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Northern Territory Department of Health Library Services Historical Collection
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MOSQUITO CONTROL TENNANT CREEK
Report on a visit to Tennant Creek 27/9/78 by medical entomologist.
1. The previous entomology inspection of Tennant Creek was carried out in September 19760 During this visit there were a number of mosq1iito breeding sites located, including septic tanks, leaking water meters and fire hydrants, and storm water dr.:::.ns.
Potential mosquito breeding was noted in the upper reaches of the proposed recreation lake and the last ponds at the sewage treat.~ent works.
2. The present inspection was carried out in co-operation with
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Mr Dave Thomas, Senior Health Inspector, Tennant Creek. Mosquito breeding was found in a number of sites that had previously been located or have been located by Mr Thomas. These are detailed below.
2.1 Storm water drains Location of Drain
a) Stuart H1way adj.
to Inland Hission b) Maloney St adj to warramunga Village
c) Weaber St and Kathleen St
d) Staunton St
e) Ext of Stuart St next to Purkiss Reserve
f) Blain St, Stuart B\·1y
Description Mosquito Larvae present Pool near culvert 'Culex fatigans
silted up & grassed
Cut off pools o ,Culex annulirostris Rubbish & s i l t
present
Pooling at culvert silted up
Deep drop pit pool with silt & grass
Pooling with silt and grass
Dry but silt and grass problems
I Anopheles annulipes
Anopheles annulipes
At-10pheles annulipes
Nil
Pooling near the storm ~.Jater drains is the result of dry season flow from watering and r.·rnshing activities o The sites that are listed above are mostly limited in area, and occur where the covered concrete
pipe drains emerge to join the large open earth storm channels. At these points there is gouging which has produced a water filled depression. The depression is bl¢cked on the downstream side by s i l t and grass. In nearly all of these sites the resulting blockage by silt and grass in the earth channel has dammed water up in the pipe extending back beneath roadways. This results in inefficient draining and at the same time creates a permanent water evnironment in the pipe which promotes mosquito breeding in the pipes and is
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difficult to both detect and controlo It is suggested that to prevent this occurring the areas of the termination of all those storm water pipes in the earth channels be concreted for at least 5 metres do~mstream so that gouging doesn't occur and the water doesn •t back up in the pipes o ''The area near the termination of these pipes, even after concreting, will need annual desilting with equipment such as a front end loader. The drop pit structure at Staunton Street has been previously pumped out following
Mr Thomas' suggestion, and this would need to be carried out regularly as needed until the design of this site could be
solvedc It is urged that the above matters be taken up officially with the local relevant authorities to ensure planning and
estimates can be carried out.
Of the mosquito species listed above, Culex annulirostris, (the conu~on banded mosquito) is of concern as i t is the vector of
Australian encephalitiso Culex fatigans can transmit this disease in the laboratory so i t is a potential vector of the above disease.
There has been an outbreak of Australian Encephalitis, t'lith a number of human cases, in early 1978 over a large area of N-W Australia extend_:_ng from Balgo Hills, Kununurra, to Port Hedland.
The above area is similar in parts to the semi arid region around Tennant Creek. It is thought that the outbreak was the !:"csul t of unseasonal rain in the area 'and demonstrates that a similar out- break could include the Tennant Creek area in the future ..
Any elimination of suitable mosquito breeding sites close to hl.llnan settlement is viewed as a necessary measure to reduce the potential of this disease. The three mosquito species found in the tovm are also species that readily bite people, so elimination of these breeding sites will reduce mosquito pest problemso
2.2 Sewage Lagoons
On the previous inspection in 1976, only the first two lagoons were full and mosquito breeding was not found in them, largely
due to the vertical concrete sides and wave action making conditions unsuitable for mosquito larvae.
On the current inspection one of the lagoons into which the effluent passes after treatment in the first two lagoons ,was found to be breeding Culex annulirostris and Anopheles annulipes. This mosquito breeding was occurring in the grass and vegetated edges of this partially filled lagoon, below the level of the sloping concrete aprons at the margins. Dead vegetation was present inward from the waters edge, indicating that the pond was not cleaned up before effluent commenced flov:ing into i t . This vegetation had the effect of re~ucing suitable wave action which would have aided in preventing mosquito breeding. Vegetution including grass was growing readily at the edge of the effluent
because the very slowly filling pond had resulted in a stable effluent- earth margin. This grass growth could have been prevented if the sloping concrete apron had been extended at least a metre lower dmm., This modified design \·1ould be appropriate in similar sewage ponds in arid areas where ponds take a considerable time to f i l l up. When
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the currently filling pond is full, the overflow will be directed into a similar pond in ·which the s<J.me problems occur. 'As well , the latter pond has heaps of earth that will create grass edged islands in the bottom of the pond as i t is filling, and this will be conducive to mosquito breeding. It is reco~mended that the latter pond be cleaned out before the effluent begins to flow into i t . At lease as a temporary measure, until the ponds reach capacity strips of black malthoid sheeting around the margins would prevent grass growth and raosquito breeding. Otherwise regular inspection and insecticide treatment of this pond would be required. If the margin stabilizes at a level below the concrete apron, this treatment may need to be carried out over a long period. As Tennant Creek
continues to be
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2*fi; ~g connected to the sewage system, i t is expected that effluent will begin to flow into the largeevaporation impoundment at some future date.. 1>7hen this occurs i t will create thickly grassed, shallow swampy areas which wil l be ideal for Culex annulirostris. As the area is so flat this mosquito breeding could be extensive and the resulting high numbers of
mosquitoes could easily influence the township. Now is the appropriate time to examine the options of re-use of the effluent, before a
problem similar to that which exists in Alice Springs is created.
Trials of the re-use of the effluent in Alice Springs has already shown promise in the growth of Eucalyptus trees and dateso It is suggested that the Council or other authorities be approached on the feasability and design o~ re-use methodso
2 o3 Domestic ~'later Tanks
Most of Tennant Creek is now on a reticulated water supply but many domestic water tanks are s t i l l present in the town. From a sample inspected, i t appears that some have been marked for removal but although holed, one was s t i l l holding about 10cm of water and had evidence of recent mosquito breedingo It is under- stood from residents and Mr Lyell Campbell of Transport· and Works, that the tanks have been marked for removal for a number of years, yet no action has been taken • .Most of these would be on Common- wealth or Housing Conm1ission property. On other properties water tanks are s t i l l in use for watering, and two of these tanks were not screened. As they were full, no mosquito breeding was found, but when the level recedes they will be sources of mosquitoeso Water tanks are of particular concern as they are the principal breeding site of Aedes aegypti, the dengue fever mosquito, and with numbers of suitable breeding sites present, this species could be reintroduced into Tennant Creek. A survey is needed in Tennant Creek of all rain water tanks to list removal or repair measures needed to be carried out. It is suggested that this could be carried out by Mr Thomas of the Health Inspectors section and the appropriate measures taken.
2.4 Septic Tanks and other Mosauito Breedina Sites
A nmnber of septic tanks in the Tennant Creek area that were previously problems have now been eliminated by connections to the sewage system.
This eliminates many of the sources of Culex fatigans, the brown house mosquito, which would be the main vector of heartworm of dogsQ Mr Thomas mentioned that the remaining septic tanks will soon be eliminated as more sewage connections are madeo The leaking fire
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hydrants and water meters that \·Jere previous problems have now been rectified by the Transport and Viorks Department. Excess watering in some areas, especially on parks a...'l.d public grounds adds to the storm '.vater in the drains. With closer attention to watering much of the dry season flow in drains, and subsequent mosquito breeding, could be el.:kminated. :11r Thomas had indicated that he is currently advising various authorities on the consequences of over watering in regard to mosquito breeding.
The Town Dam was found to have no mosquito breeding due to its steep earth sides and fluctuating, vegetation-less margins. TLe
swimming hole on tl1e Tennant Creek was not breeding mosquitoes for the same reason.
Work has not yet started on the propos2d recreation lake but a monitoring of the upper reaches, possi:)ly :.JY the Health Inspector Section could soon establish if mosc::_uito breeding occurs when the dam is completed.
A mosquito light trap was delivered to Nr Thomas who will undertake a weekly operation of the trap during the rainy season to establish species and relative numbers of mosquitoes present. The catches wi l l be forwarded to the entomolo0y sect ion Dar'.·1in for sorting.
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Fly BreedinqThe Associated Meats Abattoir at t:hc south end of town Has examined as one of the likely sources of the house fly problem in Tennant Creek. The area 't1as inspected with Mr Don Schillington, the manager.
Considerable fly breeding was loc.J.tcd in a trench filled with effluent and vegetable waste matter.
Mr Schillington i:.,1as co-operative and agreed to install a flexible hose to a pump and distribute the effluent and vegetab_;I.e '.vaste at different sites ovGr the ground on a frGquent cycle so that the effluent would dry up and eliminate the fly breeding.
Peter :,fuelan
S:2NIOR MEDICAL ZNTOMOLOGIST
