Vector mosquito survey, Nguiu Community, October 1981

Department of Health Library Services ePublications - Historical Collection

Please Note: Aboriginal and Torres Strait Islander people should be aware that this publication may contain images, voices or names of deceased persons in photographs, film, audio recordings or printed material.

Purpose

To apply preservation treatments, including digitisation, to a high value and vulnerable Historical collection of items held in the Darwin and Alice Springs libraries so that the items may be accessed without causing further damage to the original items and provide accessibility for stakeholders.

Reference and Research Disclaimer

Please note: this document is part of the Historical Collection and the information contained within may be out of date.

This copy is a reproduction of an original record. Please note that the quality of the original record may be poor and cannot be enhanced with the scanning process.

Northern Territory Department of Health Library Services Historical Collection

INTRODUCTION

VECTOR MOSQUITO SURVEY NGUIU COMMUNITY OCTOBER 1981

MEDICAL ENTOMOLOGY SECTION

NORTHERN TERRITORY DEPARTMENT OF HEALTH

Bathurst Island and the larger neighbouring Melville Island lie approximately 60 km north of Darwin.

The main population centre on Bathurst Island is the predomin- antly Aboriginal community at Nguiu, situated at the S.E. end.

At the time of the survey Nguiu community had a population of approximately 1300.

An officer from the NT Department of Heal th, Medical Entomology Section and the Regional Health Surveyor, Mr Richard Chippindall, visited the community from 26-29/10/81 to conduct an Aedes aegypti survey and to assess the likelihood of exposure of community members to vector mosquitoes.

Possible measures whereby this man/vector contact may be reduced are discussed.

METHOD

1.0 Aedes aegypti Surveys

The presence of Ae.aegypti was assessed by a comprehensive search within the community of containers likely to hold water. Containers with mosquito breeding were sampled for mature specimens of each of the different looking mosquito

larvae present.

DL HIST alcohol solution 595.772

DAV identification.

1981

These and

specimens returned

were preserved in to the laboratory

70%

for

.

^{' 2}

A man-biting catch and carbon dioxide (CO_{2 )} baited traps were used in the community to supplement this container breeding survey.

2.0 Vector Mosquito Surveys

Possible significant mosquito breeding sites near the community were determined by studying aerial photographs of the community environs. These sites were then investigated by CO₂ baited traps to determine mosquito species present and relative numbers. These CO₂ sites are marked on Figure 1. Larval surveys at these potential breeding sites were conducted to determine actual breeding sites of vector mosquitoes of concern. Knowledge of breeding sites utilised by these species, allowed potential breeding sites to be identified.

CO₂ baited traps were used within the community to assess the numbers of potential vector and nuisance mosquitoes present.

RESULTS

1.0 Ae.aegypti Survey

Results of the container breeding survey are displayed in Table 1. The ninety-four (94) premises searched produced a total of fifteen ( 15) containers holding water, of which eight (8) held mosquito breeding.

No larvae of Ae.aegypti were collected.

The single man-biting catch, conducted in the community area during the morning of 28 October, did not detect any mosquitoes (see bottom of Table 2.)

The CO₂ baited mosquito traps utilised in the vicinity of the community detected the presence of the important vector species Culex annulirostris t.the common banded mosquito' , Anopheles farauti 'the Australian malaria mosquito' and Aedes vigilax 'the saltmarsh mosquito'.

Ae. vigilax was the most commonly collected mosquito within the community.

Results of the CO₂ trap catches are presented in Table 2.

The larval survey at potential mosquito breeding sites near the community revealed breeding of ex. si tiens, ex. annuli- rostris, Ae.vigilax and An.hilli (see Table 3.)

Both known and potential mosquito breeding areas detected near the community are displayed in Figure 1.

DISCUSSION

1.0 Ae.aegypti Survey

Ideally, surveys for mosquitoes which typically breed in containers should be conducted late in the wet season when the incidence of such breeding sites would be expected to be highest. As

water located the average

expected the incidence of containers holding during the survey was substantially lower than for similar surveys conducted in 'top end' communities during the wet season.

Nevertheless the most commonly, collected container breeding mosquito was Ae. notoscriptus c3.nd as this mosquito utilises similar breeding sites as Ae.aegypti this is an indication that had Ae. aegypti been present in the community i t is likely i t would have been detected.

4

Ae.notoscriptus adults were also taken in two CO₂ traps . A follow-up survey conducted during the wet season is recommended to confirm this indicated Ae.aegypti free status.

2.0 Vector Mosquito Survey

2.1 Anopheles farauti 'The Australian Malaria Mosquito' Low numbers of An. farauti were collected in the CO₂ traps placed at four (4) sites near the margin of the mangrove area to the north of the cornrnrnuni ty. No specimens were taken in the CO₂ trap sited in the community. To the south of the community the coast adjacent to the old airstrip is free-draining mangroves at the base of low cliffs. Further south-west of the community, past the end of the old airstrip, the land slopes more gently to the mangroves and there is a thin margin of relatively flat land between. This area was traversed during the larval survey to a distance of apJ;)roxirnately two ( 2) kilometres from the community.

No significant potential breeding sites for An.farauti were detected along this margin al though some small potential breeding sites where freshwater run-off enters the mangroves were detected. These were dry at the time of the survey.

The mangrove margin to the north of the community between the darn and the sewerage ponds was free draining with the exception of one creek line which was dry at the time. Small areas of brackish water may occur at this site during the wet season, providing a suitable breeding site for this species. Adjacent to the cornrnuni ty between the coconut plantation and the dam, the mangrove margin receives run off from drains which would produce areas of brackish water at the mangrove margin during the wet season. At the time of the visit the drains were dry apart from the creek line

water (specific conductivity 47.0 mS/cm) breeding Cx.sitiens.

2.2 Culex annulirostris 'The·Common Banded Mosquito'

This species is the known vector of a number of arbo- viruses including those causing epidemic polyarthritis and Australian encephalitis. Sui table breeding sites for Cx.annulirostris include freshwater swamps and lagoons and areas of less permanent water such as those forming in low-lying grassy depressions following rain.

It also commonly breeds in sewerage ponds where grass growth at the margins prevents wave action.

At the time of the visit moderate numbers of Cx.annuli- rostris were collected in the CO₂ traps sited along the mangrove margin north of the community. No specimens were collected in the community or at the site adjacent to the mangroves near the new airstrip.

Highest numbers of Cx.annulirostris were taken from the site adjacent to the sewerage ponds. A larval survey detected low levels of breeding in the ponds amongst scum and a small amount of vegetative debris at the margins . If the scum was removed or broken up then wave action would be promoted thus preventing mosquito breeding. Continued maintenance of the margins in a weed free condition will also help promote wave action.

Excess final effluents are directed into a substantial salt-water creek adjacent to the ponds and so will not be a source of mosquitoes.

Significant numbers of Cx.,annulirostris were also taken in the CO₂ trap at the coconut plantation. A larval survey of the nearby area detected breeding of this species in a pool of polluted water adjacent to the low level sewerage pump station. Maintenance of the pump had required the emptying of the pipes into this area

6

producing a pool about 2 metres in diameter.

Cx.sitiens, Ae.vigilax and An.hilli were also detected breeding in this pond (see Table 3).

The aerial photographs af the communty did not reveal any significant fresh-water swamps in the environs.

However likely Cx. annulirostris breeding sites in the community area were recognised.

1. Low lying area behind the council office.

A number of depressions in this area are likely to become breeding sites for this species when they become filled with rainwater run-off during the wet season. Filling of these depressions or contouring of the area would remove these potential breeding sites.

2. Ill defined drainage line and borrow pits/low lying areas near the barge landing.

The low lying areas need to be filled and the drain formalised with culverts for the road. The drainage line which runs north from this area needs to be formalised so that all run-off can flow into the daily flushed mangrove area.

2.3 Aedes vigilax

At the time of the survey CO₂ trap catches of Ae. vigil ax near the community were high. Within the community area the CO₂ trap collected significantly lower numbers but still indicated a pest problem for community members.

Highest numbers were taken in the CO₂ trap adjacent to the drainage line from the dam near the community. The larval survey located breeding of

ex.

si tiens in this site. This species typically breeds in saltwater to

- I

brackish pools, often 1n association with Ae. vigil ax and An.hilli. The specific conductivity reading of 47.0 mS/cm indicated that the source of the water would have been the high tides during the period 14-17 October (salt water has a·-conductivity of approximately 55 mS/cm) which are likely to have penetrated to these upper reaches. The other possible reason for large catches in this area would be that i t was the principal mosquito harbourage in the area. However there were other suitable mosquito harbourage areas near the community. Thus the CO₂ trap catches of Ae.vigilax at this site and the decreasing size of catches more distant from this site, suggest this area was the principal source of Ae.vigilax in the community area.

Next highest catches were taken at the site near the new airstrip. High numbers of ex. si tiens were also collected, indicating a suitable breeding site relatively close by because this species is not known as a long distance flier.

Within the community a number of possible Ae. vigilax breeding sites were located although no larvae of this species were taken from these areas at the time of the survey. Areas located and possible means of rectifi- cation are:

1. Ill defined drainage line near barge landing.

Inspection of this drainage line showed i t was tidally influenced and unlikely to be free draining. A subsequent inspection by the NT Health Surveyor, Mr R. Chippindall, located breeding of Ae. vigil ax in the middle and upper reaches on 16 November 1982 (high tides, with a maximum of 7.9m, had occurred during 12-15 November).

·,.

8

This drain needs to be formalised and road culverts provided so that i t can be made free draining.

2. Some small low lying- areas around the boundary of the coconut plantation need to be filled so that they drain following high tides.

3. Low lying area to the rear of the council office.

Vegetation in this area indicated an occasional salt water influence. Inspection by Mr Chippindall on 16/11/82 revealed breeding of Ae. vigil ax in a number of depressions with the heaviest breeding in the vicinity of the low level sewerage pump station. A combination of filling and contouring is necessary to ensure this area is free draining.

CONCLUSIONS AND RECOMMENDATIONS

1. Ae.aegypti appears to be absent from Nguiu.

2. An.farauti was collected in low numbers near the community.

3.

Potential breeding sites appear to be where small creek lines and drains enter the mangroves. Close to the community the most important potential breeding sites are likely to be associated with the drains at the rear of the council yard. The formalisation of these drains and their continuation to the daily flushed mangrove margin would remove these potential breeding sites.

Cx.annulirostris was collected,in moderate numbers near the

I

community. No significant fr~shwater swamps/lagoons, that would be source of this species for the community, were evident in the aerial photographs.

Highest numbers were collected near to proven man-made breeding sites. Excess sewerage effluents are not a source of mosquitoes. Potential breeding sites in the community area could be rectified by filling and/or draining.

4. Ae. vigil ax is likely to be a problem in the community at various times during the period from the end of the 'dry' to the start of the 'wet' . The principal breeding site for this species _appears to be the poorly draining creek line that runs from the dam to the mangrove margin. If this creek line was made free draining the mosquito breeding would be prevented. As a short term alternative, chemical control using Temephos ('ABATE') at the rate of 5.6 ^gm per 10 square metres could be conducted when breeding was detected. Monitoring of this site is recommended two to three days after high tides and/or heavy rainfall. Some minor breeding sites in the community area could be rectified relatively easily by filling and/or draining.

G. Davis

Medical Entomology Section

14.8 B

I - '/I'-

TABLE 1

Aedes aegypti SURVEY NGUIU - OCTOBER 1981

PREMISES EXAMINED

Hospital

Accommodation next to mechanics yard

Pre-School

'Tiwi Design' Convent Flats

Baby Clinic House No ⁴

(on town plan) Washing facility near barge landing House nearest to low level sewage pump

Barge Landing

Aboriginal Housing 9 4 premi&s"

TOTALS

CONTAINERS WITH WATER NC. TYPE

2 1

2

2

3

1 1

1

1

1

Unscreened rainwater tanks Screened rainwater tank

Truck Tyres

Screened rainwater tanks Glass jars with plant cuttings

Plastic Bowl Potted Plant

Wash Trough

Washing Machine

3m Wooden boat Nil

104 Premises Examined ,

SPECIES OF LARVAE

ex. quinquef ascia tus

(i)

ex. halifaxii

(0

Ae. notoscriptus

(2)

Ae. notoscriptus

ex. quinquefasciatus

Ae. notoscriptus

ex. quinquefasciatus

5 Premises with mosqµito breeding 15 Containers with water

8 Containers with mosquito breeding 3 Mosquito species represented

SPECIES COLLECTED

~ ~ ~ ~ ~ ~ ~ ~ ^{() () () C t-3}

(D (D (D (D (D (D :::s X X X ~ 0

. ~)CATION _DATE

. . .

^t-3

Ul ~

p., _I-ti :,<;" :::s rt <: I-ti ::,-" p.,

~ ^{I-'· p.,}

f-' ~ 0 0 ~ I-'· p., I-'· :::s rt ^{I-' (/)}

rt :::s 0 rt ^{(D LQ} ~ I-' :::s ^{I-'· I-'·} tr

(0 (D ::,-" 0 § ^{I-'· p., I-' ~ :::s (D (D}

r, _{~ I-'· Ul I-'} C ^{I-'· I-'} ~ :::s Ul

:::J (D 0 I-'

~ ^{rt I-'· C en 0}

PJ C ~ C I-'· _~ (D (D

:::J en I-'· en 0 I-ti :::s

(fj to en p., Ul

rt rt ^Ul

C ~ ()

Ul I-'· I-'·

Ul p.,

rt C Ul

At rear of Council yard 27/10/1981 2 3 270 9 44 1 32.lJ

Coconut Plantation 27/10/1981 2

i

^{193 2 50 2}

a.+'1

Adjacent to visitors accommodation 27/10/1981

I

^{I 1 72 8 3}

(in community area) ^I

i4-

I

I I

.. I

I

^{I I I I}

6'5:S

At rear of Council yard 28/10/1981 1 ^I 8 I 4 584 12 2 40 4

i i !

:

i

! ^I

I

Adjacent to sewage ponds on roa,d to 28/10/1981 3

!

I

540

I

10 84 8

(,4-S

outfall

i

I

I ^{I I}

On creek line from dam near community 28/10/l98l 1 _I 8 1 908 10 2 44 16

9'lO

at mangrove margin

I I

I I I

SW from community where creek line

I

^I I _I

8Gt;

enters mangrove margin, next to airstrip! 29./10/l981 ! ^I _I 1 ^I 750 1 114 I

I

I I

I I I I ^I

Adjacent to creek line from dam near I 6V/3W LIGHT-TRfiP I

14-2

I ^{I I I}

I

^!103

Community 2711011981 I ⁱ 2 . 2 3 28 3 1

I l I I

I ! ^I

MAN BITING CAT '.:H ^{I I}

I i

I

I

Front yard of house adjacent (SW) to 28/10/1981 ^I NII µ CAT< 'H ⁽

I

! (

hospital. Time - i ^: ..

0645-0715 hrr ^{I ~}

I

I

..._

I -

Table 3. VECTOR MOSQUITO SURVEY NGUIU ... OCTOBER l9.8J.

LARVAL COLLECTIONS

DATE BREEDING SITE

.27/10/1981 Large pool of polluted water, sunlit grassy margin. Produced by pipe clearing at nearby sewage pump, water sample

600/ls/cm

SPECIES COLLECTED

Culex sitiens

Culex annulirostris Aedes vigilax

Anopheles hilli

-- '""'" ..

-

/

27/10/l98l Polluted water held in blocked drain of ablution block.

Culex quinquefasciatus

28/10/1981 Drainage line from dam Cnear community;) Culex sitiens to mangrove margin. waTe'I" ^$an\~ 41·0 rn S/cm.

28/10/1981 Crab hole at mangrove margin near community

Water sample 50.SmS/cm

Aedes longirostris

\ _\.-

- - --- ----

- N .

i

⁰ _I

• ro::z..

-zg/,o

250m

I

SCAL~

500rf\

I

AREA

-- -

^--\

-- -

--- --- -- -

('f•C.X'(jfcNe,S

~~Boocl~

~\or\ol C\ I•

s-cJt u.,o.11,r "( 004'~

mvJ t\al:.

sc:Jt-w~

\1\ C>Jf' sim'\

c.reJ(₁

dr~

_...-l

~~\)(€-

I..

NSU\U COMMUN\Tf and e:.NVl'ZON'S

October \

9

^{<3 l}

MEDICAL ENTOMOLOGY.

N.T. HEALTH - Of"RWiN

.

^..

i"nos'Q.u\10 b~C-Q)1N~ S4RV1z_'('

P~eE

N ~Lu ^L{

1

t

ATH-e<. ~5T

r.s

^hJt-N})

DA-TE l

6

^{N.o v ~)c~~}

t q

^{& 1}

I

\\vY\~ I J.+. i>O - i (, C)O •

I •

CLv-- ~~

1

f ' ~ { . ~ ^{, R _ ~} olA-~/ ~'~ f-o t ~

~~~ ~ 0 - V - - - - ~ ~~ ~ ~ ~~.

• . J . f"\"\ J ol.d 1-L '-"-""'-<-~ '

t) bA-J2.JL ~ ^u.._r-o-o ~~ ^;__ <t-Wi.-;\

+~

^{~ ~ ~ ~ ~}

~ +1..-:L ~~ ~ o . . _ ~ ~ ^~Le... -h-~_k .0 ·~~ ;

2) ~ ~

~ - ~°'

^{cJ--? o-v--,Q- ~-e..ol} c.X-<.-~ ·h +t-_ ~ ^j

3) ~~ o - c _ _ ~ , J . . ~ ~ ^{~ 0 - -}

41'-~

~

-'~ /.

'+) ~4~ ~ c , . . _,lr---LL . , t ~ ~ ~ ~ t - . , _0 ~ ~ o - ~ <Y"'--

-+~ ~

^{~ ~ ~}

cc)

^,Z v ~ ~ ,

-:).k_ ~ J - _ ~~) L-e-~,-~_) ~ ~ c.,J

01p:.

^{C'.L ) L ~ - ~}

~~ ^{0 - ~} ~~~ o-S ~ , ~ - - - ~ ~

~ : ·_s~

~~ ~

'-'-'~- ,,,r ~ *

^{---Z~ ~~ ~ er'-- ~ ,,,,~}

·~. . ) _ , ~

~----

^~

.

l{\,'-1..,~ ~ ~ - ~ ~ ___,_:__c,L._ ~ f ~

0 - - - f~~

/ ~\.__

^~

v-~

^{~ ~ ·i-~ .}

- - -- . . z ~

^{~ ~ ~ ~ V0L-~ ~} ·-t--\-:L.

_,,,_,,, _,,,,.- - ^. ~

(~ ~ ~

¹

~~ ~ ~

~ c A _ . ~ ~ L ~ ; t ~

~ c J ~ ~ J - - ~ ~ . ~ - ~ --- --t-~.

~~ ~ -~ ~ ~~ + ~ ~ J ; +~

/p

^~

(

^{~ ~ ~~~l}

O-<:_c_o.-,~4 { ~

^i-l-.c_

~ ~ ) ~ ~o\. ~~\.----

~>-*-~~

~~ -\-L-z_ ' - " - ' ~ .

(L-v-_ \ . ~ e-e-v-c_:~ .. , v ,. / ~ ~ ~

--p

~'--',_/~J '-"-~'-₁ ~ ~

~ ~ ^{. A _ ~} ~ ~ ^{~ C7\.,_} ~ JL.,~ ~ ~ -

-~ C ~ ~ ~ ^•

~ ~ ^c--- I

t

l \ ~ ~ ' - - -

1 \ C\.

t \

~~o-lJ...cA ~L-..~

~ - ~~ k,-c>-. ~ o--J

a-.-A

,t-4 ~~ ~ ~~ .:-~ ~

·V\'v\-LA ~ ~ . , , t ~ ~c:;Lu...c..s....o' ~ ~ G L -t,-LL,J ,