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Northern Territory Department of Health Library Services Historical Collection
DL HIST
595.772
MON1993
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'111(€
DEPARTMENT OF HEAL TH~ AND COMMUNITY SERVICES
MOSQUITO SURVEY OF KATHERINE MEATWORKS AREA
29 -30 APRIL 1993
For more information contact:
NT Department of Health and Community Services Medical Entomology Branch P0Box40596
CASUARINA NT 0811 Telephone: 22 8333
Peter Whelan
Senior Medical Entomologist
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HISTORICAL COLLECTION
MOSQUITO SURVEY OF KATHERINE MEATWO.RKS AREA 29-30 APRIL 1993
Brian L. Montgome1·y Medical Entomologist Peter Whelan
Senior Medical Entomologist
DEPARTMENT OF HEALTH AND COMMUNITY SERVICES
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INTRODUCTION
Recent monitoring of adult mosquitoes at the Katherine meatworks indicated that numbers of the common banded mosquito Culex annulirostris were persistently high. An on-site survey was conducted on 29-30 April to determine the source of breeding as Katherine remains susceptible to a variety of mosquito-borne diseases.
There have been two previous investigations of mosquito problems concerning the Katherine meatworks and the resultant reports "Mosquito Investigations Katherine 13-14 September 1988" and "Mosquito Investigations of Katherine Meatworks 20-22 February 1989" included recommendations for rectifying specific mosquito breeding sites.
The location and rectification of these residual sources of mosquito breeding is necessary to prevent their transformation into major breeding sites once the meatworks resume dry season operations. The current survey was carried out by the use of adult mosquito traps at the meatworks and a survey of potential larval breeding sites at the meatworks, sewage ponds, Katherine River and the Springvale Homestead tourist resort.
MATERIALS AND METHODS
Adult mosquitoes were caught by the use of
co
2 baited EVS type traps run overnight. The location of the 6 traps set around the meatworks are shown in Figure 1. Adults were subsequently identified in the Medical Entomology laboratory in Darwin.The larval breeding survey was conducted by an initial visual appraisal of suspected breeding sites and subsequent sampling with a standard
"dipper". Sites where samples were collected are shown in Fieure 1.
RESULTS
Adult trapping
In all traps Cx annulirostris and Anopheles amictus predominated (Table
1). T.he relative abundance of each varied from site to site. At traps 1 and 5 An. amict.us was the most abundant species whereas Cx annulirostris dominated the other traps. Trap 2 (near sewage ponds) and trap 4 produced the largest catches. This is consistent with the primary pond being the major source. Trap 5 was relatively low due to the concentration of cattle overnight near this site.
Only at the least productive site (trap 6) did a third species, the brown house mosquito ex quinquefasciatus, form a substantial proportion of the sample (35%).
Females of other mosquito species represented in samples included the floodwater Aedes mosquito Ae. normanensis, the common Australian Anopheline An. annulipes and Cx pullus.
2
Larval survey
(i) Sewage ponds
The treatment ponds were well maintained with concrete margins. The lack of scum on the water surface and absence of weeds on the pond margins indicated that any breeding was being controlled by natural predators. The large earth-sided formalised evaporative ponds were free of marginal vegetation or dry and not a source of breeding. The unformalised overflow area which had a lot of marginal vegetation was dry at the time of the survey.
(ii) Meatworks
The major source of mosquito breeding was one of the two primary effluent ponds (Fig. 1, site a). Very high numbers of larvae were present in all instars (200/dip) and a large area was involved. Pupae were also present. Superficially this site did not appear as a source of mosquito breeding due to the large amount of surface scum. However, close inspection revealed that
ex
annulirostris was breeding prolifically in the relatively clean water in the spaces formed between conglomerates of scum.Secondary sources of breeding of
ex
annulirostris and An. amictus were located in nearby depressions (sites b, c and d). Although containing high numbers of larvae (200/dip) the breeding in these depressions was relatively recent (2-3 weeks) and small in area.The use of a large mechanical sprinkler system on the property to irrigate the fields with sewage effluent was not producing a mosquito problem because any pooling was temporary. The re-use of sewage in this way is a very effective waste water management strategy.
(iii) Katherine River
An inspection of the river north of trap 4 revealed that it was flowing freely and all levees were dry. The absence of marginal or isolated pools along the banks indicated that the river was not an appreciable source of mosquitoes.
(iv) Springvale
The billabong at Springvale Homestead annulirostris ( 1 larvae/dip) which is of tourists using the facility. There was indicating high nutrient levels and only presence of a hay bale in the billabong remains unknown.
DISCUSSION
contained low numbers of Cx minor but local importance to an algal scum on the surface, minor marginal vegetation. The was also noted but its purpose
The major mosquito breeding was occurring at the second primary pond in the meat works and could account for the majority of mosquitoes caught j n traps. Adults emerging from this area would harbor in the shelter of
3
trees along the riverbank during the day and feed on the cattle herd at night. Adult trapping indicated that ex quinquefasciatus breeding is occurring near the meatworks but the source remains undetected.
The rectification of mosquito breeding sites needs to be addressed in the short and long term.
(i) Sewage ponds
This site presents no problems in the short term. Weed cleaning and formalisation, particularly at the western end of the unformalised overflow area, is recommended to prevent breeding in this large area due to wet season flooding.
(ii) Meatworks
The large scale breeding at site (a) necessitated immediate control by the owners with larvicide (B.t.i. or Abate).
Short term rectification measures may necessitate the cleaning out of the sludge which has greatly reduced the holding capacity of this pond. In addition all weeds (Sesbania) on the effluent pond banks should be cleared prior to the resumption of the meat.works operations. Otherwise they create refuges from which larvae can escape predation as the water level rises.
Breeding areas in nearby depressions (site b and d) could be rectified by either filling or draining. Until then, weekly monitoring and control with
B.t.i. (Skeet.al) when necessary is recommended.
Site (c), a semi-permanent body of water, could be rectified in the long term by a drainage system to the river to drain excess water. If' th.is is not feasible its formalisation by excavation to form a pond with vertical sides and a defined margin would alleviate the problem.
(iii) Springvale
It is recommended that tests of water quality be conducted on the two springs that feed the billabong, and the billabong itself, to determine the level a.nd source of nutrients into the billabong. High nutrient levels may be due to contamination from the septic tanks nearby and this could possibly be investigated by the environment.al health officer. In addition the bale of hay in the billabong should be removed as soon as possible as it will add to the organic levels in the billabong.
All the above recommendations for control and rectification were discussed with the Katherine environmental health officer.
Brian L. Montgomery Medical Entomologist Peter Whelan
Senior Medical Entomologist
11 May 1993
4
5
TABLE 1. Numbers of mosquitoes caught in EVS type CO 2 baited adult mosquito traps at Katherine meatworks (29-30 April 1993).
TRAP An. amictus
ex
annulirostris Other Total1 126 58 10 194
2 178 282 4 461
3 46 189 3 238
4 91 306 20 417
5 96 89 8 193
6 32 23 33 88
'
FIGURE 1. Katherine Meatworks and surrounds
LEGEND
Pr<OPOSED SU8DIV1Sro'N noA'bs·
/\SSU'AEO CATCHMENT BOUNDARY
NATURAL OR ARTIFICIAL DRAINAGE CHANNEL
~~~
NATURAL nETARDING BASIN SHOWING 20YR INUNDATION! J - - O - Pr!OPOSED DRAINAGE CHANNEL
•
(a) SAMPLES OF LARVAE TAKEN FROM POSITION OF ADULT TRAPS
'
'SCALE
BREEDING S I ; t
/
0 100 2CX) 400 600 BOO 1000
