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Northern Territory Department of Health Library Services Historical Collection 0 0-7,::;_ 7 HISTORICAL COLLECTION
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For more Information Contact: ' '' I j,t 1· Department of Health and Community Services
: 'I• Medical Entomology Branch GPO Box 1701 •I
' DARWIN NT 0801 • I
Telephone 22 8333 Peter Whelan Senior Medical Entomologist , ..
'DLHIST 614.4323 .J WHE 'i 1990 ,.. I 1l1[1l1~11i1 ~lllf1111ij1i 1111]1i11~1111 ~1~1ij 111111~11 3 oa20 00019002 o 1':3~()
MEDICAL ENTOMOLOGY INVESTIGATION OF PROPOSED JUNCTION WATERHOLE DAM ON THE TODD RIVER .
PETER WHELAN SENIOR MEDICAL ENTOMOLCGIST MEDICAL ENTO'v10LCGY BRANCH NORTHERN TERRITORY DEPARTMENT OF HEALTH AND COMMUNITY SERVICES MARCH 1990
TABLE OF CONTENTS PAGE
1. 0 BACKGROUND 1
2. 0 FIELD INVESTIGATIONS 1 2.1 Aim 1 2. 2 Surface Water Survey 1 2. 3 Larval Sampling Method 1 2. 4 Adult Sampling Method 2
3.0 RESULTS 2 3. 1 Surface Water Survey 2 3. 2 Larval Sampling 3 3 . 3 Adult Sampling 4
4. 0 DISCUSSION 5 4 . 1 Present Mosquito Breeding Habitats 5 4. 2 Potential Mosquito Breeding Habitats 6 4. 3 Potential Public Health Problems 8 Posed by Biting Insects 4.3.1 Epidemic Polyarthritis 8 4.3.2 · Australian Encephalitis 8 4.3.3 Malaria 8 4.3.4 Nuisance Insects 8
5. 0 MEASURES TO REDUCE OR AVOID MOSQUITO BREEDING 9 5. 1 Design Features 9 5. 1 . 1 Fish Transfer 9 5. 1 . 2 Stock Exclusion 9 5 .1 .3 Water Level Manipulation 9 5. 1 . 4 Sediment Traps 9 5. 1 . 5 Prevention of Leakage 9
5. 2 During Construction 1 0 5. 2. 1 Vegetation Removal 1 0 5 .2.2 Flotsam Removal 1 0 5 .2. 3 Mosquito Monitoring 1 0
5.3 After Construction 1 0 5 .3. 1 Prevention of Nutrient Input 1 0 5. 3. 2 Weed Control 1 0 5. 3. 3 Flotsam Removal 1 0 5. 3. 4 Larval Mosquito Control 1 0
10/12/90 TABLE OF CONTENTS (continued) PAGE
6.0 MONITORING OPERATIONS 1 1 6. 1 Adult Mosquito Monitoring 1 1 6. 2 Downstream Habitat Monitoring 1 1
7.0 CONCLUSION 1 2 7. 1 Present Mosquito Breeding 1 2 7. 2 Potential Mosquito Breeding 1 2 7. 3 Public Health Effects 1 2 7. 4 Measures to Avoid or Reduce Mosquito Breeding 1 2 7. 5 Mosquito Monitoring Programme 1 2
8. ACKNOWLEDGEM EN1S 1 2
MAPS 1 Mosquito Larval and Adult Sample Points - Damsite Area 1 3 27/2/90-7/3/90
2 Mosquito Larval and Adult Sample Points - External to Damsite 1 4 27/2/90-7/3/90
TABLES Larval Sample Results 1 5
2 Adult Mosquito Collections 28/2/90 and 1/3/90 1 7
APPENDIX / Photo 1 - Damsite looking downstream above adult trap 1 9 site (4) & (9) Photo 2 - Close up of a rock pool showing Anopheles larvae at 1 9 I a rv a I s amp I e poi n t ( 4) Photo 3 - General view of Erewe Thele, near adult trap site (8) 2 O Photo 4 - Downstream of damsite near adult trap site (10) 2 0 Photo 5 - Damsite in the bed of the Todd River at trap site (4) 2 1 Photo 6 - Upstream of Junction Waterhole near larval sample point (5) showing Typha reeds at margin 2 1 Photo 7 - Carbon dioxide baited EVS light trap below damsite at 2 2 adult trap (9) Photo 8 - Upstream of Wigley Waterhole at adult trap site (6) 2 2 Photo 9 - One of the Wigley Waterholes between adult trap 2 3 site (5) and (6) showing Typha reeds at RHS margin
I I Common Mosquitoes in the Northern Territory - Description 24 of Species, Habitats and Disease Potential
II I Mosquito Species Recorded from Alice Springs Area 30
IV Monthly Max. Numbers of Adult Female Mosquitoes per CO2 Trap-Night at Site "A", II Parpa Swamp, Alice Springs 1989 3 1 MEDICAL ENTCMOL03Y INVESTIGATION Q£ PROPOSED JUNCTION WATER .!::iQLE DNv1 Qbl THE TODD RIVER
MEDICAL ENTOMOLCXW BRANCH MARCH~
BACKGROUND
The Power and Water Authority is examining preliminary information for a possible flood mitigation dam at the Junction Water Hole on the Todd River near Alice Springs. An engineering consultant's report in May 1989 found no engineering factors precluding construction of a dam at the Junction Water Hole and suggested feasibility studies be undertaken, including environmental constraints.
Previous investigations for purely recreational lakes undertaken in the Alice Springs area included feasibility studies of Emily Creek in September 1985 and an environmental review for a dam on the Todd River in 1981. The latter report mentioned the possibility of an increase in mosquito borne arbovirus activity. The former report outlined the need to consider arboviruses and to prevent new mosquito habitats.
In January 1990 the Power and Water Authority approached the Department of Health and Community Services requesting a Medical Entomology investigation of the Junction Water Hole site to report on the present and potential biting insects and to assess the likely impact of a dam on insects of public health importance. The Medical Ent9mology Branch conducted a field investigation of the site from 27 February 1990 to 1 March 1990. This report outlines the results of the field examination and conclusions on the impact of a dam in respect to biting insects.
2.0 FIELD INVESTIGATIONS
2.1 Aim The aim of the investigation was to determine the species of mosquitoes present at the dam site and in the general vicinity, together with a measure of their abundance and their specific breeding sites. This information and other field observations would then be used to assess and report on the likely impact of the dam with regard to potential pest and public health problems posed by biting insects.
2.2 Surface Water Survey A surface water survey was carried out both upstream and downstream of the proposed dam site at Junction Water Hole to determine the present characteristics of any pools and the extent of surface water. Observations on the physical and biological characteristics were noted, including water depth, edge substrate, presence of vegetation, and the presence of relevant/aquatic life other than mosquito larvae. 2.3 Larval Samplinq Method The mosquito larval survey was conducted in the vicinity of the proposed dam site and a number of selected sites along the Todd River including Wiggleys Water Hole, the Telegraph Station and Heavitree Gap. Wiggleys Water Hole represents the more permanent natural pools in an undeveloped area receiving considerable recreation use , the Telegraph Station represents a sandy river bed receiving seepage and nutrients from a developed recreation area, while Heavitree Gap represents a sandy river bed receiving waste water via storm water drains from an urban environment.
Larval sampling was carried out with the aid of a standard larval dipper at selected or prospective habitats. A number of dips were taken at each site to determine the average number of larvae per dip and the growth stages (instars) of larvae present. Samples were only taken from pools representing the different habitats in one area. Larvae were collected alive and transferred to 70% alcohol at the end of each day. Selected samples were reared to adults. All larvae or reared adults were identified in the Medical Entomology laboratory in Darwin.
2.4 Adult Sampling Method Adult mosquito populations were sampled with dry ice (carbon dioxide) baited EVS light traps, which are standardized mosquito sampling devices widely used in Australia. Trap locations were chosen to sample populations near surface water habitats at the time of the survey. Traps were set at chest height before sundown and operated all night. Trap collection was between 7 and 8 am the following day. Traps were located as close to the river as possible and next to vegetation. All collections were sorted and identified on the day of collection, with reference samples taken for checking and inclusion into a reference insect collection at the Medical Entomology Branch in Darwin.
3.0 RESULTS
3.1 Surface Water Survey There were many pools in the bed of the Todd River from Erewe Thele to Heavitree Gap (See Map 1 ). Photos of the various habitats is shown as Appendix I.
The pools near Erewe Thele included relatively large deep pools with discrete sand or rock margins. The shallow downstream edge contained a few small cut off pools.
Between Erewe Thele and Junction Water Hole there is a 300 metre stretch of rock and sand pools with minor amounts of algae on rock surfaces below the water. A few pools had small stands of Typha reeds, but otherwise they were vegetation free and with relatively clear cool water. The lower portion of this section contained former rock pools that had dried up in the previous few weeks.
Junction Water Hole was a long, relatively deep sandy pool approximately two hundred metres in length. There were a number of shallow cut off sandy pools at the downstream end of the main pool, particularly along the eastern edge of the creek. Some pools were shaded by the steep sandy bank edged with couch grass with an over storey of tall ri v er red gums (Eucalyptus camaldulensis),
Downstream of Junction Water Hole there was a long dry sandy stretch of river bed while the section further down contained dry, former rock pools in a narrow braided section of the creek.
After the dry pools, there was a series of rock and sand pools beginning approximately 300m above the dam site. The upstream ones contained filamentous algae, some Cyperus reeds, and occasional Typha reed stands at the edges. The downstream pools, in the steep gorge area at the proposed dam site, were mainly deeper rock pools with steep sand or rock margins with little algae.
Below the dam site the river course was wide, with a dry sandy bed for at least 200m before becoming a series of rocky sand pools. The rock pools were more extensive in the recent past but had dried up in the upper section. The remaining pools in the downstream section contained no emergent vegetation and were relatively clear of filamentous algae. These pools became progressively larger towards the steep narrow gorge area which contained a series of relatively large rock pools.
Downstream of this gorge, the bed was relatively wide, dry and rocky for 200m. At the end of this section was a large deep relatively clear water pool, with a big stand of Typha reeds at the downstream end. This pool appeared to receive some recreation pressure, but less than the Wiggley Water Hole a little further downstream.
The Wiggley Water Hole pool had steep clay, sand, and rock sides with relatively deep water, with some small stands of Typha reeds just above the water line. There were a few isolated side pools at this pool. The water was relatively muddy and had a somewhat stagnant appearance. As it was at the end of an access road from the Stuart Highway, it probably received considerable visitor pressure.
The Wiggley Gorge, downstream from Wiggley Water Hole, consisted of relatively large narrow rock pools within the gorge area, particularly in the vicinity of the PAWA stream recording site .
Downstream of Wiggley Gorge, the river opened up to a dry, wide sandy bed .
Further downstream at the Telegraph Station, was a small marginal stream, on the eastern side of the wide sandy river bed, with dense stands of Typha reeds, papyrus reeds and steep banks lined with couch grass. The water was slowly flowing, with relatively high nutrient levels and abundant green filamentous algae. This water appears to originate from overwatering of lawns and other waste water from the Telegraph Station recreation area.
Other pools examined were much further downstream in Alice Springs itself near the vicinity of Heavitree Gap. These pools were very large and shallow with floating green/yellow algal mats and green filamentous algae. U Larval Sampling The results of the larval sampling are shown on Table 1. Only three species of larvae were recovered. Anopheles annulipes s.l. was the most abundant and was present in many of the small isolated rock or rock and sand pools in the bed of the Todd River from Erewe Thele to Heavitree Gap. The highest concentrations were in isolated sandy/rock pools without fish and with leaf litter or other organic matter. ~elatively high concentrations were found in pools with dense floating mats of green filamentous algae (Heavitree Gap and Telegraph Station), irrespective of the presence of fish. In pools with algae and fish or other aquatic predators, the larvae were closely associated with the algae, either on top of the semi-floating algae or in small spaces between mats of floating algae. An isolated sand pool with a high organic content (cow dung) had An. annulipes larvae of all instars throughout the pool and there were no aquatic beetles, fish or other predators present. Sand or rock pools with some algal growth in the bottom had occasional dragon fly and damsel fly nymphs, sometimes relatively high concentrations of mayfly larvae and often relatively high numbers of aquatic bugs of the family Corixidae (water boatmen). In pools with obvious aquatic predators, An. annulipes larvae were usually restricted to shallow sand edges. In pools that were relatively steep sided with sand or rock, larvae were usually absent or at very low densities In the larger pools with steeper or more distinct margins, larvae were only present in the shallow end of the pools either cut off from the main pool or almost so. Most of the larger pools and many of the smaller pools contained the native fish, Leiopotherapon unicolor (the spangled perch). The other two species, Q.ulax (Loph.) cylindricus and Q.ulax (Culex) species ~ were not common . .Qx cylindricus larvae were found in a cut off deep pool, shaded by the steep edge of the river bank at the end of a large pool at Junction Water Hole. There were no fish and few other aquatic predators in the pool and the water was slightly discoloured by tannins from leaf litter. The larvae were distributed throughout the pool and were all late instars suggestive of progeny from a single egg raft. A few other Qx. cylindricus larvae were present in a medium size sand pool at Junction Water Hole. This pool had leaf litter with a few water boatmen and the larvae were associated with many An. annulioes larvae and moderate numbers of QL ~ ~ larvae. There were no fish in the pool and the larvae were distributed throughout the pool. 3.3 Adult Sampling The results of the adult mosquito trap collections are shown in Table 2. There were only five species recorded, with An. annulipes being the most frequent. A description of three of the species and their health significance is shown as Appendix II. The highest numbers of ArL. annulipes in one trap (72) was in the vicinity of Heavitree Gap, reflecting the large area of breeding habitat in the vicinity. The presence of two males in the trap collection indicated a nearby source. Adult and larval sampling at the nearby II Parpa sewage ponds, indicated that the ponds were not a significant source of the mosquitoes collected in the Heavitree Gap trap. The next highest number of An . annulipes (26) was recorded at trap site 10, 500m downstream from the dam site. The relatively high catch at this site was probably due to the relatively large number of isolated rock pools nearby. Most other trap sites , despite the presence of larvae in nearby pools , showed relatively small numbers of An. annulipes. An. annulipes s.l.is known to be a species complex of at least seven species in Australia with morphologically similar larvae and adults. It is probable that the An. annulioes recovered represented two species, as the individuals could be separated into two groups based on either a 1/2 white proboscis or a black proboscis. Cx. annulirostris (the common banded mosquito), was only recovered from 'Heavitree Gap and the Telegraph Station, and then only in very small numbers. It is significant that these collections were near breeding sites receiving waste water from human activities. Cx, guinguefasciatus (the brown house mosquito) was only recovered from the Heavitree Gap site. This species usually breeds in waste water associated with human activity and the individuals recovered could have originated from the nearby sewage ponds, a septic tank, or a water filled container in _an urban environment. Cx. cylindricus males were recovered only from the Telegraph Station site. The males indicate that there is a nearby breeding site in the Todd River. This species is never numerous, does not bite humans and has no known public health significance . .G.& (Culex) ~ was the second most frequently recovered species, but only present in very low numbers. The collections at the sites along the Todd River indicate the presence of suitable breeding sites in isolated sand or rock pools. CL .5..Q. ~ is an undescribed species that is morphologically similar to ~ annulirostris. It has not been previously recorded from Alice Springs. It is not known to bite humans and has no known public health significance. 4.0 DISCUSSION 4.1 Present mosquito breeding habitats The surface water survey indicated considerable pools present in the Todd River bed, both upstream and downstream from the dam site (see photo record Appendix 11). The last rainfall, recorded from Bond Spring Station, was 32.8 mm on 10th, 11.5 mm on 12th, and 23.2 mm on 14th January 1990. The last rive r ;iC'N recorded before the present survey was on 12 January 1990 at the Wiggley WJternole Recording Station. Present surface water habitats are therefore the result of rainfall at least · 6 weeks previous. The area of surface water would have been much more extensive in the two weeks after rainfall than at the time of this survey. The number of mosquito species and the relative number of adults would have been higher for a few weeks after the last rain . Both would have been on the decline for at least two weeks before the present survey, as various pools dried up and other pools contracted. Mosquito species possibly present after rain would have included Aedes sapiens and Aedes eidsvoldensis. These species breed in freshly flooded temporary ground pools and arise from previously laid desiccation resistant eggs. All the larvae would have passed through their growth cycle at least 1 o days after flooding and the adults would have all disappeared by the time of this survey. Cx . annulirostris adults may have been present in the general vicinity of the dam site in the second or third week after rain but would have been in relatively low numbers due to the small extent of suitable breeding habitat available. The above species have disappeared as ground pools outside the bed of the Todd River dried up and the pools within the Todd bed became unsuitable due to receding water levels and an increase in fish and insect predator activity. The species list of mosquitoes found in the Alice Springs area is shown as Appendix Ill. Any of the species in addition to the ones mentioned above could be found in the vicinity of the dam. The principal species and an indication of their relative abundance over a twelve month period is shown as Appendix IV. If major breeding sites result from dam construction , the same species would be potential problems and similar seasonal abundance would be expected. The present mosquito breeding habitats are not highly productive due to the low level of nutrients, the contraction of the pools and the concentration of predators such as fish, aquatic beetles, mayfly, dragon fly, and damsel fly nymphs, and the relative openness of the remaining pools. Most pools presently contain little surface algae, emergent grass or reeds and with their discrete margins offer little opportunity for larvae to escape from predators. - An. annulipes larvae were the most frequent because of their ability to escape predators by remaining in very shallow water at the extreme edges of pools and by their ability to shelter among floating algae or other debris. An, annulipes can exploit the larger pools as well as the smaller pools with or without fish. At present the Culex species are only exploiting the smaller isolated pools, particularly those without fish . The isolated pools with relatively high numbers of aquatic beetles are not suitable habitats for Culex as these insect predators can easily locate any larvae present. The other habitats at the Telegraph Station and Heavitree Gap are much more productive because of the greater amounts of green filamentous algae and other vegetation in the water affording much more shelter from aquatic predators. These habitats also have a stable water level and relatively high nutrient levels which together favour higher populations of larvae. 4.2 Potential Mosquito Breeding Habitats During and immediately after dam construction there will be an increasing body of water impounded behind the dam wall. This rising water surface will progressively flood all the previous isolated pools, particularly those near the dam wall, upstream of Junction Waterhole and near Erewe Thele (see Map 1 ). A single body of water will permit fish to have access to most parts of the water body. These fish, together with wave action, will prevent most mosquito breeding in all parts of the impoundment except in the more sheltered pockets. However as the water level rises, there will be an accumulation of flotsam at certain margins made up from grass, leaves and twigs. This flotsam will dampen wave action and allow protection from fish and other aquatic predators. These sheltered habitats would be rapidly exploited particularly by An. annulipes,and to a lesser extent Q..L, annulirostris 'before aquatic predators could increase in numbers. This would lead to elevated levels of adults until the predators increase in numbers. As aquatic predators increase, the numbers of mosquito larvae would decrease until a balance was achieved. After the impoundment fill there will be breakdown of flotsam and submerged vegetation, leading to elevated levels of nutrients. This elevated level of nutrients will lend to higher levels of microorganisms which will provide ample food for mosquito larvae and other aquatic organisms. As mentioned previously, this can lead to a temporary increase in mosquito larvae until predator numbers achieve some balance. However if the nutrient level is high enough, this could lead to significant amount of floating algae or increased weed and reed growth in certain areas, giving rise to a continuing and elevated level of mosquito numbers. Certainly if flotsam in sheltered areas remains to prevent predator activity it could lead to relative high levels of An, annulipes and .Gk annuljrostis. If the high level of nutrients does result in considerable algae growth and floating algal mats these algal mats could persist for a considerable time. Algal scum has already formed in some of the isolated pools in the relatively low nutrient level water in the bed of the Todd River and could only increase with the breakdown of drowned vegetation. If this algae accumulates in the more sheltered edges, it would provide suitable breeding sites for An. annulipes and to a lesser extent Cx. annulirostris, .Q£ cylindricus and ~. species~- An. annulipes would be able to exploit any new edge habitat better than most other species, as it lacks a siphon and can thus exist in very shallow water. It could however not persist at margins with any appreciable wave action. Cx. annulirostris is only likely to exploit the more sheltered areas with higher levels of debris and flotsam as would occur in the arms of the impoundment and only if nutrient levels were relatively high. There is little likelihood of Aedes species habitats within the impoundment because with a temporary decrease in the water level the relatively free draining and steep nature of the impoundment, margins will provide very few edge pools suitable as Aedes breeding habitats. During the period of dam filling there is likely to be an effect on the downstream mosquito habitats at least from below the dam wall to the Wiggley Gorge. If there is no overflow from the dam for a considerable period there is likely to be an artificial drying up of the more perennial pools. This initial drying would concentrate the fish and aquatic predators and hence these habitats would be even less favourable for mosquito breeding. However if these pools dry up completely and are subsequently partially filled by rain, without sufficient river flow to allow fish migration from more perennial pools, the absence of fish and relatively low numbers of aquatic insects would result in high levels of mosquito breeding. This absence would particularly favour Q.& annulirostis, as well as ~ annulipes. This effect may not occur if the native fish can persist in the bed of the Todd River in isolated pools or can persist in the mud. The spangled perch is reported to be capable of aestivating in the mud but this would need verification under those hc;.bitat conditions currently existing in the Todd River. In the longer term, with good management practice and a stable and relatively low nutrient status. there is likely to be little floating algal mats and low levels of flotsam and debris around the lake margin. Gentle wave action at the relatively steep shore line and the gradually descending water level after rain episodes is not likely to lead to any significant areas of macrophyte growth and hence there will be little favourable habitats for mosquitoes around the majority of the lake shore. There is however a possibility that siltation , extended stream flow and higher water tables in the upper reaches of the main stream bed of the Todd River and 1he upper reaches of the Colyer Creek and to a lesser extent Junction Creek could lead to some areas of pooling, shallow water and macrophyte growth. This possibility would be increased if there are any significant tourist or industry developments in the upper reaches of these creeks which could lead to extended stream input or add waste water and nutrients into the system. This would offer favourable habitats for An. annulipes, and Cx . annulirostris. The development of these habitats would be significant under increased rainfall patterns. The most likely location of significant mosquito breeding would be in the bed of the Todd River below the dam wall. If the dam leaks fo any significant degree, the area of sandy river bed below the dam could become a permanent aquatic habitat, with Typha and papyrus reed growth similar to that which exists near the Telegraph Station. The extent of such an area would depend on the degree of dam leakage. The area could vary from a relatively small pool with some mosquito breeding to a river wide expanse of thick reed growth with significant areas of habitat suitable for An. annulipes, .Q.L species~ • .G.L cylindricus, and CL. annulirostris. With significant leakage, the increased and prolonged flow of water could maintain pools from the dam wall downstream to Wiggley Gorge for a lot longer than presently occurs. This would lead to greatly increased Typha reed growth in the bed of the Todd River, impedance of fish predation, and significant increases in mosquito numbers. An example of this type of habitat can be seen now in the bed of the Todd River near the Telegraph Station. If there is no leakage in the dam, and the pools below the dam dry up completely on a regular basis , there is a possibility of ephemeral mosquito breeding habitats without fish predators after rain. This would lead to increased number of at least An. annulipes and possibly .G.L annulirostris for relatively short periods, depending on rainfall. This problem would be decreased if the dam overflow structure enabled fish survival over the overflow and there was fish re-colonisation of below dam habitats. If the green house scenario predictions are accurate, and there is a 50% increase in rainfall in Central Australia by the year 2030, the downstream habitats are not likely to dry up, and both the downstream habitats and the habitats in the upper reaches of the main contributing creeks to the dam are likely to have significant macrophyte growth and significantly more mosquito breeding. 4.3 Potential Public Health Problems Posed by Biting Insects The principal potential public health proplem posed by increased mosquito breeding in the Todd River associated with dam construction is the possible increase in arbovirus diseases such as epidemic polyarthritis and to a lesser extent Australian Encephalitis. 4.3.1 Epidemic Polyarthritis Epidemic polyarthritis is a relatively rare disease in Alice Springs, with laboratory confirmed cases rarely more than 1 per year. This is despite extremely high numbers of the main potential vector Cx, annulirostrjs, in the vicinity of II Parpa Swamp. Because of topography and wind direction, the mosquitoes originating from II Parpa rarely affect the residential areas of Alice Springs north of Heavitree Gap. There are still recreation and residential areas south of Heavitree Gap that offer appreciable possibility for human/mosquito contact. The absence of laboratory confirmed cases may obscure the number of clinical cases of this disease, although even then it is unlikely that epidemic polyarthritis is currently a significant disease in Alice Springs. The absence of this disease may be due to an absence of the virus or relative low numbers of marsupial reservoirs rather than vector parameters. The amount of Q.L annulirostis breeding associated with the dam is likely to be significantly less than currently exists at II-;- Parpa Swamp. The degree of human/vector contact in a day recreation area of the dam, if permitted, is also likely to be less than that in the current residential/recreation areas south of Heavitree Gap. If usage at the lake is mainly day usage and upstream of the dam wall, and away from the upper reaches of the contributing creeks, it is very unlikely that there will be any significant increase in this disease after dam construction and if the recommended measures mentioned in a later section are implemented. The possibility of at least some cases of epidemic polyarthritis would increase if there were camping accommodation areas below the dam wall together with significant mosquito breeding habitats created below the dam wall. However a caravan park is presently situated near Heavitree Gap and there is currently little evidence of disease in this area. One possibility is that the new dam would create new or more suitable habitats for marsupials and provide a more favourable environment for epidemic polyarthritis transmission than currently exists in II Parpa Swamp. There is no information readily available that could clarify this possibility, and until such information does become available, the best precaution is to ensure any additional mosquito breeding is kept to a minimum. Australian Encephalitis This disease is a very rare occurrence in Alice Springs with the last cases recorded in the 1974 Australia wide epidemic. The main vector in the Alice Springs area is likely to be QL annuliostris. The main host of this virus is thought to be water birds. The new dam will not be as favourable to water birds as II Parpa currently is and thus II Parpa would pose a much greater threat to human health than the present dam. During an epidemic an area such as the dam may provide an added possibility for human/vector contact, but this increase is not likely to be significant particularly as vector numbers could be kept to a minimum. Dam construction with recommended safeguards is not likely to lead to any great threat from this disease than currently exists in the vicinity of Alice Springs. Malaria Alice Springs is not regarded as being within the receptive area for malaria transmission in Australia. This is due to a combination of the absence of certain vectors, vector numbers, longevity of the vector and environmental conditions. Although some of these factors could change with the green house scenario, it is not likely that the dam construction would lead to any appreciable change in most of these factors and thus there should not be any significant increase in malaria receptivity. Nuisance Insects It is possible that Chironomid midges, a group of non-biting midges, could find favourable habitats in or downstream from the new dam. However, the potential for Chironomid midge productivity would be relatively insignificant compared with the numbers produced by the II Parpa sewage ponds and II Parpa Swamp. Chironomid midges could prove a localized nuisance by being attracted to lights at night during the first few years after dam construction, but as nutrient levels decrease with the breakdown of submerged vegetation, any Chironomid problem should stabilize to a level significantly less than already exists in the vicinity of the residential areas south of Heavitree Gap. There is a possibility of additional Black fly (Simulidae) breeding being created by providing running water over rock habitats. Blackflies are a group of flies which contain blood sucking species, but are not known to cause human disease in Australia. Their habitat would not occur to any significant degree immediately downstream of the dam wall due the sandy nature of the bed of the Todd River. Suitable habitat could occur in an overflow structure or further downstream in the rock gorge area and then only be a significant possibility if there was considerable dam leakage. Otherwise blackflies would not be much greater problem than currently exists. 5.0 MEASURES TO REDUCE OR AVOID MOSQUITO BREEDING 5.1 Design Features 5.1.1 Fish transfer An engineering feature to allow fish to' transfer both from downstream into the lake and from the lake to the downstream habitats should be considered. This could take the form of a fish ladder in the overflow channel. Such a design feature will alleviate the need to consistently check the downstream habitats for the presence of fish and the need to manually restock these downstream habitats. 5.1.2 Stock Exclusion. There is a need to fence the dam area, at least to the normal capacity level, in order to prevent stock footprints and disturbed areas in the creeks leading into the lake. Such disturbances at the margins lead to isolated cut off pools capable of· providing mosquito breeding sites. In addition, dead stock or animal wastes in pools could provide localised high nutrient habitats that would be suitable for prolific mosquito breeding. The Siting of Public Access Areas The siting of public areas should consider the potential to allow nutrient rich water to enter the lake. Public access areas that are landscaped and watered will certainly lead to nutrient run off or prolonged seepage of nutrient rich water, with similar habitat consequences to that which currently exists at the Telegraph Station site. If public access areas are to be near the lake margin, they should be near the steep wave actioned margins, rather than in a sheltered relatively narrow arm. This would reduce the potential for stable higher nutrient habitats to develop. A public facility with septic tanks and landscape developments near the Stuart Highway on Colyer Creek has a greater potential to develop mosquito habitats in the Colyer Creek arm than similar facilities at the margin near the dam wall. Any septic tanks or other potential waste water sources should be sited well back from the lake margin and have a waste water disposal mechanism to prevent nutrient rich water to reach the lake. Any such facilities immediately downstream of the dam wall would have an even greater potential to develop mosquito habitats. 5.1.4 Water Level Manipulation A mechanism should be included in the design to allow the water levels of the lake to be manipulated to periodically strand flotsam or to facilitate the removal of weeds or other unwanted vegetation. 5.1.5 Sediment Traps If any shallow semi-aquatic reed habitats develop within the lake, they are most likely to occur in the upper regions of the arms at the normal water retention level. Silt loads would be deposited into these areas and the extent of this habitat would become more extensive. To prevent potential mosquito habitat, it would be better to site silt traps in the arms of the creeks above the normal water retention level. The indicated possible silt trap site on the Todd River is below normal retention water level and thus would pose a potential problem. In addition, silt traps need design features to allow them to drain and to be periodically maintained. 5.1.6 Prevention of Leakage The greatest potential for additional mosquito breeding habitats will occur by dam leakage. If leakage is considerable, permanent shallow Typha reed pools will occur below the dam wall. Design features should be incorporated to reduce such leakage to a greater extent than would be necessary from just engineering parameters only. If there is any reasonable expectations for dam leakage to occur, potential mosquito habitats should be prevented or reduced by having the leakage collected into a formalised relatively deep (1.5 metres or greater) pool below the dam wall. If there is likely to be any consistent overflow out of such a pool, the excess water should be removed by pumping or otherwise dispersed. 5.2 During Construction 5.2.1 Vegetation Removal All vegetation in the inundated area below normal retention levels should be removed to reduce the amount of organic material within the lake. This would include clear felling and removal or burning of all trees, bushes and any other vegetation. 5.2.2 Flotsam Removal As the lake is filling, there should be a regular program of flotsam collection and removal. Such removal would be facilitated by stranding flotsam with water level manipulation . 5.2.3 Mosquito Monitoring As the lake fills, the impoundment and the present pools below the dam should be regularly monitored for the presence of mosquito larvae and their aquatic predators. If mosquito numbers proliferate within the impoundment, timely mosquito control operations could then be carried out. Larval control should consider the scope of increasing natural biological control before chemical control methods are considered. One such method would involve the restocking of the lake with endemic fish if fish. 5.3 After Construction 5.3.1 Prevention of Nutrient Input Nutrients could result from developed areas or other sources such as development of commercial enterprises within the catchment. Any development proposals such as intensive animal holding areas, abattoirs or tourist facilities within the catchment should be carefully examined before approval to ensure that waste water from these establishments is not allowed to contaminate the lake and its tributaries. 5.3.2 Weed Control Various aquatic or semi aquatic weeds could colonise the lake margins. Those that have the greatest capacity to create favourable mosquito habitats include Typha species, Papyrus species and Couch grass. Any areas of these species should be periodically removed by a regular weed inspection and control programme. 5.3.3 Flotsam Removal As already indicated, any flotsam accumulation, particularly in the upper arms of the creeks leading into the lakes should be periodically removed. This would be best achieved by stranding the flotsam and physical removal or burning. 5.3.4 Mosquito Control If any mosquito control is required, formulations involving B.t.i. (Bacillus thurinaiensis var. israelensis) should be considered before any other formulation. Under certain circumstances a granule application of insecticide may be required. At this stage only Temephos 1% sand granules are recommended for mosquito control requiring granule application. 6.0 Monitoring Operations 6.1 Adult Mosquito Monitoring It is necessary to monitor adult mosquito numbers for at least a 12 month period before dam construction to determine base line mosquito information. A minimum requirement would be for 3 carbon dioxide baited mosquito traps to be set every 2 months. The trap locations should include one site below the dam wall, one at the proposed lake margins near trap site 8 and one in the upper margin in Colyer Creek at the expected normal retention level. Such data could then be compared with monitoring results after dam construction to determine whether there has been any increase in mosquito species presence or abundance. If any such changes occur, mosquito larval surveys should be carried out in the above dam habitats. Such a monitoring operation could be a joint programme between the Department of Transport & Works and the Department of Health and Community Services. 6.2 Downstream Habitat Monitoring Downstream habitats should be monitored for mosquito larvae, their aquatic predators, and semi aquatic vegetation: Monitoring should be carried out at least a few times a year before construction over ·a 12 months period and a few times in the first and second years after construction , to determine if any ecological or habitat changes occur. I ~-..;> I '\D 7.0 CONCLUSION 7.1 Present Mosquito Breeding There are only a limited number and a relatively low abundance of mosquitoes in the vicinity of the Junction Waterhole dam site. They are presently not in pest numbers and potential disease vectors are at very low levels. 7.2 Potential Mosquito Breeding Potential mosquito breeding sites during or after dam construction include the present downstream pools, the impounded water during filling of the lake, the sheltered arms of the creeks after filling, and the below dam habitats if leakage occurs. The margins of the lake will be relatively steep and rocky. With a consistently decreasing water level and periodic reflooding, sizeable and stable mosquito habitats are not likely to develop around the majority of the la.ke margin. 7.3 Public Health Effects If the recommendations to prevent additional mosquito breeding are heeded, there is little likelihood of any increase in mosquito borne disease in the vicinity of the proposed dam. 7.4 Measures To Avoid or Reduce Mosquito Breeding If there is only minimal dam leakage and the recommendations to avoid or prevent mosquito breeding are incorporated into the design and management of the dam, there is likely to be a minimal increase in mosquito numbers as a result of dam construction. 7.5 Mosquito Monitoring Programme There is a need to begin both adult and larval mosquito monitoring programmes as soon as possible to determine base line levels of mosquito species and abundance to enable later comparisons to be carried out. Acknowledgements Apart from the assistance of various members of the Medical Entomology Branch, the assistance of Mr Richard Marks, Strategic Planning, Darwin; Mr John Childs Senior Engineer and the field assistance by Ms Kym Christifeli and Mr Noel Gibbons, all of the Power and Water Authority, Alice Springs, is gratefully acknowledged. Access to the study sites was kindly assisted by Ms Tanya Heaslip of the Bond Springs Pastoral Company. The native fish was kindly identified by Mr Rex Williams of the Museums and Arts Gallery of the Northern Territory. PETER WHELAN Senior Medical Entomologist ~- 1.4--_.:> 1-/ CAi"CHMENT BOUNDARY ;· .J ,~Y .. ~ .. · ) ROAD .. /· "> <:/)_,_) ~ c;..: ~/ ~ .J. JUNCTION WATERHOLE DAMSITE ,._-~-- ~APH STATION \6NDDDL YA RO~D Springs Hee Yltree Gap km 5 O 5 10 15 km =---- ! LEGEND @ ADULT MOSQUITO TRAP SITE 9 LARVAL SAMPLE POINT MAP 1 a MOSQUITO LARVAL AND ADULT SAMPLE POINTS - DAMSITE AREA 27/2 / 90 7/3/90 - 0 0 ::!00 L::G;ND PROBABL! 1..u .. ~JMUM i::-1_:,oo L:V:!.. - TOP OF :MBANKM:Ni ::.:... 57'0 APPR::X. ,co Y:AR ;::-1-:,00 L~V:!.. ::.:... ee5 .·. • . ··~·:-:.:- : .·. .. BED OF RIV:R .. . • AOUL~ MCSCU(70 ":"R.AP sr~:: 0 :..ARVAL SAMP'....= P'.)IN7 --- '....ARG~ Poc:..s DURING SURV!:Y AREA OF SMAL:...=rl Poo:..s DURING SURV:Y MAP 2 • MOSQUITO LARVAL AND ADULT SAMPLE POINTS EXTERNAL TO DAMSITE 27 /2/90 · 7 /3/90 TABLE 1 JUNCTION WATERHOLE DAMSITE MOSQUITO INVESTIGATION LARVAL SAMPLE RESULTS SPECIES SAMPLE LCCATlQ\J DESCRIPTION AVERAGE NUMBER PER DIP SITE No. (SEE MAP) Anopheles Culex Culex annulipes cylindricus species 92 (Larval (Larval (Larval staaes) staaes) staqes) 1 - 2 k3 - 4 p 1 -2 3-4 p 1 - 2 3-4 p 1(a) Phyllis Ck ! Small sandy cut-off road ! Waterhole with aquatic bugs and leaf 1 0 , 0 2 - - - - - ! - litter, sunlit. Larvae continuous I 1(b) Ditto Small isolated shaded pool with, low dung and 25 20 2 - - - - - I - discoloured larvae ! l throuahout water t 1(c) Ditto Small shallow cut-off pool I shaded with leaf litter, - 1 2 - - - l - larvae throuahout I ! 1(d) Ditto Cut-off pool (1 m2 ) with a i few aquatic bugs and leaf 20 1 5 2 - 1 - 1 3 - litter through the pool, sunlit larvae. I 2(a) 400m Shallow pool with many ! I downstream fly larvae and aquatic 1 1 ------of Phyllis Ck bugs, sunlit, rock and Waterhole sand. 2(b) Ditto Small 100mm deep rock ! and sand pool with fish and ------no veoetation. I 3(a) i 600m down- Large 200mm deep rock l stream of and sand pool with fish. ------! . Phyllis Ck i Waterhole, I I upstream of I damsite I 3(b) Ditto Small shallow cut-off sand i . I pool with aquatic bugs, 1 0 1 0 1 . - 2 1 - - fish and dragonfly larvae. I Larvae at edge with green I alaae. ! 4 400m up- Medium sized shallow i l stream of sandy rock pool with 1 ------I - Phyllis Ck Typha reeds and fish. I I Waterhole ! 5(a) 500m up- Small shallow rock and ! stream of sand pool with aquatic 2 . - . - - - - I - Phyllis Ck l bugs(Corixidae) and fish, I Waterhole larvae at edae onlv. l 11/12/90 TABLE 1 SPECIES SAMPLE LCCATICN DESCRIPTION AVERAGE NUMBER PER DIP SITE No. (SEE MAP) Anophe~es Culex Cule1 annulipes cylindricus species ( Larval (Larval ( Larn staaes) staoes) staaes , - 2 3-4 p , - 2 3-4 p 1 - 2 3 -41 5(b) Ditto Small 1 50mm deep rock pool with no fish, larvae - 1 - - - - 5 5 continuous. I 5(c) Ditto Small shallow with green filamentous algae and fish. 2 1 - - - - - · I Larvae at edae. S(d) Ditto Large deep rock pool with fish and filamentous algae. 1 1 - - - - - Larvae restricted to algae at edae. 6 600m up- Small shallow rock. pool stream of with mayfly, damselfly ------Phyllis Ck larvae and aquatic bugs. Waterhole ?(a) Erewe Thele Large deep sandy pool with (Junction rocks and fish. ------Waterhole) I · 7(b) Ditto Small cut-off sandy hoofprint with clear water ------at edae of biq pool. 8 Wigleys Typha reeds, deep large . Waterhole rock. and sand pool with 1 1 - - - - - fish. Polluted water, larvae edae onlv. 9 Telegraph Green filamentous algal ! Station pools with fish, yabbie, 20 1 0 2 - - - 1 1 mayfly, damselfly and dragonfly nymphs. Running water. Larvae only at edge or associated with alaae. I 1 0 Heavitree Gap Large sheet of algae in : pools with fish. Larvae 5 5 2 - - - - closely associated with alaae. TABLE 2. JUNCTION WATER-HOLE MOSQUITO INVESTIGATION ADULT MOSQUITO COLLECTIONS 28/2/90 AND 1/3/90 Number of female mosquitoes collected in EVS CO2 traps (males bracketed) Species TRAP TRAP N:J. LCCAllQ\J An. ann. Cx.ann Cx.quin Cx.cvl Cx.92 TOTAL 1. Colyer Ck 4 4 Stuart Hwy 2. Junction waterhole Todd River 3. 500m upstream of Junction waterhole 4. Junction 2 waterhole dam site - riverbed 5. Wiggleys 4 4 waterhole, west side of Todd River 6. 500m upstream 6 2 8 of Wiggleys waterhole 7. Heavitree Gap Motel 7 2 ( 2) 4 77 ( 2) river bank 8. 1km upstream 2 ( 1 ) 3 ( 1 ) from Junction waterhole at Erewe Thele V 9. Junction waterhole 2 3 just down stream of dam site. 10. 500m down stream of 26 26 dam site - Rocky gorge. 11 . Telegraph Station 2 ( 1 ) 2 5 4 ( 6) Reed/water at bank. ------1 20( 4) 3 4 5 6 133(9) COMMON MOSQUITOES IN THE NORTHERN TERRITORY DESCRIPTION OF SPECIES, HABITATS AND DISEASE POTENTIAL PETER WHELAN SENIOR MEDICAL ENTOMOLOGIST and WENDY KELTON TECHNICAL OFFICER MEDICAL ENTOMOLOGY BRANCH N. T. DEPARTMENT OF HEALTH AND COMMUNITY SERVICES COMMON MOSQUITOES IN THE NORTHERN JERRITORY DESCRIPTION OF SPECIES, HABITATS AND DISEASE POTENTIAL INTRODUCTION: Mosquitoes are small, slender bodied, two winged flies belonging to the family Culicidae. They differ from all other flies in having a prominent proboscis or feeding tube projecting from the front of the head. A pair of sensory palps flank the proboscis on either side. In Anopheles species the palps are as long as the proboscis, but in the females of most other species the palps are considerably shorter. The palps of the male mosquito are usually as long as the proboscis and are often more hairy and sometimes ornate. The males also have more bushy antennae when compared with the sparse antennae of the female. The body and wings of mosquitoes are clothed in scales. Colour, si2e, shape, and arrangement of the scales are used to identify the different species of mosquitoes. In the Northern Territory there are approximately 100 different species of mosquitoes. Of these only about 40 species are known to bite people, and only about 20 species occur in numbers large enough to cause pest problems. The mosquitoes which are known to occur in the Northern Territory are listed in Appendix I. Both the male and female mosquitoes feed on plant nectar, but the female also requires a blood meal to supply sufficient protein for egg development. Mosquitoes show considerable variation in their preference for hosts, with some species feeding selectively on cattle, horses, marsupials or man. Some species are fastidious about the source of their blood meal. For example Uranotaenia feed on reptiles and frogs, and Aedeomyia preferentially feed on birds. Other species, such as Culex annulirostris will generally feed on whate v er source of blood is available. The time of feeding varies for different species . Many mosquitoes feed just after sundown. Others prefer later in the night, and some will bite preferentially in the early morning. Some species of Aedes mosquitoes will bite at any time during the day or evening. The place of feeding also varies, with some species flying far in search of a blood meal, while others remain very close to the breeding site. Some species will enter buildings in search of a host, others will only bite outdoors . After feeding, the female chooses a suitable resting place, usually cool and humid , where the blood meal can be digested and egg development can proceed. A time lapse of two to three days usually occurs from blood meal to egg laying. Mosquitoes . have four distinct stages in their life history - egg, larva ( or wriggler), pupa ( or tumbler) and adult. The larval and pupal stages occur only in water, while the adult is an active flying insect . 2 Eggs are laid singly on the water surface by Anopheles mosquitoes, •in rafts on the water surface by Culex mosquitoes, and singly on moist surfaces above the water level by Aedes mosquitoes. Aedes eggs can withstand drying out for many months without ill effect, and will hatch when the water level rises and the eggs are flooded. The larvae emerge from the eggs and live in the water through four growth stages. The skin is moulted between each growth stage as the larva increases in size and complexity. Host larvae feed by drawing water into their mouths by means .of fan shaped mouth brushes on the front of the head. Particles of food are drawn in with the water. Some species of larvae are predaceous on other larvae and have modified mouth brushes for capturing and holding their prey. Most species of mosquitoes have larvae which come to the surface of the water to breathe. Host larvae have a siphon, which carries the breathing tubes, on the last segment of the abdomen. They obtain air by hanging suspended by the siphon from the water surface . Anopheles mosquitoes do not have a siphon, but instead have breathing tubes on the surface of the last segment of the abdomen, and lie flat at the water surface to breathe. Some species with very short siphons may be mistaken for Anopheles at first glance. Some genera, such as Hansonia and Coquillettidia, obtain air from submerged aquatic or semi-aquatic plants. They have a specially modified tip on the siphon with which they can pierce the air chambers in submerged stems or roots of plants. These species have no need to regularly come to the water surface. At the conclusion of the last larval growth stage, the skin is shed and the pupa emerges. The pupa is a non -feeding stage, during which the adult form develops within the pupal skin. When the adult has developed, the pupal skin splits along the dorsal surface, and the adult emerges onto the surface of the water. The pupal stage usually lasts from one to two days. The time taken from egg to adult varies, depending initially upon the species concerned , but secondly on temperature, food availability and extent of crowding. In the Northern Territory 10 to 14 days would be sufficient time for most species to mature, but for species in temporary situations such as tidal pools, or ephemeral flooded areas further inland, the period is shortened to about 5 - 6 days. Typical coastal mosquito breeding situations are depicted in Appendix II. The following text describes some of the more common and important mosquitoes occurring in the Northern Territory, with some detail of biology, adult habits, distribution and association with disease. UV IL-::::::, /1..- () 5 Anopheles a nnulipes "The common Australian Anopheline" Description of female: This is a species complex with more than 5 species, of which probably at least two species occur in the Northern Territory. A speckled grey mosquito with extensively spotted wings . The palps are as long as the proboscis . Three wide white bands on the apical half of the palps are separated by two narrow black bands. The proboscis is usually pale scaled on the apical half in northern specimens. The southern specimens may have only slightly paler scaling on the apical half of proboscis. Both the top and bottom of the abdomen are dark except for a few white scales near the apex. Description of larvae: The larvae are very variable in colour. They have no siphon. The head is as long as it is broad. The inner clypeal h~irs on the front of the head are wide apart, and the outer clypeals are branched. This species can be similar in appearance to A.!L.... meraukensis in respect of the outer clypeal hairs, but can be differentiated by the air scoop on the last abdominal segment. In A.!L.... annulipes the median plate of the scoop is broad and has no lateral projections. Breeding Places: An. annulipes can breed in all kinds of temporary and permanent ground pools, stream and swamp edges, and amongst floating weeds in vegetation away from banks of streams and swamps. Also occurs in rock pools and large open containers such as drums and disused swimming pools, and sometimes found in slightly brackish water. Adult Habits: Like all Anopheles species, it stands on its head to bite. Bites by night, particularly at dusk and dawn, and will enter houses. It bites man readily but will also feed on cattle. Resting places are in hollow stumps, drums, banks of streams and stormwater pipes. This species is abundant in the Northern Territory from February to April, although never very numerous in coastal situations. The flight range is approximately 2km from the breeding areas. Distribution: Papua New Guinea and throughout Australia, including Tasmania. An. annulipes s. 1. occurs throughout the Northern Territory. Larvae have been found in the Darwin area in Leanyer Swamp, Ludmilla, Marrara Swamp, Botanical Gardens, and the Sandy Creek complex at Casuarina. Common at the edges of Nhulunbuy Lagoon, and Il Parpa Swamp in Alice Springs. Disease potential: Capable of carrying malaria, and is a suspected vector in the Northern Territory. <....J V IL-"::;) IL ( 1 3 Culex a nnulirostris "Common banded mosquito" Description of female: A medium sized, brown mosquito with a square tipped abdomen and a white band around the middle third of the proboscis. The legs have mottled femora, and the tarsi of the hind legs have narrow white basal bands . The segments on top of the abdomen have basal white bands produced into a point in the middle, while the underside of the abdomen has black transverse bands interrupted in the middle by white scales. Description of larvae: Larvae are pale with a relatively long siphon with 6 groups o f hairs along each side of the siphon. The antennae on the head have the bottom 2/3 white and the tip dark. The anal papillae are pointed, and transparently pale. Breeding Places: Natural freshwater swamps, lagoons, pools, and streams associated with vegetation, but Culex annulirostris will also breed in many artificial situations such as stormwater drains, grassy edges of sewerage ponds, and disused swimming pools. They may breed in plague numbers in low lying grassy areas where the water lays for 2-3 weeks. It has been found in brackish water in salt marshes, although is not usually found in areas exceeding one third salt water. This species may breed in large numbers in the dry season in grassy sewerage lagoons and stormwater drains. Adult Habits: Cul ex annulirostris bites people, birds and other animals, mainly at night. It is the chief non domestic pest in Australia and the most common mosquito biting in the Northern Territor y. It can fly from 4 to 10 kms from its breeding place. Di stri buti on: Papua New Guinea, South Pacific, Indonesia and the Phillipines, and throughout Australia. It is the most common mosquito in the Northern Territory, particularly where there is inadequate disposal of waste water. Around Darwin, Culex annulirostris occurs in large numbers in the wet season and early dry season in Leanyer Swamp, Marrara Swamp and Coconut Grove Swamp. Commonly in high numbers around Nhulunbuy Lagoon, Jabiru, Il Parpa Swamp area in Alice Springs, and throughout the wetlands along the Northern Territory coast. Disease potential: Culex annulirostris is the confirmed vector of Murray Valley encephalitis ( MVE) virus in Australia, and is capable of carrying Ross River virus , Kunjin virus and other viruses. It can transmit heartworm of dogs. In West Irian, it is capable of carrying filariasis . 1 4 Cul ex a uinquefasciatus "The brown house mosquito" Description of female: A light brown mosquito with a square tipped abdomen. Tarsi of hind legs are all dark, with no white bands. There are curved white transverse bands on top of the abdomen at the base of each segment. Pale underneath the abdomen, sometimes with scattering of dark scales in the centre of each abdominal segment. Proboscis all dark on top, and usually with some pale scaling basally underneath. Palps much shorter than proboscis. Description of larvae: Culex quinguefasciatus is a grey brown larvae with a light brown head and siphon. The antennae are a uniform grey colour. The siphon is of medium length with a characteristic bottle shape, and has 3-4 paired groups of ventral hairs and one pair of lateral hairs. Breeding Places: Polluted water close to human habitation. A very important source of large numbers of this species are unsealed septic tanks and primary sewage ponds . Other sources are polluted ground pools, storm water drains, sumps, gully traps and any artificial containers holding water such as tins, tyres, drums, and disused swimming pools . Adult Habits : Bites mainly at night, and is frequently the cause of complaints in domestic situations in the Northern Territory. It will feed readily on poultry when available and commonly bites dogs. Culex quinquefasciatus is the mosquito most commonly found inside houses , and it will remain inside houses to digest a blood meal. It will harbour in dark humid areas like cupboards, underneath sinks and near toilets and baths . This species travels from 1 to 2 km from the breeding place . It bites mainly at night, and stands with the body horizontal to skin. The wings make an annoying buzzing sound that is frequently heard as it approaches. Distribution: Worldwide in tropics and subtropics. Found throughout the Northern Territory wherever sites are available . Disease potential : It is capable of carrying heart worm of dogs. Culex quinguefasciatus has been shown in laboratory trials to be a poor vector of Murray Valley Encephalitis virus . In other countries it is a vector of filariasis . APPENDIX III MOSQUITO SPECIES RECORDED FROM ALICE SPRINGS AREA MEDICAL ENTOMOLOGY BRANCH NORTHERN TERRITORY DEPARTMENT OF HEALTH & COMMUNITY SERVICES SPECIES COLLECTION METHOD L/T M/B R L An. (Cel) amictus X X X An. (Cel) annulipes X X X Ae. (Fin) alboannulatus X Ae. (Fin) notoscriptus X X Ae. (Mac) tremulus X X X Ae. (Mac) species 125 X Ae. (Muc) alternans X X X Ae. (Och) eidsvoldensis X X Ae. (Och) pseudonormanensis X Ae (Och) vigilax X X X Ae. (Och) vittiger X X Ae (Och) species 71 X X Ae. (Och) species 85 X X Ae. (Och) sapiens X X Ae. (Psk) bancroftianus X Cx. (Cux) annulirostris X X X ex. (Cux) australicus X X X ex. (Cux) quinquefasciatus X X X ex. (Cux) species 92 X X Cs. (Lop) cylindricus X X X L/T - 6v3w incandescent light trap or co baited trap 2 M/B - Man biting collection R - Resting collection L - Larval collection . A~ r """ c.\ • ,._. rv- . . - .. - ---.. . --.. ·------MONTHLY MAXIMUM NUMBERS OF ADULT FEMALE MOSQUITOES PER CO2 TRAP NIGHT AT SITE •A•, IL PARPA SWAMP, ALICE SPRINGS. 1989. Anopheles Culex Culex Culex annulipes annulirostris australicus quinquefasciatus I I q ' ' J I f I ~~\S~l VZZ72l 900 T I : 800-~ I I . a.. ::JCJ ~no·-~ ... . U1 0 ~ IL 400 ' 7"" n I • i ~ 300 .._ I ~ l ~ I ;::. 200+ ~ I ~ ... ' I ··, 100~ " ' DW -~J ~ - O-t~ _kL _f~ . .:::. ' ~dflj ~~ wr JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV \ MONTH v I i L ____ . ·-