PROCEDURE FOR SETTING OUT EVSTYPE DRY ICE (CARBON DIOXIDE)

If, after checking the wiring, the light works but the fan does not, try gently pushing the central portion of the fan blades upward towards the motor. With the unit switched on but the fan still not working, try gently turning the blades in the right direction to see if movement starts. If it does work check if the down draft is strong enough, and also tilt the motor sideways and upside down to see if it continues working. Switch on and off several times and leave running for about 30 minutes. If the motor runs for this period of time then trapping should continue (See also trap maintenance section).

4. TRAP MODIFICATIONS DUE TO WET WEATHER.

If the trap is operated in wet weather, it should have a plastic skirt suspended from the base of the motor unit, and all the way down and around the catch container to exclude rain. The skirt should be sealed at the bottom by an elastic band so that mosquitoes are not trapped between the plastic and the container. A broad rain hood positioned over the top of the dry ice bucket would also be effective in keeping the trap and catch dry.

5(a). DRY ICE.

When using dry ice it should be collected from the manufacturer in the late afternoon of the trapping night. If a field trip for a number of nights is planned, the dry ice should be stored in a well insulated esky sealed with tape. As a rough guide approximately half the weight of the dry ice will disappear in the esky every two days, and a half a kilogram is needed per trap per night. The dry ice is placed in the trap bucket just before the trap is set out in the evening.

5(b). DRY ICE ALTERNATIVES.

There are problems associated with obtaining a regular supply of dry ice in some areas and two alternative systems are available.

It is possible to make blocks of dry ice directly from a gas cylinder. This method can be difficult to maintain and a lot of CO₂ gas can be wasted initially trying to produce a block of dry ice of the right size and density necessary to last out a night of trapping.

Alternatively the dry-ice can be replaced by carbon dioxide gas from a 10 kg cylinder with a slow release valve, set to release the gas at a rate of 300ml per minute (range 200 ‑ 400ml/min). Pressure on the delivery side of the main regulator needs to be set between 140 ‑ 160 kpa. If less than 140 kpa, then often the gas does not flow through properly, particularly towards the end of the season when gas pressure in the cylinder is getting low. If used once a week, a 10 kg cylinder running from 4 pm until 9 am the next day, should last about 20 weeks. The approximate flow rate can be checked by filling a 250ml sampling bottle with water, inverting the bottle in water without emptying the bottle, and releasing gas into the bottle for about 50 seconds. By then the gas should have more or less displaced all the water in the bottle.

6. SITE SELECTION.

Select the trap site with care, keeping in mind the purpose of the trap. Usually the trap should be positioned between a residential area and the mosquito breeding area, or at the edge of a mosquito breeding area. The site should be near vegetation, out of strong winds, away from competing lights, and away from congregations of animals. The trap should be hung at approximately chest height from a tree or similar object.

7. SETTING THE TRAP.

Install the batteries and check to ensure that the polarity is the same, and that the fan is blowing air in the right direction. The CO₂ exit holes in the bottom of the bucket should be checked for blockages by pushing the lid of the container in and out, noting whether CO₂ vapour is visibly flowing out the holes. If it is not, then open the holes with a thin wire or strong twig.

8. LABELLING TRAP.

Number or label the traps and collection/catch containers in some way so as to not mix up traps from different sites, and place the trap out about 1 ‑ 2 hours before sunset. Make sure no branches or leaves are touching the trap. Double check that no ants are in the tree and, if necessary, coat approximately 10 cm of the chain with petroleum jelly for protection.

It is very important that traps be set at the same sites each week, and ideally for a number of years, to obtain meaningful comparative population data. Moving the trap to different sites means that collections cannot be compared between trapping nights at weekly, monthly or yearly intervals.

9. RECOMMENDED TRAPPING NIGHTS.

Traps are best set out on Sunday, Monday, Tuesday, or Wednesday nights. Do not trap after Wednesday night as any delay in the courier service will result in the specimens arriving too late for processing. Preferably traps should be set as early as possible in the week so that if there is bad weather trapping can still be carried out by Wednesday.

10(a). COLLECTING THE TRAP.

Collect the trap the following morning within 2 hours of sunrise, and preferably earlier during hot sunny weather. This is to prevent the mosquitoes dying from heat stress or dehydration. While mosquitoes should be sent in alive ‑ as live mosquitoes are needed for virus isolation - dead mosquitoes are sorted into species to at least obtain continuous trapping data for each site.

10(b). CAUTION.

Before removing the catch container and switching off the motor, inspect the trap catch container for mosquitoes. Note that if the mosquitoes are capable of flying up into the sleeve or into the PVC tubing, then the fan is not operating fast enough.

11. INSPECT TRAP FAN AND LIGHT OPERATION.

The trap light and fan should still be running in the morning. If not, or if the fan is running too slowly, then label the trap for servicing or repair (see Point 3).

12. IF TRAP FAILURE OCCURS.

If a trap's motor or batteries have failed during the night, then another trap should be run at the site the following night.

13. REMOVING MOSQUITO COLLECTION CONTAINER.

Leave the mosquitoes in the collection containers with the lid still on. To remove the catch container choke off the top of the sleeve with one hand and remove the top of the sleeve from the PVC tube. Tie off and seal the top of the sleeve to prevent mosquitoes escaping. Check the label on the container is correct and that the lid on the catch container is not likely to come off (tape on if necessary).

14. TRAP MAINTENANCE.