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Northern Territory Department of Health Library Services Historical Collection
3 0820 00019748 8
MOSQUITO INVESTIGATION RANGER MINE JABIRU EAST 23/6/82
·-NT LEPARTMENT OF HEALTH
MEDICAL ENTOMOLOSY SECTION
BACKGROUND
Followingo request from the Biologist, Mr John Bywater, of Ranger Mine, a brief investigation into the current mosquito situation at Jabiru East was conducted on 23/6/82. The mosquito monitoring program carried out by Mr Bywater in conjunction with the Northern Territory Department of Health, had indicated a considerable rise in mos qui to numbers in mid-June. The numbers were such that they constituted a serious pest problem. In 1981 there had been cases of mosquito borne Australian arthritis from the Jabiru area and the indication of high numbers of the vector of this disease warranted an inspection of the current situation with possible recommendations to reduce mosquito numbers.
Investigation of Mosquito Breeding Sites
~ L
The sewerage ponds - a previous survey in August 1981 had detected and recommended the rectification of a number of faults with the sewerage ponds and the effluent dispersal system. The current investigation found the following points required rectification.(a)
(b)
(c)
The primary sewerage pond was heavily overgrown with couch grass and was breeding considerable numbers of Culex annulirostris, the common banded mosquito.
This situation was similar in August 1981.
There was a leak in a pump near the sewerage pond that pumped effluent to the dispersal system. The leak had resulted in an effluent pool that was breeding large numbers of mos qui toes. During periods of rain this effluent would be washed down into No.1 retention pond.
DL HIST 614.4323 WHE 1982
There was large burn hole in the PVC pipe near the fence to the sewerage ponds. This PVC pipe carried effluent to the spray dispersal system. The hole was considerable and resulted in most of the effluent being pumped ~hrough the hole onto the ground with very little effluent reaching the spray dispersal points. This liole had resulted in a large area ~ of effluent . in thick grass and was breeding large numbers of Cul ex annulirostris. With heavy run off with rain this effluent would also be washed down into No.1 retention pond. This burn hole was reported in August 1981. There have been no fires in the vicinity of this pipe this year.
1:) 2
2
( d) A number of burn holes were observed in a spray dispersal system that would allow effluent to pool and nullify the object of a spray dispersal system.
2. No.l Retention Pond and the Upper Reaches of Coonjimba Creek The edges of No.l _retention pond have been considerably colonised by aqu~tic and semi-aquatic plants in the last two years and this area was breeding considerable numbers of Culex annulirostris. The faulty effluent dispersal system is likely to have aided some of this heavy vegetation growth by increasing the nutrient levels in the pond. The marginal areas of No.l retention pond are shallow and extensive and this situation will lead to increasing amounts of vegetation growth and mosquito breeding. Ideally) this retention pond should have steep sides around the margins to prevent large areas of vegetation growth and hence mosquito breeding.
Further upstream in Coonj imba Creek below the tailings dam there is considerable amounts of water in the creek line with considerable vegetation growth and this is resulting in mosquito breeding. There is a possibility that the ground water in this area is being maintained by the tailings dam.
·3. Djalkmara Billabong - there has been a minor increase in the amount of reeds around this billabong since 1981, and this increase is presumably from the reduction of the buffaloes. The billabong was drying up at the time of the inspection and there are only small areas that were suitable for mosquito breeding. The pumping of the water from a holding pond below No.2 retention pond was enabling the billabong to dry out more rapidly and was resulting in .the relatively vegetation free margin.
Currently) this billabong is only a minor source of mosquitoes but it could become a more important source as the billabong becomes more colonised with aquatic reeds.
4. Georgetown Billabong and Creek - the edges of Georgetown Billabong have shown a dramatic increase in the amount of reed growth alon~ the @~ges. The previous inspection in 1981 had only revealed small amounts of Eleocharis §J2_.
reeds at the edges of the billabong and now there is a considerable margin of reeds. The increase in this thick reed growth has resulted in a considerable increase in the available mos qui to breeding sites, especially for Culex annulirostris. This species was breeding amongst the lodged reeds which were offering protection from the predaceous beetles, bugs and fish. The upper reaches of ' Georgetown Creek was drying out rapidly and because permanent aquatic vegetation w~s not established in these areas, they were not considerable sources of mosquitoes. ,, 5. Coonj imba Billabong - .the Coonj imba Billabong had shown
an increase in the growth of Eleocharis reeds since the last inspection but the increase appeared to be only minor. This may be because Coonj imba Creek has had relatively little buff ala disturbance over a number of years due to the proximity of the housing area. Although no Coquillettidia or Mansonia larvae were found in this
area the high number of adult mosquitoes of these species indicate that this billabong is a major source of these two species. These two species are very closely associated with well established areas of Eleocharis reeds.
Adult Mosquito Catches
The highest catches of mosquitoes were made in the upper reaches of Coonjimba Creek below the tailings pond. (See Table 1). This indicates that this area .and the upper reaches of the No .1 retention pond are the major sources of mos qui toes for the Ranger area. This site offers ideal mosquito breeding and harbouring sites due to the thick vegetation along the edges of the pond and in the creek line. The next highest catch was in Coonjimba Creek below the No.l retention pond and this again offered ideal mos qui to breeding and harbouring sites. The Coonjimba Billabong area appears to be the major source of Coguillettidia and Mansonia mosquitoes and this is confirmed by the presence of well established Eleocharis reeds that are closely associated with the larvae of these two species. Both Coguillettidiq and Mansonia mos qui toes were biting in the vicinity of Coonjimba Billabong during the day, indicating that this area was an important day time harbouring
·site for these mos qui toes. The relatively high catches of mosquitoes at Honeyeater Street in the residential area indicates that considerable numbers of mosquitoes are invading the residential areas at distances away from the billabong and creek line. This invasion would be due to the very high numbers of mosquitoes at the sources and the harbouring areas, but is also a reflection of the suitable day time harbouring sites in the residential area that have resulted from well watered and vegetated gardens. Figures of over 100 Culex annulirostris mos qui toes per trap per night are considered pest levels, so figures of up to 600 in the resential area constitutes a serious pest problem. The trap at Georgetown Billabong indicated this area as a source of Culex annulirostris for the mine site, although it was not as large a source as Coonj imba Creek and Billabong. As the reeds become more established in the Georgetown Billabong area, the numbers of mosquitoes that originate from this area will increase. The numbers of mosquitoes recorded near the Ranger Mine gate indicated that there could be pest numbers of mosquitoes in the mine site itself.
Potential Disease Problems
Apart from the very high pest levels of mosquitoes, there is a potential for the transmission of Australian Arthritis and Australian Encephalitis. The vector of these two diseases, Culex annulirostris, is the most iommonly caught mosquito in this area. Australian Encephalitis has been recorded from north-west of yJestern Australia for the last few years, and there is a potential for the transmission ~f this disease in the top end of the Northern Territory. The artificial situation that is developing in No.l retention pond, with its wide areas of shallow water and thick vegetation growth, is reminiscent of the very large breeding areas that have been created on the Ord River system in the north-west of Western Australia. From January to August 1981, there were at least
4
five cases of Australian Arthritis in the Jabiru area. The five confirmed cases may only be a proportion of the actual number of cases of this disease and increased high levels of Culex annulirostris increases the potential for the trans- mission of this disease. A proportion of the mosquitoes caught during the current survey were collected live and processed for virus. These are still beirig processed but a negative result for virus from the sample will not necessarily mean that there is no virus present in.the area. The presence of Anopheles species in the area indicate that there is potential for malaria transmission to occur .if cases of malaria are imported to the Jabiru area.
Suggested Mosquito Control Measures
1. Rectify all the faults in the sewerage ponds and sewerage dispersal system.
2. Establish, as soon as possible, access tracks to conduct mos qui to fogging operations around the most important mos qui to breeding and harbouring areas as indicated on the accompanying map. The most important priority would be to construct access and to carry out fogging around Coonj imba Creek and No .1 retention pond. The mos qui to access tracks would be need to as close to the breeding and harbouring areas as possible, and the suggested route is indicated on the map at the edges of the seasonally inundated area.
3. Institute a weekly mosquito fogging program using a vehicle mounted Leco ground aerosol insecti:ide machine using Malathion insecticide. The mos qui to fogging program should be tied closely to a mosquito monitoring program to be carried out by Mr Bywater. The minimum sampling sites necessary would be one at Coonjimba Creek below No.l retention pond and one at the mine site gate.
The possibility of sharing the Jabiru Town Development Authority insecticide fogging machinery needs to be investigated.
4. The edges of the No.l retentio~ pond should be engineered to provide a steep sided margin that will not encourage emergent vegetation.
Discussion with Ranger Personnel
Discussions were held Mr Ian Macguire, the Engineer in charge of maintenance, Mr Peter Lucas, Environmental Superintendent, and Mr John Bywater, the Biologist for Ranger. The discussion concluded that there was a problem,, and that the access tracks for fogging appeared necessary. }Mr Bywater agreed that he could continue to monitor the mosquito problem in co-operation with the North~rn Territory Department of Health. Ranger do not have the necessary equipment for adult mos qui to fogging and the suggestion of borrowing the machine from the Jabiru Town Development Authority remains to be followed up.
Conclusion
There are very high levels of vector mosquitoes in the Jabiru East area which constitute serious pest problem and a potential heal th problem to the residents and workers of Jabiru East. There are serious faults in the sewerage scheme that are compounding the mosqµilo problem and which need rectification. It is recommended that access tracks· should be established around both sides · of Coonjimba Creek, No.l retention pond and areas of Georgetown Creek and Georgetown Billabong. A fogging program on ,the above access tracks around the important mosquito breeding and harbouring is recommended once per week and based on a mosquito monitoring program.
P. Whelan
SENIOR MEDICAL ENTOMOLOGIST
Enc
Species Map No.
An annulipes An bancroftii An hilli
An meraukensis An. novoguinensis Cx annulirostris Cx bitaeniorhynchus Cx quinquefasciatus Cx pull us
Cq. xanthogaster Ma. uniformis Ad catasticta Cx sitiens
TOTAL
MOSQUITO COLLECTIONS RANGER MINE AND JABIRU EAST 24/6/82
Coonjimba Billabong
1
7 20
2,126 3 8
278 245 12 1
2700
NUMBER OF FEMALE MOSQUITOES PER CO
2 TRAP/NIGHT
Jabiru East Honeyeater St
2
5 4
655
53 6 35
758
F~nce Sewage Ponds
3
8
4
430
24
10
476
Coonjimba Ck Tailings Dam
4
21 1
18 1 6,000
87
17
18
6163
Ranger Mine Gate
5
32
4
480
16
532
TABLE I
Georgetown Billabong
6
23 12
18
950
2 26 8
1039
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