Mosquito investigations Adelaide River

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Northern Territory Department of Health Library Services Historical Collection

DL HIST

614.4323

HAY

1993

MOSQUITO INVESTIGATION ADELAIDE RIVE~

1. BACKGROUND

On February 12 1993 the Medical Entomology Branch received a request from Mr Roger Teague of the Coomalie Council to investigate the mosquito problem in Adelaide River. This request was a result of numerous mosquito complaints from Adelaide River residents. In response, two officers from the Medical Entomology Branch went to Adelaide river on February 1 7 to investigate the problem.

METHOD

Adult mosquito numbers were determined at various locations (see fig. 1) by the use of CO2 baited EVS traps. These traps were set on February 17 before sundown and collected after sunrise on February 18. Identifications of mosquito species and estimates of numbers were then made. Accurate counts were made later in Darwin.

Larval surveys were conducted at potential breeding sites (see fig 1), on February 18. The sites were chosen using the information gained from the adult trap catches, past surveys and maps~

2. RESULTS

2.1 ADULT TRAP RESULTS

Results from

co

2 baited adult mosquito traps set on February 17 are shown in table 1. Locations of adult trap positions are shown in Figure 1.

A total of 7246 mosquitoes were trapped from 9 trap sites, representing 19 species. The majority of these (87%) were Cx annulirostris, followed by Cx pullus (7.6%), Ae notoscriptus (1.35%), Ae reesi (1.17%), An meraukensis (0.65%), An bancroftii (0.32%), Ae lineatopennis (0.37%), Ae normanensis (0.36%), Ae vigila.x (0.12%) and other minor species recorded in table 1.

The majority 1804 (25%) of total mosquitoes were recorded from the trap adjacent to the Adelaide River Sewage Ponds. Of those 1670 (93 %) were ex annulirostris. Trap site 1 at the end of Strickland Rd, approximately 5 km from the town recorded the next highest with 1151 mosquitoes, (16% of the total). Of these, 1030 (89%) were ex annulirostris. Trap results up to 2km either site of the town ranged from 572 to 932 mosquitoes. Trap results along the river bank on the town side ranged from 704 to 741 and in the town centre 297 to 388.

2.2 LARVAL SURVEY RESULTS

Larval survey results conducted on February 18 1993 are summarised in table 2 and figure 2. The evaporation ponds (photos 3-5) had abundant weed growth around the perimeter. The water level was below the sloping concrete edges and was breeding high numbers of Cx annulirostris.

Low numbers of Cx annulirostris were found breeding in the storm water drain outlet behind Hatt St. This was also overgrown with grass (see photo

l)L 1- I .)T - ...i ,J ..::~~

Hf 1

Larval surveys were conducted at low lying areas around the town, (see table 2 and figure 1) but no breeding was found.

2.3 RAINFALL

No official rainfall records from the Adelaide River township were available.

Rainfall data from the official gauge at Batchelor is shown in figure 4. This shows that rainfall in the general area was relatively high from February 1- 12, 2 weeks prior to the investigation.

3 DISCUSSION

The two most abundant mosquitoes were ex annulirostris (87%) and ex pullus (7 .6%). Birds are the preferred host of ex pull us, it does not readily bite humans and is therefore of minor importance.

ex annulirostris "the common banded mosquito" is the confirmed vector of Murray Valley Encephalitis virus in Australia and is capable of carrying Ross River Virus, Barmah forest and Kunjin virus. It breeds in freshwater swamps, pools, streams, storm water drains and rainfilled depressions usually associated with vegetation. The most prolific breeding places are in sites with high organic levels such as secondary sewage treatment and evaporation ponds. The larvae are most frequently found in still, sheltered areas at the margins were vegetation offers protection from disruptive wave action and aquatic predators. (Whelan 1988)

ex annulirostris can fly 4-10km from its breeding site. It generally bites only after sundown and is less persistent in the presence of lights, repellents and protective clothing. The pest threshold for ex annulirostris in the Darwin area is 600 per

co

2 trap per night, in traps bordering the suburbs.

Trap catches at Adelaide river therefore indicate pest levels.

The Adelaide river sewage ponds are located approximately 500 m from the residential area and will be even closer if the proposed future subdivision shown in figure 3 is to go ahead. Adult trap results and larval surveys indicated that the sewage ponds were a major contributing source of Cx annulirostris near the town. High numbers around the river bank were expected as mosquitoes generally disperse and harbour in cool, damp dark areas such as river banks. Numbers in the town centre are reduced mainly due to competing light sources and animals.

The high numbers of mosquitoes caught in traps 2km south of the town indicated that there is a reasonably high background level of ex annulirostris in the Adelaide river area due to low lying rainfilled areas around the town.

ex annulirostris numbers would increase in the early wet season with the initial filling of swamps and lagoons and before biological control by aquatic bugs, beetles and fish is established.

Discussions with Don Roebuck and Roger Teague of the Coomalie council indicated that the mosquito numbers had decreased at the time of the survey.

People reported being viciously bitten at all times of the day. This biting habit is very uncharacteristic of Cx annulirostris and more typical of certain Aedes species such as; Aedes vigilax, Aedes normanensis and Ae lineatopennis, whose pest thresholds by comparison are 50 per

co

2 trap per night. Very low numbers of these species were recorded in the traps at the

2

· ..

time· of the survey. It is however possible that there may have been high numbers in the previous week.

These Aedes species may have come from rain filled depressions or coastal areas. " Evaporation ponds that dry up and are then seasonally inundated during rainy periods can become breeding grounds for floodwater mosquitoes such as Aedes normanensis." (Whelan 1988)

Another mosquito caught in significant numbers was Ae notoscriptus with 64 at site 7 and 28 at site 8. The natural breeding places are tree holes, rockpools and fallen palm fronds. This mosquito is domestic in settled areas and breeds in all types of artificial containers such as tyres, tins, drums or domestic water tanks.

4. CONCLUSIONS

The majority of mosquitoes at pest levels in Adelaide River at the time of the survey were ex annulirostris. The mosquito breeding in the Adelaide River sewage ponds was the most significant source. This was contributing to an existing level of ex annulirostris which is probably normally tolerated by Adelaide river residents. These two-sources along with the possibility of a hatch of Aedes species would have increased mosquito numbers to pest levels and would have led to the numerous mosquito complaints.

5. RECOMMENDATIONS

The first priority is reduction of the prolific source closest to the people.

Larval control should be conducted at the sewage ponds using Bacillus thuringiensis var. isralensis which will have minimal effect on biological control agents. This should be immediately followed by the application of weedicide. Follow up larviciding should be conducted weekly until vegetation has been killed and removed to allow aquatic predators access to mosquito larvae. Regular maintenance programs should be carried out, particularly in the wet season.

For evaporation ponds a depth of two metres or more is recommended to prevent the continuous growth of semi aquatic weeds unless regular edge maintenance is conducted (Whelan 1988). Other aspects to reduce mosquito breeding include; levelling of the floor of the evaporation pond, division of the area into smaller areas, construction of a sloping floor to concentrate the water in a sink area and concrete lining of the margins where the normal water level fluctuations occur.

Recommendations regarding design of sewage ponds breeding are outlined in Appendix 1 "Mosquito treatment in the NT" (Whelan 1988).

to prevent mosquito Breeding and Sewage

The open unlined drain behind Hatt St should be treated with Bti (Skeetal) and cleared of vegetation to assist run off.

Due to the vector potential of ex annulirostris, it is recommended that a public education program with regard to personal protection be implemented.

3

FOLLOW UP

Pamphlets were given to Coomalie council for distribution. Discussions with Roger Teague indicated that the Hatt St. drain would be weedicided and cleaned out.

Discussions with Geoff Butler from the Power and Water authority led to treatment of the Adelaide River Sewage ponds on the February 20 1993 with follow up maintenance programs anticipated.

REFERENCES

Whelan P I ( 1988) "Mosquito Breeding and sewage treatment in the Northern Territory"

Whelan PI & Hayes G A ( 1993) " Biting insect investigations Darwin South"

Marks E (1982), "An atlas of common Queensland mosquitoes" Q I M R Revised Edition with a "Guide to common Queensland biting midges" by Reye E.J.

4

ao~

₈

s

PHOTO 1: ADELAIDE RIVER SEWAGE PONDS. PRIMARY POND, STRAIGHT CONCRETE SIDES, FREE OF VEGETATION AND NO MOSQUITO BREEDING

PHOTO 2: SECONDARY PONDS. SLOPING CONCRETE SIDES. WATER LEVEL MAINTAINED. SOME VEGETATION STARTING TO GROW AROUND EDGES. NO MOSQUITO BREEDING.

PHOTOS 3 & 4: EVAPORATION POND. WATER LEVEL BELOW CONCRETE EDGE.

ABUNDANT VEGETATION GROWTH AND HIGH NUMBERS OF MOSQUITO LARVAE.

6

PHOTO 5: CONCRETE DRAIN BEHIND OUTLET OF EVAPORATION POND.

ORGANIC LEVELS. MOSQUITO LARVAE 200-300/DlP

PHOTO 6: OUTLET ORGANIC LEVELS.

DRAIN TO SNAKE CREEK MOSQUITO LARVAE 100/DIP.

HEAVILY VEGETATED,

HIGH

HIGH

PHOTO 7: DRAIN BEHIND HATT ST. OVERGROWN WITH GRASS. LOW NUMBERS OF MOSQUITO BREEDING.

8

.. .

TABl.E 1 AllJLT ~ CAOOHI' AT VARIOOS S ~ USOO rARllW DIOXIDE ^BAiffl) 1'DQJTIO 'TRAPS ADElAIDE llIVm FmRUARY 18 1993

STI'E lOCATim K~II10 SPEO~

rorm;

'Is CF

K).

An JruiJ IAn ~la~is

^Ae

kochi I I Ae notoocnpt.us I . I I A.e stoneorun I I

ex

b1taemorhynclrus rur . I . I

albescens ^'llJl'AlS

An bancroft.ii ~e allmcutellatus Ae lineatopennis Ae pecuniosus Ae viglax jCx

pullus

An

hilli Ae elchoensis Ae normanensis Ae reesi

Cx

ammlirostris

Cq

xant riogaster

1

^{EiMl of Stri l"lr 1 ~} 7 3 ^] 3 13

11

20 10.iU 13 ^{'/':, i]}

1151 15.8b

M.

m

Adelaide R.

bank.

12 ()} roadside where

1 11 14 b 4 6 ':,9'/

12

¹³⁴ 12 657

9.m

snake <le. crosses Stuart Hwy. 1. 5Jan

North of t<Ml.

13

MJarent to

17 114 14 llb'/0 14 1105 1804 24.90

Adelaide R.

Sewage

lulds.

14

Swarmel St.

11 11 11 12 12 13 '2b0 12·, 297 4.10

15 School y1• •n•~H 11 11 1 12 2 ¹²

J,n

152 ^]88 5.3~

6 Mmorial

Park

8 2 3 1~ 2 5 ~53 2 109 ~ 704 9.

1 : ·

7

Between nver

and 3 b b ^] 16 164 -g-- _{3 :6U}

741

10.2]

lbtel. Ol river bank.

8

Over bndge.

Sooth 1 1 1 4 28

12

422 ~b l 5"/2

7.8~

of town.

~

the oorner of the soowgromds road.

19 12km

Sooth of

11 !Y ^1f> 11 6 ^{'/,'/ '/} 11 IHW ^I]

,~

^{11 932}

12.86

Adelaide River

m

roadside.

TABLE 2 LARVAL SAMPLE SITES ADELAIDE RIVER FEBRUARY 18 1993

SITE NO LOCATION NO/DIP SPECIES

1 Adelaide River 20-30

ex

annulirostris

sewage ponds. 30-50

ex

annulirostris

50-100

ex

annulirostris 100-300

ex

annulirostris (See fig 2)

2 Storm water drain 5-10/dip

ex

ann ulirostris at the end of Hatt St.

3 Low lying area to nil

the east of the sewage ponds

4 Low lying area nil

beside Stu art Hwy near the Snake Ck.

crossing

5 Low lying area nil

behind school oval

6 Pooling in levee banks nil of Adelaide River

under the bamboo.

7 Swamp adjacent to the nil road leading into the

showgrounds.

8 Low lying area at nil

at the culvert 2km south of town.

0493GHXX.XLS

... .

STRICKLAND RD.

ADELAIDE R,

HWY.

•

• ADULT TRAP

*

LARVAL SAMPLE SITE

FIGURE l:ADELAIElE RIVER ADULT TRAP SITES AND LARVAL SAMPLE SITES.

FIGURE -2; ADELAIDE RIVER SEWAGE PONDS

Outlet

Mosquito breeding in first 60m of drain. Drain covered with vegetation. 2nd - 4th

instar larvae 100/dip. See photo 6.

Mosquito breeding in concrete

/

drain behind outlet. 200-300/dip.

2nd-4th instars. See photo 5.

POND 3: EVAPORATION POND Sloping concrete sides.

water level below concrete edges. Vegetation growth abundant. Cx. annulirostris breeding in high numbers around perimeter.

See photos 3-4.

20-30/dip lst&2nd instar larvae.

POND 2:SECONDARY POND Sloping concrete sides.

Some vegetation at ~ides.

No mosquito breeding.

See photo 2.

POND l: PRIMARY POND Straight concrete sides clear of vegetation.

No mosquito breeding~

See photo 1.

I '

30-50/dip lst&2nd ins~ars

I

80-100/dip

1st-4th & pupae

N

t

SCALE lCM

=

10 METRES ...

,

.

~J~UBE_l:

PRQrQ§~D FUTURE SUBDIVISIONS_ IN THE ADELAIDE RIVER TOWNSHIP

FIGURE 4

40 -

35

R 30 A

I

N F A 20 L L 15

M M 10

5 0

0496GHXX.XLC

' t

RAINFALL (MM) FOR THE BATCHELOR AREA FEBRUARY 1993

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

FEBRUARY

ooG:+:GS

/12..

A P P E N D I X 1.

MOSQUITO BREEDING AND SEWAGE TREATMENT

INTHE

NORTHERN TERRITORY

Peter I Whelan

Reprinted from 'Water' Journal of the Australian Water and Wastewater Association

Vol

15

No

5

Dec

1988

PP34-37

These pages have been removed as they

contravene copyright legislation.

Pages 19 to 22 of 23

APPENDIX 1

Title: Mosquito Breeding and Sewage Treatment in the Northern Territory

Author: Peter I Whelan Source: ‘Water’

Journal of the Australian Water and Waste Water Association

Volume 15, No. 5, Pages 34-37

December 1988

' •