WO2004082376A1

WO2004082376A1 - Insect trapping device

Info

Publication number: WO2004082376A1
Application number: PCT/GB2004/001226
Authority: WO
Inventors: Frank Leighton
Original assignee: Texol Products Ltd
Priority date: 2003-03-21
Filing date: 2004-03-19
Publication date: 2004-09-30
Also published as: GB0306538D0; EP1605749A1; AU2004222505A1; NZ542745A

Abstract

The present invention provides an apparatus (10) for attraction and trapping insects, in particular blood sucking insects. The apparatus (10) includes a source of carbon dioxide (12) and a means (28) for exhausting the carbon dioxide into the surrounding atmosphere. The carbon dioxide is preferably produced within the apparatus from the combustion of a hydrocarbon gas. Further included in the apparatus of the invention are suction means (36) for the introduction of air and of insects into the apparatus (10), and retaining means for the retention of the introduced insects. The apparatus advantageously includes anti-dispersal means (38) which inhibits the dissipation of the carbon dioxide into an area distant from the apparatus.

Description

"Insect Trapping Device"

The present invention relates to a device for attracting and/or trapping insects. More specifically, the invention provides a device for attracting, capturing and killing haematophagous flying insects .

Background to the Invention Bloodsucking (haematophagous) flying insects are commonly attracted to a potential living blood source such as a human through the detection of a mixture of carbon dioxide, air and water vapour present in exhaled breath. Thus the insects are attracted towards a specific concentration of gases released at a specific temperature.

Insects are also known to be attracted to traps by the use of lights or attractants such as sugar-based solutions or chemical attractants. Once in the vicinity of the trap various means are commonly used to contain or kill the insects. Such means include drowning or use of insecticides. Further insect traps, such as those typically designed for the trapping of mosquitoes, are also known in the field. In these traps carbon dioxide gas and/or chemical attractants such as octenol are released into the vicinity of the trap. This carbon dioxide and attractant mixture attracts insects along aconcentration gradient towards the trap. Once in the vicinity of the trap a suction mechanism is used to draw the mosquitoes into the trap, where they are retained until they die or are disposed of.

International PCT Patent Publication No W099/37145 describes one such device. Hydrocarbon gas fuel is burnt to produce a gaseous mixture of carbon dioxide and water vapour. The gases are then released downwardly. Insects attracted towards the device are drawn into the device by suction and are thus trapped.

However, the release of the carbon dioxide and attractant from such prior art traps causes their rapid dissipation into the surrounding atmosphere, particularly in exposed or windy conditions. The dissipation of the attractants into the atmosphere results in their becoming too diluted to provide an effective concentration gradient which can attract the mosquitoes towards the trap. As such, they become ineffective for insect attraction.

A further disadvantage to the presence of peripheral air currents is the dissipation of heat from the carbon dioxide and attractant mixture. Mosquitoes are commonly attracted to heated gaseous mixtures and thus where the gas emitted is not maintained at optimal temperature, the efficiency of insect capture is much reduced.

The generation of carbon dioxide and attractant such that it is expelled about the periphery of a trap is an important step in the function of insect traps. However, the dissipation of the attractant- containing gases results in the traps losing trapping efficiency and also being less energy efficient as more carbon dioxide needs to be produced to provide an emission level which can be detected by insects.

Summary of the Invention According to a first aspect of the present invention, there is provided an insect trapping apparatus including: a source of carbon dioxide; an exhaust means from which the carbon dioxide is exhausted; a suction means for drawing air into the apparatus and being adequate to allow the ingress of insects contained within the air, the insects being drawn into the apparatus at an area proximal to where the gas is exhausted from the apparatus; means for retaining the insects which are drawn into the apparatus; and at least one anti-dispersal means for reducing dissipation of gas exhausted from the apparatus. Preferably the exhaust means is adapted to direct the exhausted carbon dioxide substantially towards the anti-dispersal means.

Preferably the exhaust means includes an exit port through which the carbon dioxide is exhausted.

Anti-Dispersal Means Preferably the anti-dispersal means is positioned in spaced arrangement with the exit port. More preferably the anti-dispersal means is located above the exit port. More preferably still the anti- dispersal means is concentric with the exit port. For example, in a preferred embodiment the centre of the anti-dispersal means may be located several centimetres above the centre of the exit port such that the anti-dispersal means provides equal cover on all sides of the exit port.

The anti-dispersal means can be composed, of at least one carbon dioxide retaining plate member extending around the exit port and thus defining a carbon dioxide retaining area. The carbon dioxide retaining area is preferably located around the exhaust means, more preferably around the exit port.

The anti-dispersal means serves to shelter the plume of exhausted gases from peripheral air currents and their cooling effect, thus preventing the dissipation of the attractant gases into the atmosphere. The exhausted attractant mixture is therefore concentrated around the device, generally in the region of the carbon dioxide retaining area. The concentration gradient that the insect follows is thus increased and insects are more effectively ^' attracted to the device where they can be trapped.

The at least one carbon dioxide retaining plate member may be any shape suitable to define the carbon dioxide retaining area . The member may typically be planar, arcuate or a combination of both.

In a preferred embodiment, the anti-dispersal means is of a generally inverted dish shape i.e. is concave towards the exit port . Thus the carbon dioxide retaining plate member may curve downwardly towards the exit port at its peripheral edge(s) .

Preferably the at least one carbon dioxide retaining member is a series of flanges projecting outwardly from the apparatus. Each flange preferably extends outwardly from a side of a central planar hexagonal plate at an angle such that a carbon dioxide retaining area is defined around the exit port through which the gases are exhausted.

The hexagonal plate may be positioned in any position suitable for retaining carbon dioxide in the vicinity of the exit port. For example, the hexagonal plate may preferably be positioned above the exit port. A further advantage of the anti-dispersal means is that it prevents the escape of attracted insects such that they are more easily trapped.

The anti-dispersal means also serves as a weather cover. Precipitation is thus prevented from entering the system and the carbon dioxide exhausted is kept within the local vicinity of the device.

Carbon Dioxide Source The carbon dioxide source may be any suitable source of carbon dioxide. For example, the carbon dioxide source may be a pressurised canister of carbon dioxide. Alternatively, the carbon dioxide can evaporate from a source of dry ice. Preferably the carbon dioxide is produced by the combustion of a mixture of gas and air, most preferably in the presence of a catalyst.

Preferably the gas is a hydrocarbon gas such as propane, butane or a suitable mixture thereof. Alternatively, the gas is Patio Gas™, a propane/butane mixture supplied by Calor UK.

The gas is preferably stored within a container and discharged via a 37mb pressure regulator. The gas container is preferably stored within the device in a self-contained housing. The gas preferably enters the combustion chamber through a nozzle which controls gas flow and pressure. The skilled reader will be aware that the regulated pressure of gas supplied from containers may vary in different countries and therefore modifications to the nozzle may be required to obtain effective functioning of the apparatus. Such modifications will be obvious to the skilled man. For example, with a regulated pressure of 37mb, a nozzle size of 0.3mm is suitable to allow sufficient gas to feed into the combustion chamber for a power requirement of 0.25k .

Typically, the nozzle housing has at least one hole to permit the flow of gas to draw the required amount of air into the system to allow complete combustion. Complete combustion means that no hydrocarbons are included in the gas which is exhausted from the apparatus.

Preferably the carbon dioxide is mixed with air prior to being exhausted from the apparatus. The apparatus preferably further includes a second suction means for drawing air into the apparatus.

The air to be mixed with the carbon dioxide is typically drawn into the device via the second suction means. Typically when the carbon dioxide is produced from the combustion of a mixture of gas and air, the carbon dioxide is exhausted as a mixture of carbon dioxide, air and water vapour. Combustion typically takes place within a combustion chamber, which is preferably manufactured from cast aluminium. Preferably the second suction means, for the suction of air, is provided by a venturi arrangement. For the purposes of the present invention a venturi arrangement is defined as an opening which narrows, causing a build-up of pressure sufficient to draw air into the apparatus of the invention.

Catalyst The catalyst is preferably one which allows the combustion of gas and air without a flame and which, when operating at full working temperature, results in the release of carbon dioxide. The catalyst is preferably in the form of a monolith block.

Preferably the catalyst is a substrate coated with at least 200m²/g platinum. The greater the surface area of the catalyst, the better the performance of the catalyst at comparable precious metal content.

Pelleted catalysts have a lower surface area (< lOOmVg) than coated substrates (>200m²/g) as the pellets are packed together reducing the available surface area. Coated substrates such as that of the present invention have a greater resistance to higher temperatures and against contaminants. They also contain oxygen storage compounds making the combustion process easier to initiate than beaded catalysts. For example, ignition within the present apparatus typically requires only one spark. The catalyst has the advantage that it has better resistance against high temperatures . The catalyst typically burns in the region of 500°C to 1500°C. The ability to withstand high combustion temperatures means that contaminants such as carbon monoxide are not produced so that carbon deposits from the hydrocarbon gas source do not build up on and detrimentally affect the functioning of the catalyst .

A wide range of catalysts are known in the art and a suitable catalyst will be known to the skilled man.

The catalyst is typically housed in a chamber.

Carbon Dioxide Exhaust Preferably the carbon dioxide concentration immediately following combustion is between 6000 to 12000 ppm at a temperature which is preferably in the region of between 160°C to 210°C. More preferably the carbon dioxide is exhausted at a concentration of between 8000 to 10000 ppm carbon dioxide at a temperature of 190°C.

In one embodiment of the present invention, the carbon dioxide mixture is exhausted from the apparatus at a concentration of between 500 to 10000 ppm, more preferably between 600 to 7000. Most preferably the carbon dioxide mixture is exhausted at a concentration of approximately 4600 ppm. The temperature of the carbon dioxide mixture on exhaustion from the apparatus may be at a temperature of between 22 and 45 °C, preferably between 24 and 42°C. Most preferably the temperature of the carbon dioxide mixture is maintained at between 10 to 15 °C above ambient temperature (i.e. above the temperature of the surrounding atmosphere) .

Preferably the carbon dioxide mixture is exhausted from an exhaust pipe, or similar outlet means, through the exit port .

Preferably the outward flow of the exhausted carbon dioxide is effected by at least one fan. The fan may suitably be a 40mm fan.

The exterior end of the exhaust pipe may be oriented in any direction suitable for the attraction of insects. Preferably the exterior end of the exhaust pipe is oriented in an upwards direction. The gaseous attractant mixture is therefore preferably exhausted upwardly.

An output of approximately 4600 parts per million (ppm) carbon dioxide at a temperature 10 - 20 °C above ambient temperature is preferred. An output velocity of between 3 to 3.5 km/h or 1.5 to 2 mph is also preferred. This level of output ensures that the denser carbon dioxide does not sink immediately upon exhaustion. Preferably an insect attractant is added to the carbon dioxide prior to it being exhausted. Alternatively, a cartridge containing the insect attractant is located near to the exterior exit port of the exhaust means .

Preferably the attractant is an insect sex attractant pheromone . More preferably the attractant is octenol (l-octen-3-ol) . Alternatively, the attractant is octanol, octonal, 1-heptanol, 3 -octanol or the like.

Insect Trapping Preferably the first suctio means is provided by at least one fan, more preferably two fans. The at least one fan may suitably be a 92mm fan. A suction rate of 4.5 to 5.5 km/h or 2 to 3.5 mph is preferred.

The at least one fan. is preferably driven by thermoelectric generation. Preferably at least two thermoelectric generators are connected in series and are further connected in series to the at least one fan, forming an electrical circuit. More preferably four thermoelectric generators are used.

Thermoelectric generators suitable for use with the invention will be known to the skilled man. Suitable thermoelectric generators can be obtained from suppliers such as elcor, FerroTec and Supercool AB. Such thermoelectric generators can be manufactured to the specification required for use with the apparatus. A single thermoelectric generator assembly can be used to power the apparatus at 12 volts and 0.5 amps. Preferably four thermoelectric generators connected in series are used.

The exterior end of the first suction means can be oriented in any direction suitable for the drawing in of insects. Preferably the exterior end of the first suction means is oriented in an upwards direction. Insects are preferably drawn into the apparatus through a suction pipe.

The exterior ends of both the suction and exhaust pipes are most preferably oriented in an upwards direction.

Further, the entrance port of the suction pipe and the exit port of the exhaust pipe are preferably located proximal to each other.

The portion of the suction pipe that extends exterior to the apparatus preferably envelops the exterior portion of the exhaust pipe. This portion of the suction pipe may optionally take the form of a funnel shape where it envelops the exhaust pipe.

The interior end of the suction pipe is preferably enclosed in the retaining means.

Preferably the retaining means is a capture bag or the like. The capture bag is preferably disposable. A further advantage of the present apparatus is that heat from the gas combustion is retained within the apparatus such that trapped insects are killed and become desiccated. The temperature in the vicinity of the insect retaining means is generally 10°C above ambient temperature when the apparatus is in operation. Killed and desiccated insects can thus be removed easily and hygienically from the apparatus, eliminating the possibility that the insects may escape and/or inflict further bites.

The insects trapped by the apparatus are any haematophagous insects . According to one embodiment of the invention, the insects are from the family Ceratopogonidae, preferably midges. According to an alternative embodiment of the invention, the insects are mosquitoes.

Additional Features Preferably the trapping apparatus can further include a safety mechanism which maintains a safe operating temperature.

The safety mechanism preferably includes a safety valve, a safety valve button, a thermocouple and a bimetallic switch. The safety valve, safety valve button, thermocouple and bimetallic switch are preferably connected in a circuit.

The safety valve controls the flow of gas into the combustion chamber. The thermocouple is preferably located such that it detects the temperature of the combustion chamber and the temperature of the chamber housing the catalyst . When the temperature differential between the two chambers is sufficiently high, a voltage flows along the thermocouple to maintain the safety valve in its open position. If the temperature in the combustion chamber drops or the catalyst malfunctions, the valve closes, thus preventing gas entering the combustion chamber.

The bimetallic switch is preferably located on the outer wall of the combustion chamber and is connected in circuit with the safety valve such that if the trapping apparatus overheats the safety valve closes. The trapping apparatus is deemed to have overheated when the temperature of the outer wall of the combustion chamber exceeds 120°C.

The apparatus may further include a multispark igniter. This is an electronic battery operated device. On depression it provides a continuous spark to the combustion chamber so as to ignite the gas/air fuel mixture.

The apparatus may also include a voltmeter or other voltage indicator to provide a visual reading of the power generated by the thermoelectric generators. For example, a red colour on a power indicator may show that the apparatus is warming up whilst a green colour could indicate that the apparatus is fully operational. At least one exhaust vent may be provided in the walls of the combustion chamber so as to allow for free movement of the air drawn in by the fans. This aids the suction of air and facilitates maintenance of a continuous air speed, for example approximately 11 km/h. Such an air speed helps prevent the entrance of insects into the combustion mechanism.

The apparatus may also be used merely for attracting insects.

According to a second aspect of the present invention, there is provided an insect trapping apparatus including: a source of carbon dioxide; an exhaust means from which the carbon dioxide is exhausted in an upward direction; a suction means for drawing air into the apparatus and being adequate to allow the ingress of insects contained within the air, the insects being drawn into the apparatus at an area proximal to the area from which gas is exhausted; means for retaining the insects which are drawn into the apparatus; and a top shield for reducing dissipation of gas exhausted from the apparatus, wherein the top shield is positioned in spaced relationship above the exhaust means. Preferred features of each aspect of the invention are as for each other aspect, mutatis mutandis unless the context demands otherwise.

Figures An embodiment of the invention will now be described, by way of example only, with reference to the following drawings which are not intended to be construed as being limiting on the present invention, wherein: Figure 1 shows a side view of the upper part of the trapping apparatus; Figure 2 shows a perspective top view of the trapping apparatus ,- Figure 3 shows a front view of the combustion chamber and heat sink of the trapping apparatus; Figure 4 shows a cross section of the front view of the combustion chamber and heat sink along line A-A in the direction shown in Figure 3; Figure 5 shows a schematic of the upper part of the apparatus of the invention (A) and a table of measurements (B) of carbon dioxide concentrations and temperatures taken at six specific areas shown on the schematic; and Figure 6 shows a schematic (A) of the combustion chamber and the exhaust and suction pipes, with an enlarged view (B) of the components of the combustion chamber.

The trapping apparatus 10 has a combustion chamber 12 housing a chamber 14 which contains a catalyst 54. A thermocouple 16 is located inside the combustion chamber 12 and is in contact with the catalyst chamber 1 . A spark igniter 18 is also located inside the combustion chamber 12. The base of the combustion chamber 12 is mounted on a venturi arrangement housed within a nozzle housing 20. A jet carrier 24 is located at the base of the nozzle housing 20. A gas nozzle 22 is also provided at the base of the combustion chamber 12. A sintered disc (not shown) is located between the gas nozzle 22 and the combustion chamber 12.

An exhaust chimney 26 houses an inner exhaust pipe 28. The thermoelectric generators 30 are arranged between the outer wall of the combustion chamber 12 and a heat sink 32. A heat plate 56 is used in conjunction with heat transfer pins 58 to assist in thermal conductivity of the heat generated from combustion to the hot side 48 of the thermoelectric generators 30. The heat pins 58 are provided above and below the catalyst 54 to ensure effective heat transfer through to the heat plate 56 and thus to the thermoelectric generators 30. The high thermal conductivity of the cast aluminium combustion chamber 12 further assists in heat transfer to the thermoelectric generators 30.

The heat plate 56 is generally made of aluminium but may be made from copper. It is generally approximately 3mm thick.

The combustion chamber 12, thermoelectric generators 30 and heat sink 32 are housed in a first outer housing 34. A capture chamber (not shown) is located inside the first outer housing 34. An outer suction pipe 36 extends from the top of the first outer housing 34 into the capture chamber and envelops the exhaust chimney 26. The portion of the suction pipe 36 which extends exterior to the apparatus 10 forms a funnel shape 36A. A vapour shield (anti-dispersal means/top shield) 38 is mounted above the inner exhaust pipe 28.

A door 40 leading to the capture chamber is provided on the first outer housing 34. A service panel 42 is also provided on the first outer housing 34. A multi-spark ignition switch 44 is situated on the service panel 42. An air vent 66 is also located in the first outer housing 34. The first outer housing 34 is mounted on a second outer housing 46, which houses a gas cylinder (not shown) .

The trapping apparatus 10 as shown in Figures 1 and 2 is mounted on wheels 50.

In use, a gas cylinder (not shown) is housed within the second outer housing 46. A safety valve button 60 is activated to draw gas from the gas cylinder through the nozzle 22 and sintered disc into the combustion chamber 12. The venturi arrangement simultaneously draws air into the combustion chamber 12. The ignition switch 44 is depressed, activating the spark igniter 18 and causing the gas and air mixture to ignite. A temperature differential thus builds up between the combustion chamber 12 and the heat sink 32. The gas mixture burns until the oxygen in the air is used up and the catalyst 54 reaches its working temperature of 350 °C (measured on the top surface of the active catalyst; the temperature of the inside of the catalyst can reach up to 800°C) . The gas is now burnt completely by catalytic conversion producing steam and 8000 - 10000 ppm carbon dioxide at 190 °C (i.e. at the exhaust chimney 26, directly above the combustion chamber 12) . A power indicator 68 indicates that the apparatus has reached this stage.

When the temperature differential between the combustion chamber 12 and the catalyst chamber 14 is sufficiently high, the thermocouple 16 produces a voltage which holds the safety valve open. The temperature differential is sufficient when a voltage of 5 millivolts is generated. The safety valve button 60 may then be deactivated.

The heat from the operational catalyst 54 is transferred via the heat pins 58 and plates 56 through the walls of the combustion chamber 12 to the thermo-electric generators 30, which are connected to an electrical output and which convert the temperature differential between the combustion chamber 12 and the heat sink 32 into a voltage which is used to drive the inlet and outlet fans 62,64. The voltage required to activate the fans is approximately 3 volts. The inlet fan 62 helps maintain the temperature differential between the combustion chamber 12 and the heat sink 32. The outlet fan 64 mixes the carbon dioxide produced from combustion and the air drawn in through the second suction means, and forces the mixture up the inner exhaust pipe 28 and out through the exhaust chimney 26. The carbon dioxide/water vapour/air mixture leaves the exhaust chimney 26 at a concentration of 800 to 5000 ppm carbon dioxide and at a temperature in the region of 10 to 15 °C above ambient temperature, ambient temperature being between 15 to 25 °C, for example 20 to 22 °C.

A cartridge 52 containing an insect attractant, such as octenol, is placed at the exit of the inner exhaust pipe 28. When octenol evaporates from the cartridge 52, it mixes with the carbon dioxide/water vapour/air mixture, forming an insect-attracting vapour.

The warmth of the carbon dioxide mixture causes the gaseous mixture to rise up from the exit port of the exhaust pipe 28. As described supra, such plumes of attractant are vulnerable to dissipation caused by air currents such that insects are not optimally attracted.

However, the vapour shield 38 of the present invention inhibits the attractant vapour from dissipating from the local vicinity of the trapping apparatus 10. The downwardly curved peripheral edges and the location of the vapour shield 38 above the exit port help protect the carbon dioxide attractant mixture from surrounding air currents. The concentration and temperature of the carbon dioxide mixture are thus reliably maintained at known and relatively constant levels, and insect trapping is optimised.

The attracted insects are drawn in by the inlet fan 62 through the outer suction pipe 36 into the capture bag (not shown) . Once the capture bag is sufficiently full, the bag may be detached from the interior end of the suction pipe 36, sealed and disposed of. The capture bag is generally sufficiently full when it is half to three quarters full of insects.

Figure 5 shows the results of a test conducted to determine the efficacy of the vapour shield 38 and apparatus design in retaining the mixture of carbon dioxide, water vapour and air in the local vicinity of the suction means. Measurements of temperature and carbon dioxide concentration were taken. The ambient carbon dioxide concentration was measured as 600 parts per million (ppm) , and the ambient temperature as 22 °C. Measurement 1 was taken 100mm above the attractant container 52.

The output velocity from the exhaust pipe 28 was measured at point (i) in Figure 5 as 1.9 miles per hour (mph) (3.2 kilometres per hour (km/h)), and the suction velocity of the suction pipe 36 was measured at point (ii) in Figure 5 as 3.3 mph (4.8 km/h) . As can be seen from the results shown in the table in B of Figure 5, the vapour shield 38 was effective at retaining advantageous carbon dioxide concentrations and temperatures in the local vicinity of the suction pipe 36. These carbon dioxide concentrations and temperatures are thought to be optimal for insect attraction and thus the efficiency of the apparatus is improved.

It will be understood by one skilled in the art that various modifications and variations may be made to the invention as herein described without departing from the scope of the invention. Although the invention has been described in connection with specific examples, it should be understood that the invention as claimed should not be unduly limited to such examples. For example, the chemical attractant may be replaced by any chemical attractant commonly known in the field. The capture bags may optionally contain an insecticide.

Claims

1. An insect trapping apparatus including: a source of carbon dioxide; an exhaust means from which the carbon dioxide is exhausted; a suction means for drawing air into the apparatus and being adequate to allow the ingress of insects contained within the air, the insects being drawn into the apparatus at an area proximal to where the gas is exhausted from the apparatus ; means for retaining insects which are drawn into the apparatus ; and at least one anti -dispersal means for reducing dissipation of gas exhausted from the apparatus.

2. An apparatus as claimed in claim 1 wherein the exhaust means is adapted to direct the exhausted carbon dioxide towards the anti- dispersal means.

3. An apparatus as claimed in claim 1 or claim 2 wherein the exhaust means includes an exit port through which the carbon dioxide is exhausted.

4. An apparatus as claimed in claim 1 to claim 3 wherein the anti-dispersal means is in spaced arrangement with the exit port.

5. An apparatus as claimed in any of claims 1 to 4 wherein the anti-dispersal means is located above the exit port .

6. An apparatus as claimed claim 4 or 5 wherein the anti-dispersal means is concentric with the exit port .

7. An apparatus as claimed in any preceding claim wherein the anti-dispersal means is concave towards the exit port.

8. An apparatus as claimed in any preceding claim wherein the anti-dispersal means is composed of at least one carbon dioxide retaining member extending around the exit port and thus defining a carbon dioxide retaining area.

9. An apparatus as claimed in claim 8 wherein the carbon dioxide retaining member is a series of flanges projecting outwardly from the apparatus.

10. An apparatus as claimed in claim 9 wherein each flange projects outwardly from a side of a planar hexagonal plate at an angle such that the carbon dioxide retaining area is defined around the exit port.

11. An apparatus as claimed in any preceding claim wherein the source of carbon dioxide is combustion of a mixture of gas and air.

12. An apparatus as claimed in claim 11 wherein the combustion takes place in the presence of a catalyst .

13. An apparatus as claimed in claim 12 wherein the catalyst is a platinum-coated monolith block.

14. An apparatus as claimed in any of claims 11 to 13 wherein the gas is propane, butane or a suitable mixture thereof .

15. An apparatus as claimed in any preceding claim wherein the carbon dioxide is mixed with air prior to being exhausted through the exit port.

16. An apparatus as claimed in claim 15 wherein the air which is mixed with the carbon dioxide is drawn in by a further suction means.

17. An apparatus as claimed in any preceding claim wherein the carbon dioxide is exhausted as a mixture of carbon dioxide, air and water vapour .

18. An apparatus as claimed in any preceding claim wherein an insect attractant is added to the carbon dioxide prior to its exhaustion.

19. An apparatus as claimed in any preceding claim wherein the carbon dioxide is exhausted at a concentration of between 500 to 10000 ppm.

20. An apparatus as claimed in claims 1 to 18 wherein the carbon dioxide is exhausted at approximately 4600 ppm.

21. An apparatus as claimed in any preceding claim wherein the carbon dioxide is exhausted at between 22 °C to 45 °C.

22. An apparatus as claimed in claims 1 to 20 wherein the carbon dioxide is exhausted at between 24 °C to 42 °C.

23. An apparatus as claimed in any preceding claim wherein the carbon dioxide is exhausted at a velocity of between 3 to 3.5 km/h.

24. An apparatus as claimed in any preceding claim wherein the carbon dioxide is exhausted from an exhaust pipe.

25. An apparatus as claimed in claim 24 wherein the exterior end of the exhaust pipe is oriented in an upward direction.

26. An apparatus as claimed in claim 24 wherein the exterior end of the exhaust pipe is adapted to be directed towards the anti-dispersal means.

27. An apparatus as claimed in any preceding claim wherein the suction means includes at least one fan and a suction pipe.

28. An apparatus as claimed in claim 27 wherein the exterior portion of the suction pipe is located proximal to the area where gas is exhausted from the exhaust means .

29. An apparatus as claimed in claim 27 or 28 wherein the portion of the suction pipe exterior to the apparatus envelops the exterior portion of the exit port through which carbon dioxide is exhausted.

30. An apparatus as claimed in claim 29 wherein the exterior enveloping portion of the suction pipe is substantially funnel-shaped.

31. An apparatus as claimed in any one of claims 27 to 30 wherein the interior end of the suction pipe is connected to the retaining means.

32. An apparatus as claimed in any preceding claim wherein the suction rate of the suction means is between 4.5 to 5.5 km/h.

33. An apparatus as claimed in any preceding claim wherein at least one air vent is provided in the walls of the apparatus.

34. An insect trapping device including: a source of carbon dioxide; an exhaust means from which the carbon dioxide is exhausted in an upward direction; a suction means for drawing air into the apparatus and being adequate to allow the ingress of insects contained within the air, the insects being drawn into the apparatus at an area proximal to the area from which gas is exhausted; means for retaining insects drawn into the apparatus ; and a top shield for reducing dissipation of gas exhausted from the apparatus, wherein the top shield is positioned in spaced relationship above the exhaust means .