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Northern Territory Department of Health Library Services Historical Collection
, DL HIST
614.4323WHE
1989
MOSQUITO CONTROL SITUATION - ALICE SPRINGS
APRIL 1989
NT DEPARTMENT OF HEALTH AND COMMUNITY SERVICES
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CENTRAL LIBRARY
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TERRITORY H!AL TH SERVICES
MOSQUITO CONTROL SITUATION - ALICE SPRINGS
APRIL 1989
Peter Whelan
Senior Medical Entomologist
DEPARTMENT OF HEALTH AND COMMUNITY SERVICES
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MOSQUITO CONTROL SITUATION - ALICE SPRINGS - APRIL 1989
1. 0 INTRODUCTION
Two officers from the Medical Entomology Branch visited Alice Springs from the 5th to the 7th April 1989 to liaise with the Alice Springs Council and the Regional Health Surveyors on current mosquito monitoring and control operations following the heavy rains the previous week.
2. 0 LARVAL SURVEY OF IL PARPA SWAMP
During the visit, an inspection and larval survey was carried out over Il Parpa Swamp to assess the impact of previous recommendations to reduce mosquito breeding.
The pipeline conveying excess sewage effluent from the old sewage ponds to the lower reaches of Il Parpa Swamp has now been installed by the Power and Water Authority. This measure was recommended to Power and Water Authority consultants as a means of reducing the area of mosquito breeding. An inspection on the 6th April revealed that the excess effluent from the old ponds is now confined to a much more defined area in the lower reaches of the swamp.
This area of effluent is composed of a relatively high proportion of open water with a bare mud substrate, amid clumps of Lignum and Typha vegetation. There were some areas of flooded grass closer to the pipe outlet and around various areas of the margin. The water depth is up to 400 millimetres deep and was relatively cool during the time of the survey.
Mosquito breeding was confined to the dense flooded grass areas, with no larvae being present in the dense Typha patches, in the Lignum patches or in the open water.
There were relatively high numbers of aquatic bugs and aquatic beetle larvae in the water. These aquatic predators are playing a significant role in the biological control of mosquito larvae in this swamp. Both Culex annulirostris and Anopheles annulipes larvae were present, with Cx. annulirostris present in low to moderate numbers in restricted areas of flooded grass.
The water from the outlet of the excess sewage line was relatively turbid and green at the outlet point. Organic matter and turbidity reduced fairly rapidly away from the pipe outlet as the water was distributed, f i r s t through the grass, and then into the open water. The outlet pipe had a T-section with a valve approximately 100 metres before the end of the straight line outlet. Water was being discharged from both the valve outlet and from the straight line outlet which was at the lower point of the swamp. The reason for this mechanism is unknown, and has the result of contributing to a larger flooded area than appears to be necessary. If there are no engineering reasons for this double outlet, i t is recommended that the shorter valve
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controlled outlet be discontinued, and all the water be discharged via the pipe outlet in the lower portion of the swamp.
There is no discharge of excess effluent from the new sewage ponds further west. A very large area of the formerly flooded Typha reed area of the swamp was dry, and this was in spite of recent rains.
I t is fairly obvious that the recommended pipeline has deprived a very large area of Il Parpa Swam~ of water and much of the area of Typha reeds is actually dying. This pipeline appears to have dramatically reduced the available area of mosquito breeding and has undoubtedly reduced the overall numbers of mosquitoes arising from the swamp. At the time of the visit, mosquito numbers as assessed by the regular joint Alice Springs Council - Department of Health and Community Services mosquito monitoring program were very low.
3. 0 SURVEY OF THE SEWAGE PONDS
The old sewage ponds were free of mosquito breeding, despite some marginal vegetation. There were very many aquatic insects in the secondary ponds, and there was considerable wave action that further discouraged mosquito breeding. The primary ponds have recently been cleaned out, and this is a dramatic improvement since the last survey. There are some Typha reeds beginning to grow at the edges of the primary ponds, and i t is suggested that these should be treated with weedicide as soon as possible to completely eliminate them.
There was a small discharge from the old valve controlled pipeline on the previous discharge pipe. While not resulting in any mosquito breeding, this valve and pipeline should be removed or completely sealed so that no further discharges are possible from this point.
4. 0 DISCUSSIONS WITH THE REGIONAL HEALTH SURVEYOR
The recent mosquito monitoring data and vector control operations were discussed with Mr Harold Brown, the Regional Health Surveyor for the Department of Health and Community Services. The monitoring data indicate that mosquito numbers were relatively low at the time of the survey, in both the town area and around Il Parpa Swamp.
I t was agreed that there was no immediate need for any adult mosquito control measures resulting from the recent rains. The water in the swamp is relatively cool but i f environmental conditions change and the water temperature does rise, there could be an appreciable rise in mosquito numbers.
The storage of the mosquito larvicide Teknar ( B. t. i . ) for the helicopter applied larval control programs on Il Parpa Swamp was discussed. With the present relatively cool
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weather and the relatively low temperature of the water in Il Parpa Swamp, and the speedy disappearance of surface water from the last heavy rains, i t is not likely that we will require more than one spraying operation of Il Parpa Swamp this financial year. It was therefore decided to leave enough insecticide in Alice Springs for one complete spray of I l Parpa Swamp, with the remainder of the Teknar being forwarded to Darwin so that the insecticide stocks could be rotated more rapidly.
The need for the Regional Health Surveyor to maintain liaison with the Health Surveyor in the Alice Springs Council was discussed. It was reiterated that this Department provides the funding for any helicopter applied vector control operations in the Il Parpa Swamp, as well as providing funds to the Alice Springs Council for adult mosquito control by fogging and for ground operated larval control operations. It is therefore necessary for this Department to verify that these operations are being performed as envisaged. It was suggested that the Regional Health Surveyor for this Department should continue to liaise with the Alice Springs Council on the progress and efficiency of these vector control operations. I t is envisaged that the Regional Office should also conduct periodic and independent checks on some of the mosquito breeding areas to verify that these recommended treatments are in fact achieving the desired results.
5. 0 DISCUSSIONS WITH AlICE SPRINGS HEALTH SURVEYORS
The Senior Health Surveyor for the Alice Springs Council, Mr Owen Harris, was on leave during our visit. Discussions were held with Mr Jim Stott, the second in charge, and Mr Craig Kimpton. Both of these Health Surveyors are relatively new to Alice Springs. The strategy of the present mosquito control program was outlined to them. I t was pointed out that this Department provides the funding for much of the vector control and monitoring operations, and there is a need for continuing liaison with the Department Regional representative, Mr Harold Brown. Mr Stott saw no foreseeable problems with this situation.
6. 0 INSPECTION OF STORM WATER DRAINS AND OTHER MOS QUI TO BREEDING AREAS AROUND ALICE SPRINGS
A general survey of mosquito breeding areas around Alice Springs was conducted with the assistance of Mr Craig Kimpton. Much of the surface water from the preceding rains had disappeared from the storm water drain system.
Drains inspected included the Preist Street drain, the Smith Street drain near the railway yards, The Larrapinta drain, Bradshaw Terrace drain, Chinaman Creek, the Todd River near The Gap, the Bloomfield Street drain, the Casino drain and Charles Creek. Most of the drains and their associated drop structures were free of mosquito breeding.
Mosquito breeding was detected in the Smith Street drain near the railway yards and in the Bloomfield Street drain at one end of the lateral drai n outlets which was overgrown
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with Typha reeds. Cx. quinquefasciatus was the only species recovered from these two breeding sites in the town area. It was obvious from the survey that the various drain outlets to major drains had continued growth of Typha reeds and that these would require s i l t removal and weediciding as soon as possible.
Other areas inspected for mosquito breeding included the railway stockyards in which a tyre stockpile was found to be breeding Cx. guinquefasciatus. This particular mosquito breeding poses no real problem due to the isolation of this area, but should be examined periodically to check for the possible introduction of Aede~ aegypti.
An inspection was also made of the water tank in the Power Station Reserve. A relatively minor leak in the water pipe was discovered, but i t is resulting in water and Typha reeds on the side of the hill in the Power Station Reserve area. This should be reported to the Power and Hater Authority as soon as possible so that the leak can be fixed.
The various borrow pits north of Alice Springs near the Stuart Highway in the vicinity of Charles Creek and the Charles Creek were also inspected. The borrow pits were breeding minor numbers of Cx. annulirostris and this breeding could become a minor problem i f warmer weather occurs.
An. annulipes was recovered in reasonably high numbers from the Charles Creek area, particularly from sites with green filamentous algae. Again, this particular source of mosquitoes would probably have a small to negligible impact on the town, but demonstrates the potential problems associated with a dam in the Todd River i f there are any leaks in the dam structure.
7. 0 INSPECTION OF VECTOR CONTROL EQUIPMENT
which is stored at the Wilkinson Alice Springs Council was inspected It is obvious that the control used for at least two months, and of problems with the equipment The fogging equipment
Street depot of the with Mr Craig Kimpton.
equipment has not been there were a number including:
1 . There was no on/off switch inside vehicle.
2. The battery was completely dead.
3. The vehicle battery was dead.
the cabin of the
4. The insecticide tank seal was non-operational and needs a new seal.
5. The hose to the insecticide tank is perished and needs to be replaced.
6.
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The fogging machine on the back of the stored in the open without any cover.
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vehicle is
7. The safety medicine cabinet had been flooded and the safety equipment was all water damaged.
The insecticide stocks on hand at the Alice Springs Council were also inspected. There was no Teknar on hand for larval control operations, but i t is understood that this insecticide was stored in another area. Maldison ULV stocks included four 20 l i t r e drums, and this stock is adequate for probable mosquito fogging operations. The Teknar ( B. t. i . ) and the backpack for the dispersal of the Teknar are stored at the Council offices. The Teknar for helicopter applied mosquito control operations is controlled by the Regional Health Surveyor, and stocks sufficient for one complete spray operation of Il Parpa Swamp are on hand.
8. 0 DISCUSSIONS WITH OTHER DEPARTMENTAL OFFICERS
Discussions were held with Dr Geoff Hanna of the Communicable Diseases Branch on Ross River virus transmission and malaria cases in the Alice Springs area. Dr Hanna was presented with the latest information on Ross River virus cases in the Northern Territory. The Ross River virus potential was discussed in general terms. Dr Hanna expressed some concern over procedures relating to the recent malaria case in Alice Springs. This was an imported malaria case, and Dr Hanna suggested that more attention is needed at entry points into the Northern Territory, particularly from overseas, to emphasize the danger of malaria to residents returning from overseas. It was mentioned that there is a draft malaria policy and this will be followed up by the Senior Medical Entomologist on return to Darwin.
9. 0 VECTOR CONTROL RECOMMENDATIONS
9. 1 Ground larval control operations
At the time of the visit i t is obvious that mosquito larval monitoring operations have not been carried out since the arrival of the new Health Surveyors in the Alice Springs Council. These officers were unaware of particular inspection sites and operations, and there is a need for a resumption of the regular mosquito checking and control operations, particularly in the Alice Springs drains. The standard of packing and dispatch of mosquitoes from the adult monitoring operations is at present unacceptable and requests have been made for the use of established guidelines.
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9. 2 Aerial larval control
At present there is no immediate need for aerial larval control of mosquitoes in Il Parpa Swamp. This situations may change i f the temperatures increase.
Adequate stocks are on hand for helicopter applied mosquito larval control. It is understood from Mr Harris that the local helicopter company now has the necessary licences to apply Teknar from the air. If mosquito numbers reach sufficiently high levels to warrant mosquito control by larvicide, then the Entomology Branch will recommend action via the Regional Health Surveyor of this Department.
9. 3 Mosquito fogging operations
There is an urgent need to both rehabilitate and house the vector control equipment. Fogging operations may be required i f mosquito numbers increase. The inspection of the Il Parpa Swamp revealed that new fogging routes must be chosen. At present the fogging route does not come close enough to the new mosquito breeding areas that are now associated with the new pipe outlet. A new fogging route is required as close as possible to the pipe outlet and the Typha areas and flooded grass areas. This was discussed with Mr Jim Stott, and i t is hoped that the Council can follow up by installing the basic access for mosquito fogging operations. If fogging operations are conducted on the present fogging route, i t will be a waste of time and insecticide, with very l i t t l e or no reduction in adult mosquito numbers.
CONCLUSION
10. 1 The present mosquito control review indicated particular problems with vector control equipment and with a need for additional training and familiarization on mosquito control operations.
10. 2 A new mosquito fogging route needs to be constructed around Il Parpa Swamp to maximize the efficiency of any vector control operations.
10. 3 Mosquito monitoring operations, and in particular larval checking of the storm water drains around Alice Springs should be resumed as soon as possible by the Alice Springs Health Surveyors.
10. 4 There is no need for a helicopter larval control operation in Il Parpa Swamp at present . There is relatively l i t t l e mosquito breeding occurring in Alice Springs at the moment, despite the recent heavy rains.
