Vector mosquito survey, Maningrida, April 1984

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Northern Territory Department of Health Library Services Historical Collection

DL HIST 595.772 DAV 1984

VECTOR MOSQUITO SURVEY MANIN GRID A

APRIL 1984

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HISTORICAL COLLECTION

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VECTOR MOSQUITO SURVEY - MANINGRIDA - APRIL 1984 N.T. DEPARTMENT OF HEALTH

MEDICAL ENTOMOLOGY BRANCH

INTRODUCTION

CENTRAL LIBRARY

- 6 MAR 1998

TERRITORY HEAL TH SERVICES

The Aboriginal Community of Maningrida is situated within the Arnhem Land reserve on the north coast of the Northern Territory approximately 370 kilometres east of Darwin.

The community is sited at the mouth of the Liverpool River and is bounded by medium density forest (see location map, Figure 1).

At the time of the survey the population of the community, including those people at the 25 outstations, was about 1000.

The town clerk was Peter Clark and the council president was Charlie Yirrawalla. Two off ice rs from the Medical Entomology Branch, Mr Geoff Davis, Medical Entomologist and Ms Wendy Kelton, Technical Officer visited the community during the period 3 - 6 April 1984 to conduct a vector mosquito survey.

Although it is usual for surveys to include a container-breeding mosquito survey to check for the presence of Aedes aegypti, the recognised vector of dengue fever virus in Australia, no survey was conducted because it was expected this community would be surveyed for this species as part of the Commonwealth Department of Health funded Mosquito Eradication Campaign.

This community was last surveyed for disease vector mosquitoes in March 1981, however, heavy rainfall during the survey period hampered the field activities. This follow-up survey was considered necessary to more accurately define the presence and location of the important vector mosquito sources in the community environs.

2. 0 METHOD

Vector mosquito activity in the community and environs was surveyed by the use of carbon dioxide (CO) baited light traps.

Thirteen traps were operated at various sftes within and on the margins of the residential area to assess mosquito breeding and activity in the community. Nine traps were operated in the community environs to examine either mosquito movement toward the community or mosquito activity at mosquito breeding sites likely to be of significance to the community.

These co

2 traps were operated from before sundown to approximately one or two hours after sunrise. The catches were killed with chloroform and stored in crush proof containers with dry packing. All identifications were conducted at the Medical Entomology Laboratory in Darwin.

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Larval surveys were also conducted in those 1 ikely important mosquito breeding areas in the community environs. Larvae collected were preserved in 70~ alcohol and returned to the Medical Entomology Laboratory for identification.

3.0 RESULTS

A total of 12,941 mosquitoes of 31 different species were collected in the 20 co

2 baited light traps (CO₂ traps) operated in and around the Maningrida community. The CO

2 trap locations used are marked on figures 1 and 2. The co

2 Erap results are presented in table 1.

The 9 most commonly collected species accounted for 96.8% of the total catch, with Culex annulirostris being by far the most commonly caught species (68.1% of the total catch).

Anopheles farauti was collected in significant numbers in the co₂ baited traps at many sites around the community. Aedes vigilax was collected in generally relatively minor numbers.

No Aedes aegypti were collected in the co

2 traps around the community.

The findings of the larval survey are represented in Table 3.

4.0 DISCUSSION

4.1 CULEX SPECIES

4.1.1 Culex annulirostris - the common banded mosquito.

As already .mentioned, Culex annulirostris accounted for 68% of the total mosquito catch taken in the CO traps around the Maningrida community. This result is 2t_ypical for coastal communities, in the vicinity of freshwater swamps, at this time of year and indicates a high level of nuisance in the c"ommunity and a potential for the transmission of the arboviruses this species is known to vector.

In general the freshwater swamps around the community were shown to be prolific sources of Cul ex annulirostris and the numbers of this species in the community were moderate. Breeding of this species was detected in many areas in and around the community (see Table 3).

High numbers of Cul ex annuli rostris were present in the community in the vicinity of the small drainage line (Site 14), 'Leper's Hole' (Site 17), near 'Top Camp' (Site 18) and the s awm i 11 ( S i t e 1 9 ) • Low 1 eve 1 s of Cu 1 ex annulirostris activity were indicated in the vicinity of the N.T. Health accommodation (see table 1).

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The

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₂ trap survey indicated 'Leper's Hole' was the most important source of Culex annulirostris for the community.

The 1981 survey found this area to be of minor importance as a source of ex. annulirostris. Breeding of this species was detected at this site (see Table 3). If possible, this swamp should be removed or at least greatly reduced in size by the use of a short drain to the sea or perhaps some filling. 'Leper's Hole' has the potential to become an even more prolific source of Culex annulirostris if this area were to become polluted with community rubbish or perhaps the outflows from urban drains.

The small drainage line which enters the Liverpool River near the barge landing is mostly ill-defined in its upper reaches and breeding of Culex annulirostris was detected in this area (table 3). Formalisation of this creek into a single shallow drain from the vicinity of the saw mill to the culvert on the community road (see Figure 2) would allow waters in this area to be drained relatively quickly to the sea. The side entry drains from the community would also need to be joined formally into this drain.

With ongoing maintenance this drain system would remove an important source of Culex annulirostris close to the community.

The relatively low numbers of Culex annulirostris taken in the CO? traps at the Northern Territory Health Department accommcrdation (Site 9, Table 1) and on the western side of the airstrip (Site 15) are evidence of the value of an open area (Buffer Zone) in interrupting mosquito dispersal. The large rectangular area of open ground on the eastern margin of the community associated with the airstrip is likely to discourage mosquito movement into the community from the swamp areas to the east. This is particularly important in the light of the high levels of Culex annulirostris activity indicated in the forest area to the east of the community - the CO? trap at sites 1 and 13 collected the highest numbers- of this species relatively close to the community.

South and West of the community no such buffer exists and dispersal of Cx. annulirostris from breeding sites in these directions would probably result in high numbers of this species being present at these borders of the community. This expectation is confirmed by the high numbers of Cx. annulirostris taken in the

co

₂ traps at the sawmill and 'Top Camp' (see table 1).

The sewerage ponds were found to be fairly weed free and no breeding of Cx. annulirostris was found in them. Excess effluent is piped out into the Liverpool River.

4.1.2. Culex sitiens

Culex sitiens was collected in significant numbers in the

co

₂ traps sited at 'Leper's Hole'. This species breeds in brackish to salt-water areas. Collection of this species

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and another brackish water/salt-water breeder (Anopheles hilli) indicates there is probably a salt-water influenced breeding site in the vicinity of 'Leper's Hole'. Such a breeding site has the possibility of being a source of the important potential disease vectors Anopheles farauti s.l.

and Aedes vigilax, at certain times of the year. The larval survey of 'Leper's Hole' did not detect breeding of Cx. sitiens or An. hilli. A more thorough examination of this area shoulcr-be conducted to locate the breeding site so that a control measure such as draining or filling (if the site is relatively small) could be undertaken to remove this breeding site.

Culex pullus

Culex pullus accounted for a significant proportion of the total mosquito catch ( 3. 35%) with by far the greatest number being taken in the

co

2 traps sited at the Leper's Ho 1 e swamp ( S i t e 1 7 , F i g u re 1 ) • Th is spec i es is not a man-biting mosquito and therefore is of little health

importance.

4.2 ANOPHELES SPECIES

4.2.1 Anopheles farauti s.l. - the Australian malaria mosquito Few Anopheles farauti s.l. were collected during the 1981 survey and comparisons with this later survey are limited because of the few CO? traps operated in the vicinity of potential An. farauti s.l. breeding sites.

In 1984 Anopheles farauti s.l. was by far the most commonly collected anopheline in the community environs.

In general no specimens or only low numbers of An. farauti s . l . , were collected in the

co

₂ traps sited in the community. The exceptions were those

co

₂ trap catches at Sites 14 and 18. The collection of 35 An. farauti s.l. at Site 14, in the community area, indicates that suitable breeding sites may be present in the vicinity. If these breeding sites are freshwater (suitable for An. farauti No. 3) then a likely source of this species close to the community would be removed by the formalisation of the upper reaches of this drainage system ( see 4 .1.1). Such numbers of An. farauti s.l. indicate a receptivity to malaria transmission in those areas of the community adjacent to the lower reaches of this creek. Similar numbers at Site 18 are most likely due to dispersal from the swamp 2 kilometres Southwest of the community which was shown to be a prolific source of An. farauti s. l. (CO trap Site 10). 2

These two trap results indicate that Maningrida community is receptive to malaria transmission with the risk being greatest along the Western margin of the community. The high numbers of An. farauti s.l. collected at Sites 1 and

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12 indicate that there are significant breeding sites to the East of the community. A number of swamp areas in this direction were sampled during the larval survey but no specimens of An. farauti s.l. were collected.

A comparison of An. farauti s.l. catches from traps 15 and 16 highlights the effect of the open area in reducing dispersal of this species from breeding sites to the East,

into the community.

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4.2.2 Anopheles meraukensis and Anopheles novaguinensis

4.3 4. 3 .1

Anopheles meraukensis and Anopheles novaguinensis were the next most commonly collected anophelines in the CO

2 traps, accounting for 3.04% and 2.51% of the totaI catch . respectively. In 1981 very few An. meraukensis and no An.

novaguinensis were collected in the CO trap program. An.

novaguinensis is not a proven vector of malaria in Australia and An. meraukensis is considered to be a suspected but unproven malaria vector. The low numbers of these two species are unlikely to contribute significantly to the malaria receptivity of the community, however they could be a nuisance in some areas of the community at times generally during the middle to late Wet season and early Dry season.

AEDES SPECIES Aedes reesi

High numbers of Aedes reesi were collected in the co

2 trap at the crossing on Gudjerama creek (Site 12). This species is currently thought to breed in periodically flooded ground pools and is a keen man-biter, during the day, in the shaded harbouring areas near its breeding sites. As Ae. reesi does not usually travel far from its breeding sites in appreciable numbers, it is unlikely to be a problem in the community. This species is not recognised as an important vector of human disease.

4.3.2 Aedes vigilax - the saltmarsh mosquito

Small to moderate numbers of Aedes vigilax were collected in the co

2 traps in and around the community. Very few Ae. vigilax were taken in the 1981 survey. The larval survey of brackish water areas in the community environs did not detect any breeding of this species, however a number of potential significant breeding sites were identified (see Figure 1). The most important likely breeding site located lies approximately 5 kilometres E of the community and is so extensive in area that breeding of Ae. vigilax throughout this site could probably result in plague numbers of this species in the community at times -

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Ae. vigilax being well known to disperse long distances from its breeding sites. Smaller size potential breeding sites were also located about 1 3/4 kilometre ENE of the community (see Figure 1) and in the brackish water swamp area approximately 2 kilometres SW of the community

(vicinity of

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₂ trap site 10, Figure 1).

All three Ae. vigilax breeding sites mentioned above are probably the principal sources of the plagues of this species which ·are known to occur in the Maningrida community later in the year - following flooding of their breeding sites by the particularly high tides which are most common at this time or by early wet season rains.

These plagues present not only a great nuisance but a potential risk for the transmission of the arbovirus which causes epidemic polyarthritis.

To confirm these breeding sites, larval surveys should be conducted in these areas late in the Dry season, a few days after the particularly high tides which occur at this time of year. Once these three areas are known to be important breeding sites and have been delineated then consideration could be given to control methods. The most practical chemical control method would be larviciding using a back-pack motorised machine applying the larvicide based on Bacillus thurinqiensis var.

israelensis

(B.t.i.).

Physical control methods such as draining may also be consider:-ed.

Coguillettidia xanthogaster

Coquillettidia xanthogaster was the next most · commonly collected mosquito ·Species after Culex annulirostris,with 8.15% of the total catch. The majority of the

co

2 traps operated within the community indicated little activity of this species, however the two traps at Sites 18 and 19 demonstrated that dispersal from freshwater breeding sites, in these directions, can probably result in nuisance numbers of this species in the community at times.

~ . x ant hog aster breeds in sun 1 i t we 11 vegetated swampy areas where its larvae attach themselves to the roots and stems of certain aquatic plants to gain air. The larval survey in the community environs revealed a number of likely breeding sites for this species. The most important likely sources of this species being the drainage line S of the community (CO

2 traps 5, 6; Figure 1), the lower reaches of Gudjerama creek and the reed swamp 1 3/4km ENE of the comrnuni ty. As ~ - xanthogaster ig recognised as having a long flight range (in the order of a few kilometres) then even those sites a few kilometres distant could be a significant source of this nuisance. The most practical method for reducing the nuisance due to

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xanthogaster would be self-protection measures using repellants, protective clothing and screening of premises. ~ . xanthogaster is not known as a vector of human disease in Australia.

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4.5 RISK OF MOSQUITO EXPOSURE

As with the majority of aboriginal communities surveyed, a lack of effective insect screening on houses and a preference to relax and sleep in the open predispose the majority of the residents of Maningrida to mosquito attack.

Many older premises and particularly those at 'top camp' had neither insect screening nor doors and thus provided virtually no protection from mosquitoes. This situation, in combination with the relatively high level of mosquito activity at this margin of the community means that the residents of 'top camp' probably suffer the highest levels of mosquito attack in the community.

In recognition of the problems presented by mosquitoes in the Maningrida community (risk of disease transmission, nuisance) a public education program should be used. As an annual activity i t could inform people about the disease risks and publicise the appropriate self- protection and avoidance measures. An awareness of container breeding mosquitoes would be usefull in reducing the problems due to peri-domestic mosquito breeding and would result in the community being less receptive to the introduction of Ae. aegypti.

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Certain mosquito species, including Cx. annulirostris, Ae.

vigilax, An. farauti, An. meraukensis and

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xanthogaster, are likely to be a problem in some parts of the Maningrida community at times, not only as nuisances but often as a potential risk for the transmission of some human diseases.

5.2

5.3

Some rectification measures such as drainage and filling, are recommended in and around the community to reduce the mosquito problem.

The maintenance and, if possible, extension of a buffer zone around the community will be of value in discouraging mosquito dispersal into the community from distant breeding sites. This extension should include the whole southern margin of the community, from the sawmill to 'top camp' and should be at least as wide as the airstrip corridoor.

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5.4 Aedes vigilax potential breeding sites located around the community should be confirmed as the source/s of the plagues occurring in the community at times. Once these sites are confirmed control options should be considered.

5.5 It is recommended that the forestry access tracks on the southern margin of the community be maintained so that they can be used as vector control access tracks following an outbreak of mosquito-born disease.

5.6 A Health Education program should be run annually to inform the residents of Maningrida about the health risks of mosquitoes and the best methods of protection.

This survey has been assisted by Commonwealth Funding under the National Disease Control program.

G. Davis

Medical Entomologist

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^Kelton

Technical Officer

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TABLE 2 VECTOR MOSQUITO SURVEY MANINGRIDA

DATE LOCATION

4. 4. 84 Coastline 1. 25km NE of community.

4. 4. 84 Coastline 1. 75km

NE of community.

4. 4. 84 Coastline 1. 75km

NE of community.

5. 4. 8 4 Brackish sKamp, 5km E of community.

5. 4. 84 Drainage line, 3km E of community.

5. 4. 84 Coastline 2km SK of community.

5. 4. 84 Coastline 2km SH of community.

6. 4. 86 Seepage pool on coast in community ' Lepers Hole'

LARVAL COLLECTIONS

BREEDING SITE

Shallow, shaded, fresh- Rater pool (1m diameter) beneath Helaleuca sp.

grassy margin, leaf matter and algae, nil fish but other predators present.

Shallow, partly shaded pools betKeen mangroves and grass/Helaleucas.

Leaf matter, bro Rn a 1 gae, ni 1 predators.

Amongst organic matter, margin of extensive reed area, predators,

partial shade.

In organic matter, margin of reed area, part shade, predators.

ShalloR, grassy sKamp at edge of reed area, part shade, predators. ShalloK pool between old dunes, part shaded, grassy at margin and leaf matter.

Shallow, grassy swamp beloR Helaleucas and brackish water fern, at margin of reed area.

Organic debris and preda tot's.

Shallow, part shade, little grass and broKn algae.

margin.

Ferns at

6. 4. 84 Creekline adjacent ShalloK, part shaded pool to community. Ki th little grass, algae,

fish and other predators.

APRIL 1984

SPECIES COLLECTED Cx. annulirostris Ur. lateralis

Cx. species 167

Cx. annulirostris Cx. species 167 Ur. al bescens

Cx. Ur.

Cx.

Ur.

Cx.

annulirostris lateralis

species 167 tibialis

species 167

ex. annulirostris Cx. species 32 Cx. species 167 ex. squamosus An. bancroftii

Cx. species 167 Cx. annuli rostri s

Cx. annulirostris An. annuli pes

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