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Northern Territory Department of Health Library Services Historical Collection
DL HIST 595.772 WHE 1978
PRELIMINARY MOSQUITO SURVEY NAB.ARLEK NT
SEJYFEMBER 1978
For more information contact:
Territory Health Services Medical Entomology Branch PO Box 40596
CASUARINA NT 0811 Telephone: 22 8333
Peter Whelan
Senior Medical Entomologist
OoS2o
HISTORICAL COLLECTION
PRELIMINARY MOSQUITO SURVEY NABARLEK N.T.
INTRODUCTION
SEPTEMBER 1978 Medical Entomology Section, Department of Health, Darwin.
Queensland Mines Ltd., proposed to mine, concentrate and export uranium from a deposit discovered in 1970 at Nabarlek, Arnhem Land, Northern Territory. The mining will be by conventional open cut techniques over a period of 2 years and processing will occur at the site for a period of 8-10 years. A temporary construction camp will be established for approximately 200 people, while a permanent work force of about 100 people will be mostly flown to N abarlek from Darwin on a routine basis. In December 1977, Queensland Mines published the "Draft environmental impact statement" for the Nabarlek project. In this report there was no mention of potential or actual mosquito breeding sites in the area, although the report did list in its references a CSIRO report, on an insect survey conducted over a wide area of Arnhem Land 1972-73. This CSIRO report stated that a total of 24 species of mosquitoes were collected in the Arnhem Land area on three visits but did not refer to the Nabarlek area specifically. Detailed knowledge of mosquitoes, including their occurrence at different times of the year, the species present, the relative numbers, and the actual breeding sites, was needed for the N abarlek area. The Department of Health was approached by the Environmental Officer of Queensland Mines, after preliminary talks on health matters, and requested the Department to conduct entomological investigations in the area.
It is proposed to conduct at least three investigations at Nabarlek at different times of the year.
This first preliminary survey is timed to coincide with the driest period of the year. Other surveys will be conducted in the middle of the wet season and after the wet season to establish base line information of mosquitoes in the area.
METHOD
Three different methods of collecting mosquitoes were used in order to establish the presence of as many different species as possible. Mosquito larval surveys were carried out by sampling as many different aquatic environments as possible, using a metal dipper. Attention was given to Coopers Creek as this is the nearest permanent water to the proposed development. The larval survey will determine actual breeding sites for each species.
Man biting collections were carried out by exposing legs after sundown, in likely areas, and aspirating the biting mosquito into small collection vials using a mechanical vacuum aspirator.
Two collectors caught at each site in order to eliminate individual differences. Light trapping for mosquitoes was conducted with the use of 6 volt 3 watt fan light traps. The mosquitoes were collected live into plastic collecting containers, killed, pinned and transported back to the laboratory for identification.
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RESULTS AND DISCUSSION 1.0 Collection results
1.01 Species collected
The results of the survey are tabulated in Tables I - V and located on Map 1. The list of all species of mosquitoes collected in the area is found on Table V and includes 16 species. Some of these species are awaiting confirmation. This list of species includes 3 Anopheles species which are regarded as potential malaria vectors, although the suspected principal malaria vector in the Northern Territory, Anopheles farauti, was not collected.
Also collected was Cu/ex annulirostris, the vector of Murray Valley encephalitis virus and , Ross River virus. The species in the Cu/ex "annulirostris group" including Cx. "normanton sp
near annulirostris NT form" are still taxonomically unclear and nothing is known of their disease vector potential.
1.02 Larval survey
The larval survey (Table 1) outlines the breeding sites of the different species. From the table it can be seen that Anopheles annulipes was found breeding at the edges of streams and creeks, either with or without marginal vegetation and algae. In some instances this species was found on top of floating algae in the pools of Coopers Creek in which there were numerous fish. When the larvae were displaced from the algae they were quickly consumed by the fish, demonstrating the very good biological control that is present in these pools.
Anopheles annulipes was found in a mining costean, together with Cx. "annulirostris gp."
mosquitoes, demonstrating the potential for the creation of man made mosquito breeding sites.
Anopheles bancroftii was found in the more shaded aquatic vegetated pools on the creek west of the Nabarlek mine site and these sites would be expected to increase in the wet season.
Cu/ex annulirostris was found at the edges of vegetated pools in the creeks, in wheel ruts, costeans, and hoof prints, demonstrating the wide range of possible breeding sites of this species. The species is likely to take advantage of mining disturbances and the subsequent creation of mosquito breeding sites. Most of the other species of larvae were found in vegetated margins of the creeks and were only in relatively small numbers due to fish predation. Due to the fact that September is the driest period of the year, there were only a few breeding places available for mosquitoes. The most prolific mosquito breeding sites available at this period were the mining costean, the septic tank and the vegetated pools in the creeks. Most of the area is relatively free draining and there are no large areas of swamps nearby. It would be expected that Coopers Creek in the wet season would be a larger source of mosquitoes due to the creation of shallow flooded areas at its boundaries, but this would need investigation. Areas of the creek that have been formalised, such as the sand walled tanks in the bed of the creek, showed no mosquito breeding. This was due to the ease of fish predation at the steep, vegetation free edges.
1.03 Man biting collections
The man biting results on Table II indicate very low levels of mosquitoes at Nabarlek at this time of the year. This is a reflection of the small number of breeding sites available, and the dry, open nature of the country, which would result in low survival rates for adult mosquitoes.
Man biting catches were only made at the edge of Coopers Creek, indicating that adult mosquitoes are restricted to the more moist, humid conditions near the creeks. The new
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construction camp and the initial camp were free of mosquito biting activity due to their distance between the breeding sites and the dry nature of the intervening country.
This is reinforced by the lack of mosquitoes in the light trap collection at these two sites. The biting of Tripteroides punctolateralis in the day at the initial camp is caused by the close proximity of the breeding sites of this species, namely the septic tank and water tank, and these breeding sites could be easily prevented.
1.04 Light trap collections
The mosquito light trap results on Table ill again show that the most mosquitoes and species are to be found near the creeks. The most frequent mosquito species found in the light trap is Anopheles annulipes which is a reflection of the suitable breeding sites available for this species. As this species possesses no siphon in the larval stage, it can exploit the extreme edges of pools and on top of floating algae, which are unsuitable for Cu/ex annulirostris with a long siphon. The numbers of Cu/ex annulirostris are very low but this species is likely to show much higher numbers during and after the wet season when there would be more shallow vegetated creek margins, depressions and temporary pools available.
Aedeomyia catasticta is not a man biting species and its presence in the light trap indicates that there are suitable green filamentous algal areas in the pools along the creeks. The presence of Anopheles hi/Ii in the light trap is unusual as it is usually a brackish to salt water breeder. This species may become more numerous in the wet season when more winds and suitable coastal breeding sites occur, and humid conditions enable it to penetrate further from its normal habitats.
1.05 Container survey
The larval mosquito survey of containers at Nabarlek showed few artificial containers and many of these were dry due to the absence of rain. The elimination of artificial containers should be encouraged and suitable areas for the land fill of disused containers would be necessary in the coming development. In particular, drums, tyres, tin cans and old car bodies and machinery would need to be land filled to eliminate man made container breeding mosquitoes.
2.01 Mosquito prevention
In the initial camp that was in use during the time of the survey, there was little insect screening on some of the demountable sleeping units and the doors had to be kept open for ventilation. This was of little consequence during the period of survey, but during the wet season, mosquito-numbers would be expected to increase and then insect screening would be a necessity to prevent annoying pest mosquitoes, as well as reducing the possibility of mosquito born disease. Of particular concern in the mining camps is the re-establishment of malaria, as it is probable that mining personnel will arrive from overseas malarious areas and may harbour the malaria parasites in their body. Besides adequate mosquito protection during the night it will require malaria checks prior to entering the region, on the same lines as those conducted at Nhulunbuy and Groote Eylandt.
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2.02 Artificial depressions
At the time of the survey at least 20 large mining costeans were obseived. Of these only one was found with water in it and this was breeding large numbers of mosquitoes, due primarily to the lack of fish in the costean.
These areas would fill with water after rain and create a large amount of mosquito breeding.
It would be recommended that any such structures be filled in soon after their use. Buffaloes and their wallows create similar situations near the margin of Coopers Creek and the discouraging of buffaloes near the towns would be advisable.
2.03 Sewage ponds and effluent
In the draft environmental statement it was mentioned that sewage ponds were to be constructed and that the resulting excess efiluent would be directed into Buffalo Creek. This creek would also receive excess water from the retention ponds (see Map 2). This would result in a more permanent creek which at present is completely dry. Any addition of sewage efiluent to such a creek usually leads to greatly increased mosquito breeding, particularly for Cu/ex annulirostris, the vector of Murray Valley encephalitis. It would be recommended that, to reduce this problem, the sewage ponds be made of a greater capacity than would normally be the case, so that there would be more evaporation and less effluent release. The efiluent ponds would also need wide concrete aprons or vertical concrete sides to eliminate grass growth and subsequent mosquito breeding, as effluent ponds are one of the most prolific breeding sites of mosquitoes.
2.04 Impoundments
Normal retention ponds are less likely to breed mosquitoes but their banks should be as steep as possible to ensure that their will be minimal grass margins. These margins may require grass removal or control from time to time if mosquito breeding is detected.
In the draft environmental statement there is mention that a weir on Buffalo Creek may be necessary. This weir should be constructed in a site where it will not form shallow vegetated margins in its upper reaches, or it will create suitable mosquito breeding sites. Ideally it would be better if the weir formed part of a steep formalised dam that would not create shallow grassed margins.
2.05 Introduction of new species
If the uranium is shipped by boat from Laterite Point then additional precautions are needed to eliminate man made containers in this area to reduce the possibility of a successful re- introduction of Aedes aegypti, the dengue mosquito. This species is in Torres Strait and could be reintroduced into the Northern Territory by shipping. It was noted that Aedes tremulus and Tripteroides punctolateralis were collected emerging from a septic tank. This habitat is usually a prolific breeding place for Cu/ex fatigans, the brown house mosquito, which is a troublesome pest species in most urban areas. It appears that this species is absent from the N abarlek area and efforts should be made to ensure that it is not intr9duced. The most likely method of introduction of this species would be in tyres or containers with water, especially tins of plant cuttings. A simple educational sheet about mosquitoes aimed at residents would be a valuable aid to mosquito elimination and control.
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2.06 Mosquito Control
Even if adequate mosquito prevention methods are undertaken there will still be a need for mosquito control at certain periods of the year.
For efficient mosquito control there needs to be a vector control squad of at least two people set up, together with adequate transport and control equipment. This squad would search for new breeding places of mosquitoes that may be created, control these and other breeding places, and carry out a monitoring and adult mosquito control program when required. The squad would need granule insecticide application equipment and ultra low volume aerosol adult mosquito control equipment to control both larval and adult mosquitoes. Training of such personnel can be carried out at the annual mosquito control course in Mildura, organised by the Commonwealth Department of Health. Mr Bill Fox, for Queensland Mines, has undertaken to rectify the current mosquito breeding in the mining costeans and the septic tanks.
CONCLUSIONS
1. A tentative list of 16 species of mosquitoes is recorded for the Nabarlek area, including potential vectors of malaria and arboviruses such as Murray Valley encephalitis.
2. The mosquito numbers, as judged by man biting, larval and light trap collections are very low at this time of the year due to the lack of available sites, biological control, and unfavourable environmental conditions.
3. The most prolific breeding sites at the moment are the pools in the beds of the creeks.
Future surveys are needed at other times of the year.
4. There a number of artificially created mosquito breeding sites, including mining costeans, vehicle ruts, septic tanks and domestic water tanks that need to be eliminated.
5. During the present survey, mosquito breeding and activity was largely restricted to the creek systems containing pools.
6. Mosquito protection including screening will be needed in future living quarters.
7. Health checks will be necessary to prevent the re-introduction of malaria.
8. During the future development, the creation of new breeding sites of mosquitoes can be caused by sewage ponds, sewage effluent release, retention ponds, artificial depressions, disused containers and impoundments. Efforts are needed in the planning stage to prevent new breeding sites from being created.
9. A permanent vector control squad should be set up with adequate transport and equipment to detect and control mosquitoes.
Peter Whelan
Senior Medical Entomologist
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ACKNOWLEDGMENTS
It is wished to thank Mr Peter Rafferty and Mr Bill Fox of Queensland Mines for their help and hospitality in conducting the present survey.
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TABLE I
LARVAL COLLECTIONS NABARLEK 18 - 20 SEPTEMBER 1978
SITE LOCATION BREEDING SITE SPECIES NO.
Site 1 10 km south Leaf edge of creek, flowing, An. annulipes of airstrip well defined.
'
Site 2 3kmSE Hoof print near wallow. Cx. annulirostris
of airstrip Paperbark depression.
Site 3 No 1 1.5 km south Deep clear leaf stained pooL Cx. sp. 32 of airstrip in algae at edge of creek. Cx. hilli No2 II II On top of floating algae An. annulipes
edge pool in creek.
No3 II II Clear leaf edged pool An. annulipes
in creek. In algae.
No4 II II Leaf pool at base oflog Cx. hi/Ii in creek bed. An. annulipes No5 II II Wheel rut 1n clay bed Cx. sp. 32
of creek. Cloudy water. Cx. annulirostris An. annulipes No6 II II Large, leaf stained pooL An. bancroftii shady leaf edges. An. annulipes No7 II II Small leaf stained pool Cx. hilli
with green algae. An. annulipes Site 4 No 11 3 km NW from Deep aquatic vegetated An. bancroftii
initial camp site pool in creek line with Cx. Normanton sp. NT reed and algae. Ad catasticta
Semi shaded. Fish. Cx. hilli
Cx. annu/irostris No 12 II II Edges of deep, reed, aquatic An. bancroftii
weed pool amongst algae. An. annulipes
1 Clear water. Cx. Normanton sp. NT
Ad. catasticta Cx. sp. 32 continued over page
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TABLE I continued
SITE LOCATION BREEDING SITE SPECIES NO.
Site 5 7.6 km north of Large cut off pool with An. annulipes airstrip on leaf margins.
Coopers Creek
Site 6 6 km west of Sandy creek bed - dry.
initial camp in gorge area
Site 7 No8 1 km SE of initial Small green Cx. vicinus-starkeae camp in Coopers :filamentous algal An. annulipes
Creek. grass pool. An. novaguinensis
No9 II II Thick brown algae, Cx. Normanton sp.
pool cut off from NT form
large pool. Cx. Normanton sp.
Qld form Cx. sp.
No 10 II II Edge of pool among An. annulipes green :filamentous Ad. catasticta algae and grass.
Site 8 Costean opposite Deep costean with An. annulipes construction camp site floating grey algae Cx. annulirostris 1.5 km north of and clay suspension. Cx. Normanton sp.
airstrip
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TABLE II
MOSQUITO MAN BITING RESULTS NABARLEK 1978
DATE TIME COLLECTORS SITE NO. LOCATION
18/9/78 1900 2 Initial camp site
1930
19/9/78 0730 1 Initial camp site,
bathroom.
19/9/78 1200 1 Initial camp site,
kitchen.
19/9/78 1912 2 Site 3 Edge of Coopers
1927 Creek 1. 5 km south
of initial camp site.
19/9/78 1945 2 Near site 8 At new construction
2000 site.
TOTAL
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Anopheles Coquellittidea Cu/ex annulipes xanthol!aster annulirostris
Nil
1 1 I
Nil
1 1 1
...
Aedes normanensis
I
1
Tripteroides
punctolateralis TOTAL
1 1
2
0 1 1 4
0
6
Medical Entomology THS
0 0
1/)
~
TABLE ID
MOSQUITO LIGHT TRAP RESULTS _NABARLEK 18- 20 SEPTEMBER 1978
DATE SITE
SET NO. LOCATION An. hilli An. annulipes Cx. annulirostris gp. Cx. hilli
F M F M F M F M F
Initial camp site 18/9/78 at south edge. Nil
Edge of Coopers Creek 1.5 km
19/9/78 3 south of airstrip 5
Edge of creek with aquatic vegetation 3 km NW of initial
19/9/78 4 camp 1 1 3 1
Edge of Coopers Creek 7.6 km
19/9/78 5 north of airstrip 10 1 2
Edge of road near
construction
19/9/78 8 camp Nil
SUB-TOTAL 1 0 11 1 8 0 1 2
TOTAL 1 12 8 3
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...
Cx. sp. Cx. bitaeniorhynchus Ad. catasticta
M F M F M
1
1 6
1 0 1 0 6 0
1 1 6
•
Cq. xanthogaster TOTAL
F M
1
1
2 0
2
Medical Entomology THS
0
7
7
20
0
34
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TABLE IV
LARVAL MOSQUITO CONTAINER SURVEY NABARLEK
NO. DATE SITE CONTAINER SPECIES
SEARCHED
1 20.9.78 Initial camp Disused, open water tank. Tr. punctolateralis larvae (2 adult females resting in tank)
2 II II II Disused screened water Nil
tank.
3 II II II Camp water tank - used. Nil
Well sealed.
4 II II II 44 gall. drum near toilet. Nil
5 II II II 44 gall. drum near toilet. Nil
( 1 adult Tr. punctolateralis resting in drum)
6 II II II Septic tank - not inspected. Very many
Tr. punctolateralis and lesser no. of Ae. tremulus emerging via crack.
7 II II II Septic tank sealed. Nil
8 II II II 44 gall. drum near showers. Nil
9 II Aboriginal camp Water tanks -dry. Nil
10 II Core shed Core trays. Nil
i
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TABLEV
LIST OF MOSQUITO SPECIES - NABARLEK 18 - 20 SEPTEMBER 1978 Man Biting Resting Larval Light
Trap
Anopheles annulipes ./ ./ ./
Anopheles hilli ./
Anopheles bancroftii ./
Anopheles novaguinensis * ./
Cu/ex annulirostris ./ ./
Cu/ex Normanton sp. NT form ./
Cu/ex Normanton sp. QLD form ./
Cu/ex hilli ./ ./
Cu/ex bitaeniorhynchus ./
Cu/ex sp. 32 ./
Cu/ex vicinus-starkeae ./
Aedes tremulus
*
Aedes normanensis ./
Tripteroides punctolateralis
*
./ ./C oqui lie ttidea xanthogaster ./ ./
Aedeomyia catasticta ./
*
Awaiting confirmation oridentification by Dr E. Marks Q.I.M.R• I
,.•
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