5.0 7.7 1440 120 5.4 7.7 1716 143 6.2 >15.0 Example 5 Ingredient %w/w S-Bioallethrin (SBA) 90.50 Piperonyl butoxide 9.05 Fat Blue ] B 0.45 3500 g of the above formulation (equivalent to 3167 mg SBA) was applied to a thick cardboard mat, ie a block, of dimensions 35mm x 22mm x 17.5mm. The block was placed with a 17.5 x 33mm side spaced 2mm apart from a vertical heater element at a temperature of 145°C, giving a surface temperature on the block of about 120°C. The other surfaces of the block remained covered with aluminium foil. Heating 10 hr KT50 KT95 Time hr cycles (min) (min) 10 1 3.8 8.2 300 30 4.1 10.5 400 40 3.0 11.5 1200 120 3.7 9.5 2000 200 4.4 12.1 Comparative Example 1 Ingredient % w/w EBT 21.5 Butylated hydroxy toluene 10.0 Fat Blue B 0.4 Shellsol K 20.0 White Mineral Oil 48.1 100 mg of the above formulation (equivalent to 21.5 mg EBT) were applied to standard cardboard mats with dimensions 35 mm x 22 mm x 2.5 mm. Each mat was placed with the largest dimensions horizontally on the heater at a temperature of 140°C with an area 35 mm x 22 mm in contact with the heater surface. The entire mat was placed on the heater. Heating EBT left Evol'n KT50 KT95 Time hr (%) (mg/hr) (min) (min) 0* 100 - 4.7 8.1 10 26 1.5 4.8 6.5 *Fresh mat placed on a heater at its operating temperature.

Claims: CLAIMS 1. A mat for use in an insecticide emanator, said mat containing an insecticidal composition comprising one or more pyrethroid insecticide having a vapour pressure of from 0.1 to 200 milliPascals (mPa) at 25°C, together with piperonyl butoxide and/or one or more analogues thereof, in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1. 2. A mat according to claim 1, in which the pyrethroid insecticide has a vapour pressure of from 0.1 to 100 mPa at 25°C. 3. A mat according to claim 2, in which the pyrethroid insecticide has a vapour pressure of from 1 to 50 mPa at 25°C. 4. A mat according to any of claims 1 to 3, in which the pyrethroid insecticide is allethrin or bioallethrin, including individual stereoiso ers or mixtures thereof. 5. A mat according to any of claims 1 to 4 which contains from 140mg to 7.2g of the pyrethroid insecticide. 6. A mat according to any of claims 1 to 5, in which the weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues is from 9:1 to 20:1. 7. A method of combating insects in which a surface of a mat containing an insecticidal composition comprising one or more pyrethroid insecticide having a vapour pressure of from 0.1 to 200mPa at 25°C, together with piperonyl butoxide and/or one or more analogues thereof in a weight ratio of insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1, is heated to a temperature effective to vaporise the insecticide into the atmosphere. 8. A method of combating insects according to claim 7, in which the mat surface is heated to a temperature of from 90 to 120°C. 9. An insecticidal composition which comprises one or more pyrethroid insecticide having a vapour pressure of from 0.1 to 200mPa at 25°C, together with piperonyl butoxide and/or one or more analogues thereof, in a weight ratio of pyrethroid insecticide to piperonyl butoxide and/or its analogues of from 5:1 to 50:1.

Inventors: MARTIN ROBERT, MARTIN, ROBERT
Applicants: AGREVO ENV HEALTH LTD, MARTIN ROBERT, AGREVO ENVIRONMENTAL HEALTH LIMITED, MARTIN, ROBERT
Application year: 1995
Main classification: A01N53
IPC codes: A01N25, A01N53