Medical Entomology Annual Report

2010/11

Medical Entomology Centre for Disease Control

Department of Health Northern Territory Government

September 2012

1 EXECUTIVE OVERVIEW

1.1 GOAL OF MEDICAL ENTOMOLOGY To reduce the impact of insects and other arthropods of medical importance on the health of the people of the Northern Territory.

1.2 VISION OF MEDICAL ENTOMOLOGY Every major urban area in the Northern Territory located in an environment that is planned, modified or controlled so that residents are not subjected to pest levels of biting insects and are free from the risks of both exotic or endemic mosquito borne disease.

1.3 MEDICAL ENTOMOLOGY SERVICES Services provided by Medical Entomology (ME) aim to reduce the impact of biting insects on the people of the Northern Territory (NT). These include the prevention of the re-introduction of malaria, the prevention of the introduction of exotic mosquito vectors of dengue, insecticide and engineering programs for mosquito control, mosquito surveillance programs in the major towns, guidelines and advice on biting insects for both large and small scale developments, a public inquiry service, a public awareness program, and incidental research on biting insects and mosquito borne viruses.

Major clients are the general public, but significant clients include local government, the Department for Planning & Infrastructure (DPI), the Department of Primary Industries, Fisheries & Mines (DPIFM), the Parks & Wildlife Services of the Northern Territory (PWSNT), Department of Defence, consultants and developers for development and planning advice, and environmental health officers.

Intersectoral affiliations include: a major involvement with the Darwin City Council in a combined mosquito engineering program in Darwin, with a $332225.85 budget this year for maintaining drains and rectifying urban or near urban mosquito breeding sites; the PWSNT in rectifying mosquito breeding sites and carrying out mosquito control in the Casuarina Coastal Reserve and the Botanic Gardens, and local government and Environmental Health Officers in the various towns throughout the NT on mosquito surveillance and mosquito control.

1.4 OBJECTIVES OF MEDICAL ENTOMOLOGY 1. Prevent the re-establishment of malaria by entomologically investigating and

appropriately responding to each case of imported malaria in the NT. Eliminate sources of malaria vectors near urban Darwin by engineering means.

2. Prevent the introduction of exotic dengue vector mosquitoes from overseas and Queensland by providing appropriate advice and assistance to Quarantine authorities, active surveillance using special egg traps, regular surveys for larvae at vulnerable geographic points of introduction, reduction of potential breeding places by landowner liaison and media advertising, and eradication procedures after detection of importation.

3. Carry out surveillance and control of mosquitoes in all major towns and mine developments by organising and assisting with regular mosquito trapping and providing advice and assistance with control operations, under the NT Mosquito Borne Disease Control program and a User Pays Scheme.

4. Carry out mosquito surveys throughout the NT, including remote communities, to determine the distribution and relative abundance of mosquitoes in order to enable the assessment of the risk of mosquito borne disease.

5. Carry out extensive and intensive mosquito larval control operations in Darwin

using a helicopter applied insecticide program in the coastal swamps.

6. Organise and assist the Darwin City Council and the PWSNT with engineering

programs in and adjacent to urban areas, under the combined Mosquito Engineering Control Program.

7. Carry out surveillance of flaviviruses causing human disease by: maintaining a sentinel chicken surveillance program with the assistance of DPIFM and volunteers, the investigation of outbreaks of mosquito borne disease, and the collection and processing of mosquitoes for arbovirus isolation.

8. Provide planning and development advice and guidelines to DLP and others to prevent new biting insect problems for various minor and major development projects.

9. Promote public awareness on biting insects and arthropod borne disease by regular public communication, a public reference service, the promotion of the Mosquito Control Advisory Committee, preparation of public information sheets, an internet site for advice and high quality information pamphlets and publications.

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10. Assist students and other bodies in basic research on biting insects and other arthropods of medical importance.

11. Carry out incidental and applied research both independently or in cooperation with other researchers on biting insects in the NT to establish improved methods for the avoidance, reduction or control of insects of public health importance.

12. Build and maintain a reference collection of mosquitoes, biting midges and other arthropods of medical importance in the NT.

13. Provide opportunities for staff development by in-service and external training, so that they are better able to deliver services.

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1.5 PERFORMANCE FOR 2010 – 2011 There were 3 exotic mosquito importations through sea ports in the NT this year

compared to 4 detections last year. In each instance, surveillance and elimination responses were carried out by ME and the Australian Quarantine Inspection Service (AQIS) until no further detections were made.

Between August 2010 and June 2011 ME carried out a number of vector surveys

in population centres within the Darwin region outside Darwin and verified the absence of the dengue mosquito Aedes aegypti in these areas.

There were 190 Ross River virus (RRV) and 45 Barmah Forest virus (BFV)

disease cases in the Darwin region this year compared to 234 RRV and 70 BFV cases in 2009/10. In the whole of the NT there were 262 RRV cases this year compared to 320 last year and 410 in 2008/09, with an appreciable decreased number of cases in the Darwin, East Arnhem and Alice Springs regions. In the Katherine and Barkley regions the same number of cases occurred as last year.

This year the area requiring treatment under the ME aerial mosquito control program in tidal influenced swamps near Darwin was notably higher, with 2119 hectares sprayed in the combined Leanyer, Holmes Jungle, Micket Creek and Shoal Bay swamps compared to last year (1080 ha). This was primarily due to more control operations required between July and September 2010 for Aedes vigilax, the northern salt marsh mosquito after high tides that were higher than the previous year. Due to the control efforts, numbers of Ae. vigilax were markedly lower, with an average per trap per night from the eleven continuous once weekly set Darwin traps of 154.56 compared to 215.73 last year.

One of the most important ongoing issues is the lack of a comprehensive mosquito survey and control operation for Palmerston and the rural area. This is becoming increasingly relevant as the population of Palmerston increases and more people are placed close to uncontrolled mosquito breeding sites. This problem will need resolution by the managers of Crown Land, the Palmerston City Council, the Litchfield Shire Council and DoH.

The 11 NT sentinel chicken flocks were bled a total of 117 times for flavi-virus antibody testing. The Leanyer (Darwin), Coastal Plains Research Station, Tennant Creek and Alice Springs flocks showed evidence of Murray Valley encephalitis virus, while the Howard Springs, Leanyer, Coastal Plains Research Station, Jabiru, Nhulunbuy, Katherine and Tennant Creek flocks showed evidence of Kunjin virus. There were 4 cases of Murray Valley encephalitis virus disease contracted in the NT, with 2 cases in the Barkly region in March and April 2011, and 2 cases in the Top End (Katherine/Darwin regions) in May.

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There were 17 cases of imported malaria into the NT, one of which required entomological investigations and a subsequent fogging operation, as the case posed a risk of local Anopheles mosquitoes becoming infected.

ME continued with investigations associated with the proposed new city of

Weddell, with trap results revealing high to very high pest mangrove biting midge (Culicoides ornatus) abundance in all areas of Weddell within 1.5km of the mangrove margin of the Elizabeth and Blackmore Rivers, supporting the previous years trapping results. The greatest biting midge abundance was located in the north-west portion of Weddell. Investigations also revealed much of Weddell is subject to seasonally high to very high northern salt marsh mosquito (Aedes vigilax) numbers.

ME published eleven scientific papers. Six of these papers were part of the ARC

Linkage Project. ME also produced five branch reports, including the ME Annual Report, and contributed to the Communicable Disease Network Australia annual arbovirus report.

ME produced calendars showing pest periods for the mangrove biting midge

Culicoides ornatus and the northern salt marsh mosquito Ae. vigilax for the coastal Top End of the NT for the 2011 calendar year.

ME processed 6822 mosquitoes for virus isolation from Howard Springs,

Borroloola and the Katherine. No virus was isolated from the Howard Springs, Borroloola or Katherine mosquitoes.

In May 2011, an unknown mosquito was collected in a routine Darwin adult

monitoring trap set near Marrara swamp and was tentatively identified as Culex cornutus. Further investigations will be carried out in 2012 to verify the Culex species present.

2 INTRODUCTION TO 2010 – 2011 ANNUAL REPORT

The Medical Entomology Annual Report 2010/11 is intended to present an overall picture of DoH mosquito surveillance and control activities carried out in the Northern Territory in 2010/11.

The Medical Entomology Annual Report 2010/11 is also available electronically on the DoH internet site:

http://www.health.nt.gov.au/Medical_Entomology/index.aspx

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http://www.health.nt.gov.au/Medical_Entomology/index.aspx

CONTENTS

1 EXECUTIVE OVERVIEW 1 1.1 GOAL OF MEDICAL ENTOMOLOGY 1 1.2 VISION OF MEDICAL ENTOMOLOGY 1 1.3 MEDICAL ENTOMOLOGY SERVICES 1 1.4 OBJECTIVES OF MEDICAL ENTOMOLOGY 2 1.5 PERFORMANCE FOR 2010 – 2011 4 2 INTRODUCTION TO 2010 – 2011 ANNUAL REPORT 5 3 EXOTIC VECTOR SURVEILLANCE 14 3.1 Introduction 14 3.2 Aedes Ovitrap Surveillance Program 14 3.2.1 Darwin City and Outer Darwin 15 3.2.2 Darwin Rural and Palmerston 16 3.2.3 Groote Eylandt - Alyangula 16 3.2.4 Nhulunbuy 16 3.2.5 Katherine 17 3.2.6 Tennant Creek 17 3.2.7 Alice Springs 17 3.3 AQIS Adult Mosquito Trapping Program 18 3.3.1 Darwin 18 3.4 Exotic Mosquito Interceptions 18 3.5 Receptacle Breeding Surveys 19 4 VECTOR SURVEILLANCE & CONTROL IN THE NORTHERN

TERRITORY 20 4.1 Darwin 20 4.1.1 Adult Mosquito Monitoring Program 21 4.1.2 Vectors & Disease case data 24 4.1.3 Routine Ground Larval Mosquito Control Program Darwin 25 4.1.4 Aerial Mosquito Control Program 28 4.1.5 Mosquito Engineering Control Program 28 4.1.6 Suggestions for improved vector surveillance and control 29 4.2 Ranger Mine 31 4.2.1 Monitoring program 31 4.3 McArthur River Mine 32 4.4 Groote Eylandt 33 4.4.1 Mosquito species recorded in Groote Eylandt 33 4.4.2 Adult Mosquito Monitoring Program 33 4.4.3 Vector & Disease case data 34 4.4.4 Suggestions for improved vector surveillance and control 35 4.5 Nhulunbuy 36

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8 PLANNING AND DEVELOPMENT INVESTIGATIONS AND COMMENTS 54 8.1 Development comments 54 8.2 Development investigations 54 8.2.1 Weddell – supplementary investigation 2010 54 8.2.2 Weddell – biting insect trapping 2010/11 55 8.2.3 East Arm Port Expansion biting insect assessment 55 9 MOSQUITO FIELD SURVEYS IN THE NORTHERN TERRITORY 56 10 MOSQUITO AWARENESS AND TRAINING 56 10.1 Mosquito awareness campaign 56 10.2 ME training 56 11 PUBLIC ENQUIRIES 56 12 COMMITTEES AND ADVISORY GROUPS 57 12.1 National Arbovirus Advisory Committee 57 12.2 North Australian Health Ministers Vector Working Group 57 12.3 Technical Advisory Group – Aedes albopictus Eradication Program Torres

Strait 57 13 PUBLICATIONS AND PAPERS 58 14 REFERENCE COLLECTIONS 58 15 DATA MANAGEMENT 59 15.1 Medical Entomology Data Collection System 59 15.2 Geographic Information Systems 59 16 STAFF MATTERS 59 17 REFERENCES 60 18 ACKNOWLEDGEMENTS 61

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FIGURES 1 – 23 Fig. 1. Darwin Adult Mosquito Monitoring Program. Location Of

Weekly Adult Mosquito CO2 Baited Trap Sites. Fig. 2. Darwin Urban Ovitrap Monitoring Program. Location Of Ovitrap

Sites And Sentinel Chicken Sites. Fig. 2. Darwin Rural Ovitrap Monitoring Program. Location of Ovitrap

Sites And Sentinel Chicken Sites. Fig. 4. Alyangula Adult Mosquito Monitoring CO2 Trap Site, Sentinel

Chicken And Ovitrap Locations. Fig. 5. Angurugu Adult Mosquito Monitoring CO2 Trap Site And

Ovitrap Locations . Fig. 6. Nhulunbuy Adult Mosquito Monitoring CO2 Trap Sites, Ovitrap

Locations And Sentinel Chicken Locations. Fig. 7. Katherine Adult Mosquito Monitoring CO2 Trap Sites, Sentinel

Chicken And Ovitrap Locations. Fig. 8. Tennant Creek Adult Mosquito Monitoring CO2 Trap Sites,

Ovitrap And Larval Sites And Sentinel Chicken Flock Locations. Fig. 9. Alice Springs Adult Mosquito Monitoring CO2 Trap Sites,

Sentinel Chicken And Ovitrap Locations. Fig. 10. AQIS Darwin Adult Mosquito Monitoring Program. Fig. 11. Aedes aegypti Ovitrap Surveillance Program – Darwin City And

Outer Darwin 2010/11. Total Number Of Larvae In All Thirty seven Trap Sites; Rainfall At Darwin Airport.

Fig. 12. Aedes aegypti Ovitrap Surveillance Program – Darwin Rural And Palmerston 2010/11. Total Number Of Larvae In All Thirteen Trap Sites; Rainfall At Darwin Airport.

Fig. 13. Mosquito Monitoring Program Darwin. Average Number Of Aedes notoscriptus, Aedes vigilax, Culex annulirostris Group, And All Species Trapped Per Trap Night Per Year For The Eleven Continuous Monitoring Sites And Annual Rainfall In Darwin – 1983/84 To 2010/11.

Fig. 14. Mosquito Monitoring Program Darwin. Average Number Of All Female Mosquitoes Per Trap Night Caught Using Weekly CO2 Baited Mosquito Traps At The Eleven Continuous Monitoring Sites, 2006/07 To 2010/11.

Fig. 15. Monthly Rainfall And Monthly Ross River Virus Disease Cases For Towns of The Northern Territory From July 1996 – June 2011. RRV Disease Cases From CDC, Darwin. Rainfall Data From Bureau Of Meteorology.

Fig. 16. Monthly Rainfall And Monthly Average Number Of Cx. annulirostris Grp. (Average Per Trap Night, CO2 Baited Traps) For Towns Of The Northern Territory From July 1996 – June 2011. Rainfall Data From Bureau Of Meteorology.

Fig. 17. Darwin. Total Monthly Rainfall In Relation To Ae. Notoscriptus, Ae. vigilax, Cx. annulirostris Grp. & Ve. Funerea July 1991 To June 2011.

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Fig. 18. Darwin. Monthly RRV Disease Cases In Relation To Ae. notoscriptus, Ae. vigilax, Cx. annulirostris & Ve. funerea July 1991 To June 2011.

Fig. 19. Aerial Applied Mosquito Larval Control Program Major Mosquito Breeding Areas – Darwin.

Fig. 20. Ross River Virus Disease Cases In The NT. Laboratory Confirmed Cases From CDC (By Month Of Report) 1998/99 To 2010/11.

Fig. 21. Location Of Sentinel Chicken Flocks In The NT. Fig. 22. Northern Territory Rainfall Deciles 1 July 2010 To 30 June 2011. Fig. 23. Northern Territory Rainfall Totals (MM) 1 July 2010 To 30 June

2011.

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Tables 1 - 41 Table 1. Aedes aegypti Ovitrap Surveillance Program - Darwin City And

Outer Darwin. July 2010 - June 2011. Table 2. Aedes aegypti Ovitrap Surveillance Program – Darwin Rural And

Palmerston. July 2010 – June 2011. Table 3. Adult Mosquito Species List Darwin. Table 4. Mosquito Monitoring Program Darwin July 2010 To June 2011.

Total Numbers Of Nine Selected Species Of Female Mosquitoes Caught In Eleven Continuous Weekly CO2 Baited Mosquito Traps.

Table 5. Mosquito Monitoring Program Darwin July 2010 To June 2011. Total Number Of Nine Selected Species Of Female Mosquitoes Caught In All 22 Weekly CO2 Baited Mosquito Traps.

Table 6. Mosquito Monitoring Program Darwin. Average Numbers Of Nine Selected Species Caught In The Eleven Continuous Weekly CO2 Baited Mosquito Traps For The Financial Years 1990/91 To 2010/11.

Table 7. Ross River Virus Disease Cases In The NT Laboratory Confirmed Cases Notified From CDC (By Region Per Month) July 2010 To June 2011.

Table 8. Barmah Forest Virus Disease Cases In The NT Laboratory Confirmed Cases Notified From CDC (By Region Per Month) July 2010 To June 2011.

Table 9. Ross River Virus Disease Cases In The NT. Laboratory Confirmed Cases Notified From CDC (By Region) 1990/91 To 2010/11.

Table 10. Barmah Forest Virus Disease Cases In The NT. Laboratory Confirmed Cases Notified From CDC (By Region) 1991/92 To 2010/11.

Table 11. Location And Month Of Onset Of Cases Of MVE Or KUN 1974 – 2011 Acquired In The NT.

Table 12. Arbovirus Risk Periods In The Northern Territory. Table 13. Combined DoH And DPIFM NT Sentinel Chicken Flavi Virus

Surveillance. Progressive Results Of Number Of New Seroconversions In Month Of Bleeding 2010/11.

Table 14. Combined DoH And DPIFM NT Sentinel Chicken Flavi Virus Surveillance. Summary Of New Seroconversions By Month Jul 1992 – Jun 2011.

Table 15. Combined DoH And DPIFM NT Sentinel Chicken Flavi Virus Surveillance. New Seroconversions In Month Of Bleeding By Year Jul 1992 – Jun 2011.

Table 16. Adult Mosquito Species List Gove Peninsular. Table 17. Mosquito Monitoring Program Nhulunbuy. Numbers Of Selected

Species Of female Mosquitoes Caught In The Six Weekly Co2 Baited Mosquito Traps 1 July 2010 To 30 June 2011.

Table 18. Mosquito Monitoring Program Nhulunbuy. Average Numbers Of Selected Species Caught In The Five Continuous Weekly CO2 Baited Mosquito Traps For Financial Years 1994/95 To 2010/11.

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Table 19. Mosquito Monitoring Program Nhulunbuy. Total Numbers Of Selected Species Of Female Mosquitoes Caught In All Co2 Baited Mosquito Traps 1990/91 To 2010/11.

Table 20. Adult Mosquito Species List Groote Eylandt. Table 21 . Mosquito Monitoring Program Alyangula. Total Numbers Of

Selected Species Of Female Mosquitoes Caught In All CO2 Baited Mosquito Traps 1 July 2010 To 30 June 2011.

Table 22. Mosquito Monitoring Program Alyangula. Average Numbers Of Selected Species Of Female Mosquitoes Caught In The CO2 Baited Mosquito Traps For Financial Years 1995/96 To 2010/11.

Table 23. Mosquito Monitoring Program Alyangula. Total Number Of Female Mosquitoes Caught In All CO2 Baited Mosquito Traps 1 July 1995 To 30 June 2011.

Table 24. Adult Mosquito Species List Katherine Town. Table 25. Mosquito Monitoring Program Katherine. Total Numbers Of

Selected Species Of Female Mosquitoes Caught In The Five CO2 Baited Mosquito Traps 1 July 2010 To 30 June 2011.

Table 26. Mosquito Monitoring Program Katherine. Average Number Of Selected Species Caught In The 3 Weekly CO2 Baited Mosquito Traps For Financial Years 1990/91 To 2010/11.

Table 27. Mosquito Monitoring Program Katherine. Total Numbers Of Female Mosquitoes Caught In All CO2 Baited Mosquito Traps For Financial Years 1990/91 To 2010/11.

Table 28. Adult Mosquito Species List Tennant Creek. Table 29. Mosquito Monitoring Program Tennant Creek. Total Number Of

Selected Species Of Female Mosquitoes Caught In All Weekly CO2 Baited Traps 1 July 2010 To 30 June 2011.

Table 30. Mosquito Monitoring Program Tennant Creek. Average Number Of Selected Species Of Female Mosquitoes Caught In The Continuous Weekly CO2 Baited Traps For Financial Years 1990/91 To 2010/11.

Table 31. Mosquito Monitoring Program Tennant Creek. Total Number Of Female Mosquitoes Caught In All Weekly CO2 Baited Traps For Financial Years 1990/91 To 2010/11.

Table 32. Adult Mosquito Species List Alice Springs. Table 33. Mosquito Monitoring Program Alice Springs. Total Number Of

Selected Species Of Female Mosquitoes Caught In All Weekly CO2 Baited Traps 1 July 2010 To 30 June 2011.

Table 34. Mosquito Monitoring Program Alice Springs. Average Number Of Selected Species Caught In The Continuous Weekly CO2 Baited Mosquito Traps For Financial Years 1990/91 To 2010/11.

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Table 35. Mosquito Monitoring Program Alice Springs. Total Number Of Selected Species Caught In All Weekly CO2 Baited Traps For Financial Years 1990/91 To 2010/11.

Table 36. AQIS Exotic Mosquito Monitoring Program - Darwin. 1July 2010 To 30 June 2011. Total Number Of Female Mosquitoes Caught In All CO2 Baited EVS Traps.

Table 37. AQIS Exotic Mosquito Monitoring Program - Darwin. 1July 2010 To 30 June 2011. Total Number Of Female Mosquitoes Caught In All CO2 Baited Biogents Sentinel MosquitoTraps.

Table 38. Malaria Notifications In The Northern Territory 1 July 2010 To 30 June 2011.

Table 39. Interception Of Exotic Mosquitoes in Northern Territory Seaports July 2000 - June 2011.

Table 40. Medical Entomology Survey And Travel July 2010 To June 2011. Table 41. Medical Entomology Publications 2010/11.

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3 EXOTIC VECTOR SURVEILLANCE

3.1 Introduction The most frequently intercepted exotic mosquitoes in the NT are the dengue mosquito, Aedes aegypti, and the Asian tiger mosquito, Aedes albopictus. These dengue and chikungunya vectors can be transported as eggs or larvae in actual or previously water-filled receptacles on ships and cargo arriving from foreign ports, or as desiccant resistant eggs on receptacles relocated from areas in north Queensland (Qld) where they are either endemic (the former), or recently established in the Torres Strait (the latter).

There have been two instances since the elimination in late 1950’s where the exotic mosquito Ae. aegypti was found as established populations in the NT. These establishments were discovered through surveillance detections in Tennant Creek in 2004 (through the adult mosquito surveillance program) and in Alyangula in 2006 (through the ovitrap surveillance program). In both instances, the populations were eliminated after two year programs by DoH, with funding assistance from the Commonwealth Department of Health and Ageing.

At present, local periodic transmission of dengue in Australia is restricted to Qld where Ae. aegypti occurs. Transmission occurs when the viruses are introduced by infected overseas travellers. Aedes aegypti is geographically widespread in north and outback Qld, but the NT remains dengue vector free.

The NT has an appreciable public health and economic benefit by preventing the dengue vectors and other exotic vectors of disease from becoming established. ME has routine and ongoing exotic mosquito monitoring and exclusion programs around all major towns and entry points to prevent the introduction or establishment of dengue vectors, and conducts periodic surveys of other towns and localities to ensure the NT remains dengue vector free.

3.2 Aedes Ovitrap Surveillance Program The exotic Aedes ovitrap (egg trap) surveillance program is a continual routine program used to detect any importations of exotic Aedes mosquito species into the NT, and thus allows timely control or elimination measures. In 2010/11 there were 37 ovitraps in the Darwin area (Table 1, Fig. 2) and 13 ovitraps in the Palmerston and rural areas (Table 2, Fig. 3) that were collected, inspected, and re-set fortnightly. The regional ovitrap programs in Gove, Alyangula, Tennant Creek, Katherine and Alice Springs are also inspected and re-set fortnightly. The Darwin ovitraps are set and retrieved by ME, while the ovitraps in the regional centres are set and retrieved by Environmental Health Officers (EHO) and local land corporation or mine site personnel.

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Ovitraps are located in most suburbs of Darwin and in various rural residential areas. They are also set adjacent to vulnerable entry points for exotic mosquito incursions from overseas or Qld. Vulnerable entry points include port areas, interstate trucking yards, removalist companies, caravan parks, tyre yards and plant nurseries.

Ovitrap paddles from all regions except Darwin are received by ME, along with any larvae found in the traps. The eggs on the paddles are hatched in the ME laboratory and all larvae are reared through to fourth instars for identification to species level. When exotics or the endemic species Ae. katherinensis are suspected to be present, the larvae are reared through to the adult stage for identification as the exotic species Ae. albopictus larvae appear very similar to Ae. katherinensis larvae.

The number of mosquito eggs laid on ovitrap paddles is generally dependant on the abundance of the adult (female) population, and in turn can relate to the productivity, number, and proximity of suitable breeding sites where the ovitrap is located. The seasonal pattern of larval numbers (eggs laid) from ovitraps is ultimately dependant on the extent and frequency of rainfall in the wet season or the artificial filling of receptacles during the dry season due to garden irrigation.

The ovitrap programs undergo a continual reassessment throughout the year to increase the efficiency of the program. Ovitrap site placements are adjusted according to changed conditions and risk levels, such as loss of vegetation cover overhead, changes in property ownership, access issues, the arrival of risk cargo imported from locations where the target mosquitoes are prevalent, and when there are detections of adult mosquitoes from quarantine collections.

Given that the exotic disease vectors Ae. aegypti and Ae. albopictus can potentially utilise the same breeding habitats as the endemic Aedes species, the recovery of endemic receptacle breeding Aedes in a vulnerable location, such as the port areas is an indicator of available breeding sites for exotic Aedes. The recovery of appreciable numbers of endemic Aedes species in the ovitraps are an indication that ongoing awareness campaigns aimed at household and commercial premises with regards to receptacle-breeding mosquitoes need to continue.

3.2.1 Darwin City and Outer Darwin In Darwin, of all ovitraps samples (902), 28.71% (259) were positive for mosquito larvae (Table 1). This percentage of positive ovitraps is similar compared to last year (34.59% positive). There was an initial reduction in the presence of Ae. notoscriptus in ovitraps in July – August and one major peak before the first major rainfall event in September. This is likely due to an initial reduction in the population of the species due to the presence of fewer alternate nearby breeding sites, followed by later remaining ovitraps becoming one of the few receptacles available for egg laying females (Fig. 11). With the increase in rainfall at the start of the wet season rains in October the number of Ae. notoscriptus collected in the ovitraps decreased due to the availability of alternative breeding sites (Fig. 11).

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The species most often detected in all traps was Ae. notoscriptus (246 times, present in 94.98 % of positive ovitraps), followed by Ae. tremulus (13 times, present in 5.02% of positive ovitraps) (Table 1).

Up to 47.15 % of ovitraps collected from residential premises were positive for mosquito eggs. The next highest were transport companies with 25.93%, port areas (11.69%), caravan parks (11.11%) and commercial companies (2.80%) (Table1).

3.2.2 Darwin Rural and Palmerston In 2010/11, 28.57% (98) of ovitraps sampled (343) in Darwin rural and Palmerston were positive for mosquito larvae (Table 2, Fig. 12) compared to 34.59% in 2009/10. The species most often detected was Ae. notoscriptus (95 times, present in 96.94% of positive ovitraps) followed by Ae. tremulus (15 times, present in 15.31% of positive ovitraps) (Table 2).

In the Darwin rural and Palmerston ovitraps, Ae. notoscriptus abundance increased with the onset of rainfall in October and slightly decreased with the increase in rainfall in December (Fig. 12). An initial increase in Ae. notoscriptus in the ovitraps is likely due to increases in the adult female mosquito population with early wet season rains.

3.2.3 Groote Eylandt - Alyangula Alyangula is a mining town located on Groote Eylandt in the Gulf of Carpentaria in the East Arnhem region. Many of the legal vessel arrivals are for ore export or coastal cargo transport barges to and from Darwin. There is also a possibility of illegal vessels landing on Groote or nearby areas. As with Nhulunbuy, the port area is considered a vulnerable entry point for exotic Aedes species into the NT from Qld and overseas.

The ovitrap program operates in collaboration between the Groote Eylandt Mining Company (GEMCO) and ME. The ovitrap program was established in July 1998 and continued to March 2000, when local staff shortages resulted in its suspension. The program was re-established in March 2003. The five ovitraps are located at the wharf, the airport, mine site, and the Alyangula Township (Old and New Town) and are serviced fortnightly (Figs 4 and 5).

In 2010/11, Aedes notoscriptus, Ae. tremulus, Ae. katherinensis and Culex. quinquefasciatus were the endemic species collected. No exotic mosquitoes were detected in 2010/11.

3.2.4 Nhulunbuy Nhulunbuy is a mining town and the principal town in the East Arnhem region. The town is considered a vulnerable entry point for exotic Aedes species into the NT

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because of mining related transport arriving from overseas and Qld, as well as illegal foreign fishing vessels (IFFVs) being detained near Port Melville and prepared for onshore destruction at Drimmie Head by a local contractor. An ongoing ovitrap surveillance program was established in Nhulunbuy in 1995/96 in collaboration with the Nhulunbuy Corporation.

There are six routine ovitrap sites in Gove. These are located in the seaport areas, the township, the airport, the waste facility, and Catalina Beach Boat Yard (Fig. 6).

In 2010/11, no exotic mosquitoes were detected. The endemic species Aedes temulus, Cx. quinquefasciatus and Ae. notoscriptus were collected.

3.2.5 Katherine The ovitrap surveillance program in Katherine consists of eight routine ovitraps. The traps are located adjacent to vulnerable entry points into Katherine, including the railway terminal, tyre centres, the Cycad Garden Nursery and the fire station (Fig. 7).

The ovitraps are serviced by the Environmental Health Officer in Katherine each fortnight, and the paddles and any larvae are forwarded to ME for larval rearing and identification.

In 2010/11, no exotic mosquitoes were recovered from the Katherine ovitraps. The endemic species Aedes notoscriptus, Cx. quinquefasciatus, Ae. tremulus and Ae. katherinensis were collected.

3.2.6 Tennant Creek The Tennant Creek ovitrap surveillance program consists of three ovitraps set at the Memorial Club, 3 Kittle Street and the Caravan Park (Lot 2133) (Fig. 8). The traps are serviced fortnightly by the Tennant Creek EHO during the wet season only, commencing after the first appreciable rains.

In 2010/11, ovitraps were only set once in April 2011 due to the unavailability of the EHO.

3.2.7 Alice Springs The Alice Springs ovitrap surveillance program consists of seven ovitraps (Fig. 9).The ovitraps are serviced fortnightly by the Alice Springs Environmental Health Officer.

In 2010/11, only the endemic mosquitoes Ae. tremulus, Ae. notoscriptus and Cx. quinquefasciatus were recovered from the Alice Springs ovitraps.

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3.3 AQIS Adult Mosquito Trapping Program There were two Aedes aegypti and one Ae. albopictus adults detected in the BG trap set at the Perkins international wharf quarantine shed (Table 37).

3.3.1 Darwin In 1999, ME resumed the mosquito identifications of the AQIS adult mosquito trapping program samples as a cost per service program. The aim of the program is to monitor for exotic adult mosquitoes around the Darwin port and airport areas. Weekly routine adult mosquito EVS trapping is conducted by AQIS at vulnerable entry points in these areas (Fig. 10, Table. 36).

In early 2010, Biogents sentinel adult mosquito traps (BG), specifically designed to attract and collect Ae. aegypti and other Aedes (Stg) species, such as the exotic Ae. albopictus and the endemic Ae. katherinensis, were incorporated into the quarantine monitoring program (Fig. 10, Table 37). Carbon dioxide gas was used to enhance the attractiveness of the traps (Meeraus et al 2008).

The six CO2 baited EVS traps and the four BG traps are set and collected weekly by the AQIS Vector Officers and the mosquitoes are forwarded to ME for identification. Once identified, the results are forwarded to AQIS Vector Officers, the RAAF and Darwin Airport, Perkins Shipping Environmental and Safety Officers, and the Darwin Port Authority.

The six routine AQIS EVS monitoring trap sites in Darwin are located at Fort Hill Wharf, Perkins Shipping, Darwin Airport, East Arm Wharf, and two traps at the RAAF Base (Military Hard Stand (MHS) and the Fighter replenishment Apron (FRA) (Fig. 10).

There were no exotic mosquitoes recovered in the EVS traps in 2010/11 (Table 36). However, Aedes aegypti was detected on 4th January 2011 and Ae. albopictus on 10th March 2011 from a BG trap set in the Perkins Shipping international wharf area (Table 37). In both instances, surveillance and elimination responses were carried out by ME and AQIS until no further detections were made.

3.4 Exotic Mosquito Interceptions In the NT, AQIS survey and treat apprehended IFFVs and illegal persons vessels for any exotic pest threats to Australia, including mosquitoes. Illegal vessels are usually detained and escorted to a port by the Royal Australian Navy and the Australian Custom Services. Some vessels, such as fishing iceboats traditionally carry large 800-1000L drinking water receptacles that are sealed and therefore are not suitable for mosquito breeding. Shark boats and illegal persons vessels however, often use open 200L plastic drums as drinking water receptacles, which are suitable for mosquito breeding, and exotic larvae are often detected in these receptacles.

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In 2010/11, information forwarded from AQIS indicated that there were no interceptions of exotic mosquitoes from IFFVs detained in NT ports (Table 39). Illegal vessels apprehended in NT waters are generally now diverted to Christmas Island where the fishers or illegal persons are processed and the vessels are destroyed. This is reflected in the decline of exotic mosquito interceptions from IFFVs from NT seaports in the recent data trend. There were 13 interceptions from IFFVs in 2001 reaching a high of 30 in 2002/03 then falling and remaining at low levels (one to two interceptions) from 2006/07 onwards.

Table 39 shows port of origin, vessel type and receptacle type for all exotic species recorded in Northern Territory seaports between 2000/01 and 2010/11.

Aedes aegypti has been the most frequently detected species from receptacles at seaports (105 instances out of 133 exotic species detections), with Ae. albopictus only collected 10 times out of the 138 detections since 2000/01 (Table 39).

Previous data showed that the potential importation of Ae. aegypti into the NT is more likely to be through IFFVs via water holding receptacles used for drinking water storage. Aedes albopictus appears more likely to be imported via used tyres and other receptacle types, which generally arrive on cargo vessels. Drinking water receptacles usually have less nutrients present in the form of leaf and insect detritus, and thus may be less attractive for egg laying Ae. albopictus.

In addition, Ae. aegypti is a highly domesticated species that primarily feeds on humans. The proximity of drinking water receptacles and humans at the port of IFFV origin would tend to increase the likelihood of Ae. aegypti presence and transportation via this mode. However, since apprehended IFFVs tend to be moored 1.5 nm from shore during quarantine inspection procedures for the majority of the times they are detained, the higher risk of importations within the Darwin port environs would appear to be via international cargo vessels. The risks of exotic importations into areas other than first ports of call would be from illegal shore landings of IFFV or other illegal vessels.

3.5 Receptacle Breeding Surveys As part of the ME exotic vector surveillance program, surveys for receptacle breeding exotic Aedes mosquitoes are conducted as a supplement to the ovitrap program. The aim is to detect exotic mosquito incursions that have breached the 400m quarantine zone at international ports or those arriving from Qld by road or via any other mode.

Locations that are targeted for the potential presence of exotic receptacle breeding species are port areas, nurseries, caravan parks and transport companies, as they are potential entry points for exotic mosquitoes in the NT. Some commercial and residential premises outside these categories are also surveyed, particularly those close to potential entry points listed above, or that contain a large number of potential receptacle breeding sites.

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Port areas receive international shipping traffic and are thus susceptible to potential exotic mosquito incursions. Caravan parks and transport companies represent a risk of interstate vehicles inadvertently transporting Ae. aegypti eggs or larvae in receptacles across the border from Queensland. Nurseries are considered a risk because they often import plants and pots from interstate (including Qld) and overseas, and they can contain suitable breeding or adult harbourage sites.

As shown by the Groote Eylandt Ae. aegypti incursion, remote coastal locations close to frequent IFFV activity are potentially subject to exotic mosquito introductions via routes other than through the main shipping ports. The method of introduction into nearby towns or communities may be via relocation of receptacles obtained from IFFV camps or via bartering between IFFV crew and local residents.

During the 2010/11 financial year, ME surveyed locations within the Darwin region (Dundee Beach and Snake Bay) and the Katherine region (McArthur River and Mataranka). Surveys carried out at Dundee Beach and Snake Bay were part of an investigation for a suspected dengue case. No exotic mosquitoes were found, and no further dengue cases were reported.

The majority of the Darwin port areas within the 400m quarantine zone were surveyed very early in the wet season as an AQIS/ME joint program. This timing allowed for the assessment of the receptivity of each port area before the main wet season so that source reduction recommendations could be conveyed to the respective proprietors, and actioned in a timely manner.

During the routine receptacles surveys, no exotic mosquitoes were detected in any of the locations mentioned above. However, during enhanced surveillance in response to exotic mosquito interceptions at the Darwin Port, Ae. aegypti and Ae. albopictus were found as mentioned in section 3.3.1. This indicates that the joint Aqis/ME program works well in preventing exotic mosquito establishments in the NT.

4 VECTOR SURVEILLANCE & CONTROL IN THE NORTHERN TERRITORY

4.1 Darwin The most important mosquito species recorded from routine CO2 baited EVS traps in Darwin in 2010/11 and their relative numbers are shown in Tables 3-6. There were 52 adult mosquito species collected in Darwin in 2010/11 (Table 3).

Two new mosquito species were recorded, Aedes (Mac) nr species 121, and the tentatively identified Cx. cornutus. Taxonomic keys have since been developed by Medical Entomology to incorporate Aedes (Mac) nr species 121. Further investigations will be carried out in 2011/12 to verify existing populations of Cx. cornutus.

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4.1.1 Adult Mosquito Monitoring Program 4.1.1.1 Monitoring program

The routine adult mosquito monitoring program in the Darwin area involved 22 CO2 baited EVS traps set throughout the Darwin urban area (Table 5, Fig. 1). Two new wet season trap sites were added at East Point and Fishermans Wharf, due to appreciable wet season mosquito breeding sites in these areas, and a need to determine the success of larval control in these areas. The Holmes Jungle trap site was shifted to Shoal Bay Dump, but due to low catches (the dump is a relatively open area) the trap was moved back to the Holmes Jungle area.

Eleven of the trap sites have been monitored continuously using the same trap type from 1985 to the present (Table 4). A few of these trap sites have been consistently monitored from 1979 to the present, representing one of the longest consistent adult mosquito monitoring data sets in Australia. This data is used to evaluate long term mosquito control and disease risk.

4.1.1.2 Adult mosquito numbers The financial year results for the 11 continuous traps are shown in Table 4. The results from all 22 trap sites are shown in Table 5.

Karama and Palm Creek were by far the most productive trap sites, and both recorded relatively similar numbers of mosquitoes, with 49,823 and 45,592 adult female mosquitoes respectively (Table 4). The next most productive of the 11 continuous trap sites were Leanyer Dump (23,971), Leanyer Gate (21,753) and Casuarina (19,617) (Table 4).

When comparing all of the 22 Darwin trap sites, Holmes Jungle had the highest average number of mosquitoes per trap night at 1066 adult females (Table 5). Karama (958), Palm Creek (877), Leanyer Dump (470), Leanyer Gate (418) and Casuarina (377) were the next most productive trap sites out of the 22 Darwin Trap Sites (Table 5).

The average number of Aedes vigilax per trap night for the 11 continuous traps increased from 66.65 in 2009/10 to 154.64 in 2010/11 (Table 6). The increase in average Ae. vigilax numbers was due to higher abundance from July to November inclusive (Fig. 17). The increase in abundance was due to higher than average August, September and October rainfall, which followed on from the higher than usual August high tide, and September and October monthly high tides. This allowed populations to increase dramatically in the coastal swamps around Darwin. The July and August peaks set the scene for the seasonal peak in September, October and November. The 2010/11 Ae. vigilax population was the biggest since monitoring began in 1983/84, slightly bigger than the 1993/94 season (Fig. 13).

Average Culex annulirostris numbers per trap night in the eleven continuous traps decreased from 92.16 in 2009/10 to 67.06 on 2010/11 (Table 6, Fig. 13). The record rainfall in 2010/11 resulted in the main breeding site, the Holmes Jungle reed swamp, being flooded with deep water throughout the mid wet season to early dry season,

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enabling enhanced fish predation on Cx. annulirostris to begin relatively early and then continue to well into the dry season.

Anopheles bancroftii average numbers increased from an average of 10.46 in 2009/10 to 25.05 in 2010/11, while An. farauti s.l. numbers also increased from an average of 4.54 in 2009/10 to an average of 12.59 in 2010/11 (Table 6). Coquillettidia xanthogaster also increased from an average of 17.45 per trap night in 2009/10 to an average of 37.12 in 2010/11(Table 6). This was despite a decrease in optimum breeding sites in the favoured Holmes Jungle reed swamp, indicating other potential breeding sites such as the floodplains of the Leanyer Bomb Range may have been more productive due to the longer and more extensive flooding of the plains.

4.1.1.3 Seasonal occurrence The salt marsh mosquito Ae. vigilax is most common in the Darwin area from September to January inclusive (Fig. 17). Minor numbers can also be encountered in April-August in some years (Fig. 17). In 2010/11, Ae. vigilax was abundant during the months of July to November inclusive (Fig. 17). Abundance of Ae. vigilax is associated with monthly high tides (7.4 m ACD or over) and/or appreciable rainfall events (25 mm and above) during peak abundance months.

The common banded mosquito Cx. annulirostris is most common during the months of January to August. In most years, two peaks in abundance generally occur during these months; an early to mid wet season major peak in January or February, and an extended minor peak during the months of April to June. The early wet season peak is generally a result of initial widespread flooding of the Holmes Jungle and Leanyer swamps, and other swamps and smaller ground depressions in other locations, with high mosquito productivity due to the lack of mosquito larvae predators after initial flooding. The peak in April to June is a result of the larger breeding sites, such as the Holmes Jungle Reed swamp and the Leanyer floodplain beginning to dry out, resulting in the formation of thickly vegetated pools with restricted access for mosquito larvae predators.

In 2010/11, there were two small Cx. annulirostris peaks, in February and May, with the May peak slightly higher than the February peak (Fig. 16). Usually the early to mid wet season peak is impractical to effectively control due to concurrent flooding of over 1000 hectares of the Leanyer and Holmes Jungle swamps and the extensive floodplains near the former Leanyer Bomb Range after the first monsoon rains, although the main concentration of larvae are targeted by aerial control. The early dry season peak is usually associated with shallow flooding in the Holmes Jungle reed swamp, and is thus smaller and easier to control when control of their breeding sites is warranted.

Other important mosquito species such as Cq. xanthogaster, An. bancroftii, An. farauti s.l. and Mansonia uniformis are most abundant in the late wet season and early dry season, when semi-aquatic vegetation growth is abundant and deep flooded areas begin to dry, leaving shallow or relatively isolated pools.

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4.1.1.4 Trapping sites When comparing total numbers of all mosquito species from all monitoring sites, the Karama, Palm Creek and Holmes Jungle sites recorded the highest numbers (Table 5). The high numbers of all mosquito species at these sites was due to very large areas of reed swamp and other wetland breeding areas in the nearby Holmes Jungle reed swamp and upper mangrove areas close to the trap sites. These breeding sites are considerably influenced by rainfall and tides, providing suitable habitats for both freshwater and brackish water mosquito species. This swamp is not targeted by engineering control methods due to the ecological sensitivity and the importance as a fish breeding site. ME does not routinely control mosquitoes other than the salt marsh mosquito in these swamps, unless there is a relatively high risk of mosquito borne disease from Cx. annulirostris or if numbers of this species and other pest mosquitoes such as An. bancroftii become markedly high.

The minimum urban distance buffer of 1.6 km from the edge of these swamps usually results in few problems in the nearby residential areas, apart from those caused by the long dispersing mosquito Ae. vigilax. These trap sites are also influenced to some extent by Ae. vigilax dispersal from further coastal swamps associated with King Creek and the Howard River.

As usual, the northern suburb traps of Karama, Palm Creek, Leanyer Gate, Leanyer Dump, Longwood and Casuarina were the most productive traps, due to the location of the traps between extensive swamp breeding sites and the urban edge of the suburbs (Table 5). Karama was the most productive trap site for Ae. vigilax, recording more than twice as many as the other trap sites in the Darwin Northern Suburbs. Holmes Jungle was the next most productive trap site for Ae. vigilax, followed by Palm Creek, Longwood Ave, Leanyer Gate and Leanyer Dump, which all recorded very similar numbers, followed by Casuarina (Table 5) which still indicates an appreciable pest problem.

Culex annulirostris was most abundant in the traps bordering the Leanyer and Holmes Jungle swamp, followed by the traps near Casuarina Coastal Reserve and Marrara Swamp, with the traps at East Point near the aero club and Ludmilla near Richardson Park (Table 5) indicated less numbers but still at levels for concern posing pest problems and potential disease transmission problems. The Richardson Park results highlight the major storm water drainage issues in the nearby mangrove area of the upper reaches of Ludmilla Creek, while the East Point results indicate grassy ground pools in the area are still productive localised sources.

Other important mosquitoes such as the Anopheles mosquitoes were most abundant at Palm Creek and Karama, while Cq. Xanthogaster, which can be an appreciable pest, was most abundant at Palm Creek and Holmes Jungle (Table 5).

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4.1.2 Vectors & Disease case data 4.1.2.1 Ross River virus and Barmah Forest virus disease

In 2010/11 there were 262 laboratory notified cases of RRV in the Northern Territory (Table 7). The majority of cases were from the Darwin region (190). This was a reduction in RRV cases from 2009/10, when 320 RRV cases were reported in the NT and 234 from the Darwin region and is now the lowest number since the peak in 2008/09 (Table 9).

The number of laboratory reported cases of BFV disease in the NT was 62 in 2010/11, compared to 93 in 2009/10, and this year is also the lowest since the peak in 2008/09 (Table 10). The Darwin region recorded the majority of cases (45), but at the same time recorded a notable decrease (1/3rd) in cases.

The two main vectors of RRV and BFV in the Darwin region of the NT are the northern salt marsh mosquito Ae. vigilax and the common banded mosquito Cx. annulirostris and the peaks in both diseases usually relate to the peak occurrence or longevity of either of the vectors.

Aedes vigilax numbers in Darwin increase from the late dry season, when the tides become large enough to flood breeding areas, and into the early wet season when rainfall floods breeding areas (Fig. 18). Culex annulirostris numbers are relatively high in the early to mid wet seasons and the early dry season (Fig. 18).

The mid to latter part of the dry season results in a relatively low longevity of Ae. vigilax and hence a reduced capacity for it to transmit RRV in this period. This is why large numbers of Ae. vigilax in October - November generally do not correlate with the highest number of RRV cases. As soon as the heavy rain occurs (usually in December or January), the increased day time humidity in areas both near the breeding sites and near people, together with vegetation growth, appears to increase the longevity of Ae. vigilax enough to result in an increase in RRV transmission. This seasonal transition will also involve favourable conditions for the production and exposure of new non immune offspring of wallabies, which is probably the major vertebrate host in the Top End.

In addition, maximum tide levels per month generally increase from mid July to December, thus increasing inundation of the salt marsh habitat. Consequently, Ae. vigilax numbers increase steadily to reach a peak in November to January. The high numbers in November to January are usually a result of highest tides and/or first flooding rains. High tides after January flooding rains and increased rainfall from February to April do not usually result in Ae. vigilax breeding due to the seasonal flooding of all the major breeding habitats, making the habitat unsuited for egg laying and larval production. There are almost no Ae. vigilax present from February to June each year. Unlike temperate areas, seasonal temperature variation does not seem to play a part in the production of Ae. vigilax in the Top End. Maximum temperatures in the day does not vary much, and thus the temperature in the water is unlikely to be a factor affecting larval development and hence adult mosquito production.

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With Cx. annulirostris, there are low numbers in the period September to October before the first appreciable rains. It is only after the first heavy rains that the population begins to rise. The population arising from ephemeral habitats (wet season flooded grasslands or swamps in the process of filling) reaches a peak in January to February, while peak numbers from extensive perennial swamps occur as the swamps dry from late March to around May and reeds lodge over, reducing the impact of fish predation. For example, peaks in Cx. annulirostris numbers can occur in April, May or even June, depending on rainfall in the preceding wet season, the length of time of water in the swamp, and proximity to and extent of the nearest perennial swamp. High numbers of Cx. annulirostris in April, May or June are not correlated with high RRV disease cases because the longevity of Cx. annulirostris is reduced in this period of lower humidity.

The decrease in RRV cases in the Darwin region was in contrast to the record Ae. vigilax numbers in the Darwin area, indicating that the early high Ae. vigilax peaks in September to November inclusive did not result in a large rise in RRV cases. The low December and January Ae. vigilax abundance was very important in reducing the peak season RRV risk in 2010/11. The relatively low Cx. annulirostris numbers in the mid wet season would have also played a major part in the reduced cases in the Darwin region in 2010/11. RRV cases in other regions were either the same as the previous financial year, or slightly lower (Table 9).

The contributing factors to fewer reported RRV disease cases could have included increased immunity in the natural vertebrate hosts, such as wallabies, less numbers of wallaby young, or less exposure of the young wallabies to mosquito vectors. Alternatively, less people may have presented themselves for mosquito borne disease testing. However, these reasons are less likely than the numbers and expected longevity of the vectors during seasons of relatively high and extended wet season rains.

Barmah Forest virus disease cases were a third lower than last year (Table 10). The decrease was mainly due to the decrease in cases in the Darwin region, for reasons similar to those for the decrease in RRV cases.

4.1.2.2 Murray Valley encephalitis virus surveillance Sentinel chicken flocks are used as an early warning system to detect the activity of MVEV and KUNV and to indicate potential risk periods for MVEV and KUNV disease. The sentinel chicken data for 2010/11 is summarised in Table 13 and discussed in Section 6.1. No case of MVE or KUN virus disease were reported in the Darwin region in 2010/11 (Table 11).

4.1.3 Routine Ground Larval Mosquito Control Program Darwin 4.1.3.1 Larval survey and control program

Larval mosquito surveys in the Darwin urban and peri-urban areas are carried out in cooperation between the Darwin City Council (DCC), the Parks and Wildlife Service of the NT (PWSNT), and Medical Entomology (ME), as part of the DoH Northern

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Territory Disease Control Program (NTDCP). ME has produced aerial photo vector control maps with 100m grid references of the Darwin area, and has categorised all the potential mosquito breeding sites. Potential breeding sites are generally inspected by the body responsible for the management of the area, after advice on potential hatches of mosquitoes from ME. These maps have been undergoing an upgrade with recent aerial photography using GIS, which is also compatible with Google Earth and allows maps and breeding site localities to be sent electronically to land managers.

DCC is responsible for the inspection and control of all storm water drains and areas of swamp adjacent to suburban areas except those in Leanyer Swamp, Casuarina Beach/Lee Point area and Darwin Botanic Gardens. DCC responsibility includes Frances Bay, Fannie Bay, East Point Reserve, Vestey's Beach, Mindil Beach, Ludmilla swamp, Coconut Grove area, Nightcliff Foreshore andparts of the Rapid Creek area. The PWSNT areas include Casuarina Coastal Reserve, Darwin Botanic Gardens and Charles Darwin National Park.

ME advises the DCC and PWSNT of specific times and areas to inspect for mosquito breeding. This is generally following high tides, critical amounts of rain, or periods during the dry season when low flows occur in drains. ME frequently inspects the various key sites in certain areas first to determine the current potential of the breeding sites, before advising the other bodies on priority areas and timing for control.

The responsible body for the management of each area usually carries out larval control after large rainfall events or high monthly tides, with advice and assistance by ME. Small localized sites discovered during preliminary surveys by ME after isolated or small rainfall events are usually treated by ME, as these events may not warrant large scale surveys or treatment by DCC or PWSNT. ME also conducts trials with residual larvicide products in various sites, to determine the suitability of these products in different habitats, particularly mosquito breeding sites that are difficult to control due to accessibility or are extensive and time consuming to control. These trials allow the improvement in the management of certain mosquito breeding sites.

4.1.3.2 Larval mosquito survey results The major breeding sites in the PWSNT area at the Darwin Botanic Gardens were a tidally influenced Brackish Fern area at the base of Bullocky Point, and numerous ground depressions and drains east of Gilruth Ave, and in the Mindil Beach car park area. Productivity was usually high in most breeding sites.

The major breeding sites in DCC administrated areas were grassy pools at Vesteys Lake, Lake Alexander, the upper tidal reaches of Ludmilla Creek, and interdune areas and upper tidal flats, drains and crab farm ponds at Kulaluk (Coconut Grove). Mosquito breeding was also controlled at East Point, in particular around the DCC mulch piles and areas of shallow grassy ponding throughout the East Point area, as well as in dune depressions north of the model aero club and tidal flats near Lake

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Alexander. Other productive breeding sites included the Mindil Beach area in the markets car park, the concrete drain between the tennis courts and casino lawns, and grassy pools at Little Mindil. Other breeding sites controlled included Nightcliff foreshore rock pools between the jetty and Nightcliff Pool, Fannie Bay near the Ludmilla wastewater treatment plant, Frances Bay storm water drainage lines, and tidal drains off Rapid Creek Road.

The major breeding sites at Casuarina Coastal Reserve were the upper tidal reaches of Sandy Creek, including the Brackish Fern area that receives freshwater from the Rocklands Drive section of Sandy Creek. Other major breeding sites were numerous large and productive interdune depressions scattered along the coast from Dripstone Cliffs to the mouth of Buffalo Creek, with the Lee Point area containing the majority of these interdune breeding sites.

4.1.3.3 Larval ground control The most common larvicide used was Abate 10SG, which is a sand granule formulation of the organophosphate insecticide temephos. The sand granule formulation has proven to be the most practical larvicide to use during ground operations, as it is easily dispersed by hand and acts quickly to kill larvae. It was the most common larvicide formulation used in DCC control areas and Casuarina Coastal Reserve/Lee Point/Charles Darwin National Park, although S-methoprene pellets were also used in all control areas. The bacterial larvacide Bacillus thuringiensis var. israelensis (B.t.i) was the main larvicide used at the Darwin Botanic Gardens.

S-methoprene 30 day residual pellets were used at Casuarina Coastal Reserve, which included the aerial application of 30 day pellets to a large interdune depression adjacent to the lower reaches of Sandy Creek. This depression is inaccessible on the ground in some parts, and thus necessitates the aerial application of pellets. S-methoprene pellets have the advantage of providing continuous control of mosquito larvae for 30 days. S-methoprene 150 day residual briquettes were also utilised in a number of dune and grassy depressions and creek lines at Casuarina Coastal Reserve, from Dripstone Park to the mouth of Buffalo Creek. The use of briquettes greatly reduced survey and control requirements while maintaining very good control of mosquito breeding.

S-methoprene 150 day briquettes and 30 day pellets were also placed in select areas around the Darwin area, mostly in tidally influenced stormwater drains to provide control in the late dry/early wet season, with breeding sites in Ludmilla Creek, Rapid Creek, Coconut Grove and Fannie Bay treated. All breeding sites at Charles Darwin National Park were also controlled with S-methoprene 150 day briquettes. Localised wet season ground pools around Darwin, such as at East Point, Vesteys Lake, Lake Alexander, Mindil Beach, Fannie Bay, Coconut Grove and Nightcliff Foreshore, were also selectively treated with S-methoprene 30 day pellets.

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4.1.4 Aerial Mosquito Control Program The helicopter larval control program in Darwin is aimed primarily at the northern salt marsh mosquito Ae. vigilax, and the common banded mosquito Cx. annulirostris. Salt marsh swamps within a 5km range of the northern suburbs of Darwin are routinely surveyed by either helicopter or all terrain quad bikes by ME after high tides or critical amounts of rain. The swamps that are surveyed and controlled by helicopter include Leanyer Swamp, the Leanyer bomb crater area, Holmes Jungle reed and mangrove swamps, Micket Swamp and parts of the Shoal Bay communication base Swamp (Fig. 19). Insecticides are applied by helicopter in liquid formulations, primarily the bacterial insecticide B.t.i. or less commonly liquid S-methoprene.

The area at Leanyer swamp and adjacent swamps treated by helicopter in 2010/11 (2119 ha) was higher compared to the previous year (1080 ha). This was due to more control operations required for Ae. vigilax between July and September 2010.

4.1.5 Mosquito Engineering Control Program The Darwin Mosquito Engineering Control Program is a cooperative effort between ME and DCC to maintain and upgrade those Darwin drains which are actual or potential mosquito breeding sites, as well as to rectify depressions that are mosquito breeding sites. It is funded on a 1:2 dollar basis between DCC : DoH in a $332,225 program for 2010/11. It is a major program for ME, involving inspections and maintenance work on existing drains and concrete upgrading of sections of drains where there are demonstrated mosquito breeding problems.

Much of the engineering work in 2010/11 involved desilting the many kilometres of open unlined drains that occur in Leanyer swamp and along the urban outskirts between certain Darwin suburbs and the mangrove boundary. Desilting is required to minimise isolated tide and rain ponding within the drains, which has the potential to allow appreciable mosquito breeding. The main works in Leanyer Swamp involved desilting the main Karama drain (Calytrix Rd drain) and some of the associated lateral drains feeding into the Karama drain, as well as the Leanyer 5 acre block drains that discharge to the swamp (Saddle Court, Impounded-main drain). Major filling operations continued at Vesteys Lake, with a very large breeding site adjacent to East Point Road being filled. Minor filling operations were also conducted around the monsoon forest fringe at East Point Reserve, while desilting of existing drainage lines and construction of new shallow surface drains occurred at Kulaluk in the dune areas opposite Totem Rd. Medical Entomology also contributed appreciable funds to Parks and Wildlife, to fund the desilting of the Sandy Creek low flow pipe outfall channel, as well as approximately 200m of the pipe itself in the tidal flat area. There are still major issues with silt in the pipe from the Sandy Creek weir to the first mudflat.

The extent of concrete upgrades for drains has been limited in recent years, due to the very high cost of concreting limiting the scope of the concrete upgrade portion of the budget. A major upgrade occurred to the Turf Club drain from Playford St to Dick Ward Dve, with a concrete invert and associated erosion prevention walls provided in the open drain.

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Other works occurred outside of the mosquito engineering budget, but in part due to requests/input from Medical Entomology. These included Power and Water upgrading the sludge storage facility at Leanyer Sewage Ponds, to minimise high nutrient ponding and runoff. New all weather sludge storage beds have been constructed, with drainage pipes connecting the runoff to the adjacent sewage pond. Also, filling works are progressing in the disturbed areas to the north of the sewage ponds. These works will benefit adjacent residential areas by reducing the potential for mosquito breeding.

The key to the successful mosquito engineering control program is the continued cooperation between ME and DCC, as well as assistance from the Power and Water Corporation and DLP. The ME database is a valuable tool in identifying mosquito breeding sites. The development of the ME geographic information system will aid in the planning and monitoring of future work programs.

4.1.6 Suggestions for improved vector surveillance and control Mosquito engineering control measures are still required at Lake Alexander, Vesteys Lake, East Point, Mindil Beach, Ludmilla Creek, Darwin Botanic Gardens, Casuarina Coastal Reserve (including Lee Point and Buffalo Creek) and Leanyer swamp. These areas contain very productive salt marsh mosquito breeding sites, most of which can be engineered to prevent or significantly reduce mosquito breeding. This will require the relevant authorities to acknowledge that the local mosquito breeding sites pose a considerable pest and public health problem for people in the nearby suburbs, and that the rectification of these by relevant landowners should be given a high priority. The combined DCC:ME engineering program does not have adequate funds to rectify all of these sites, even in the longer term, and some sites are more correctly the responsibility of various landowners.

Lake Alexander requires minor fill operations in numerous grassy depressions, while Vesteys Lake requires extensive fill operations or minor surface drainage in several large low lying areas to enable surface water runoff. It needs to be recognised that mosquito engineering rectification in these parks should be a high priority, as visitors and adjacent residents are seasonally exposed to mosquitoes and associated RRV and BF disease risk.

Leanyer swamp requires maintenance of the numerous existing open earth drains established under this program. These drains are becoming blocked by mangroves, in particular the main swamp drain from Patterson St. to the site north of the Leanyer Sewage Ponds. Works are also required to minimise water ponding after high tides and rainfall events in the areas of the swamp close to Leanyer and Karama suburbs.

The upper tidal reaches of Ludmilla Creek opposite Richardson Park and Ludmilla School contains an extensive Ae. vigilax and Cx. sitiens breeding site and this site is becoming progressively more extensive and productive each year, with Cx. annulirostris breeding in this site now posing a dry season pest problem. Ponding problems in this area are a result of a silted channel from the Bagot Rd subsoil

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drainage system outfall at the rear of the school to the sewage embankment nearer to Dick Ward Drive. As well as a mosquito problem, the silted drainage channel is also causing a wet season flooding in the Narrows section of Bagot Rd. The outlet channel requires desilting from the Ludmilla School outfall area to the sewage pipe embankment just upstream of Dick Ward Drive. The sewage pipe and embankment needs re-construction to lower the artificial damming and enable a lower R. L. outfall through the embankment. Desilting and vegetation removal of the main channel will also need to be placed on a regular maintenance program by the relevant authority.

The smaller drainage channels in the upper tidal reaches of Ludmilla Creek also require desilting once the outlet channel has been rectified. A report, ‘Lot 5646 Town of Darwin mosquito breeding in the upper tidal reaches of Ludmilla Creek’ was prepared by ME in 2009 for the Department of Planning and Infrastructure in regards to this breeding site but this problem remains to be rectified.

The Darwin Botanic Gardens require extensive mosquito breeding site rectification works, which includes extensive fill operations in low lying areas. Open concrete invert drains and filling could improve drainage of many areas but may not be an aesthetically acceptable option. PWSNT have acknowledged that many sites require rectification, and have earmarked several major breeding areas to be rectified during future major upgrades to the Gardens.

Casuarina Coastal Reserve requires large scale rectification works to rectify numerous interdune depressions that have become mosquito breeding sites, particularly around the Lee Point area. The sand accumulating process from long shore drift just east of Lee Point is gradually creating new interdune mosquito breeding sites, which are more extensive and productive each year. This site requires the importation of sand from the lower beach line, and filling and grading rectification works. If carried out correctly, this would permanently rectify some of the most productive breeding sites in this area similar to what has previously been achieved by ME and DCC in interdune areas in Coconut Grove (Kulaluk area) and other areas in the Casuarina Coastal Reserve.

The largest and most productive mosquito breeding site in Casuarina Coastal Reserve, the Lee Point Pillbox depression (approximately 500m west of Lee Point) requires an engineering solution by sand filling and grading, to prevent appreciable water ponding and mosquito breeding.

The other major mosquito breeding site is the upper reaches of Sandy Creek near the hospital residential houses. PWSNT need to conduct maintenance works on the upper Sandy Creek low flow pipe system, which has a section of damaged pipe that requires replacing. Shallow drainage lines across a former mudflat have been colonised by mangroves because of the failure of the low flow pipe to take all dry flows in the creek direct to the lower mangrove area. The drainage line on this flat now needs clearing and re-grading, as the mangroves have restricted tidal drainage and resulted in an appreciable mosquito breeding site.

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Appreciable mosquito engineering works are also required in the Buffalo Creek boat ramp area, to rectify drainage problems caused by the previous construction of the road to the boat ramp. PWSNT have earmarked several poorly draining areas to be rectified during future extensions to the car park.

In Palmerston, preliminary investigations by ME have revealed that most Ae. vigilax breeding sites occur in the upper tidal reaches of Mitchell Creek, including disturbed tidal areas and a tidally affected sediment basin, and at stormwater discharge points at the mangrove fringe on the west side of Palmerston. Recent ME baseline surveys for the Palmerston Eastern Suburbs have located many appreciable Ae. vigilax breeding sites associated with the upper tidal areas of Mitchell and Brooking Creek, which require rectification where possible, routine control with larvicides, or a combination of both.

Adult mosquito monitoring has indicated there are Cx. annulirostris breeding sites affecting the Palmerston suburbs of Darla and Fairway Waters. The breeding sites of these adult mosquitoes require locating for future rectification. Some of these breeding sites are possibly associated with sediment basins and wetlands, as well as inappropriate stormwater drains.

The trapping at East Arm Boat Ramp indicated there are very productive breeding sites that require rectification. Major breeding sites are constructed sediment ponds and depressions in undeveloped land, as well as poorly draining roadside drainage. The high mosquito breeding represents a potential pest and disease issue to workers and residents within 2 km of breeding sites. The high receptacle mosquito breeding indicated by the trapping in this area also requires locating and rectification to minimise the potential risk of exotic dengue mosquito establishment in the local receptacles.

High numbers of mosquitoes breeding close to the East Arm port areas also pose a risk of local mosquito species entering a vessel and being exported overseas, as well as providing ample breeding sites for exotic mosquito coming in through the port (Tables 36 & 37). These sites will be rectified by further development of the East Arm port, but they need temporary rectification as soon as possible by additional filling and grading, or weekly larval monitoring and larval control by the East Arm port authorities. Medical Entomology has met with representatives from the relevant departments to discuss the required rectification works.

4.2 Ranger Mine

4.2.1 Monitoring program Trapping at Ranger Mine only occurred twice in 2010/11, due to issues with staff turnover at the mine, reduction in operations and issues with their courier service. Ranger Mine environmental staff have indicated the program should be up and running again in 2011/12.

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4.3 McArthur River Mine Routine adult mosquito monitoring commenced at McArthur River Mine in September 2009, at the request of the Environmental Officer at the mine site. Six trap sites were established, four at the mine site, and two at Bing Bong Port. Trapping during the dry season (May to October) was conducted monthly, while fortnightly trapping was conducted over the wet season. Trap results have been discussed in detail in the McArthur River Mine annual mosquito monitoring report for the trapping program.

In summary, the floodwater mosquito Ae. normanensis occurred in seasonally low to high numbers at the mine site from January to April, and was the most common mosquito collected at the mine. Anopheles mosquitoes and Culex annulirostris were generally recorded in low numbers throughout the wet season as well as the dry season, although reached moderate peaks during the late wet season after above average rainfall. The northern salt marsh mosquito Aedes vigilax was recorded in moderate to relatively high numbers at the mine in 2009/10 during December to February, but only in low numbers during December to February in 2010/11, possibly due to the timing of trapping missing peak abundance, or less than favourable dispersal conditions in 2010/11. All other mosquitoes were present in minor numbers at the mine site.

At Bing Bong, moderate to extremely high numbers of Ae. vigilax occurred from December to April in 2010/11, moderate to very high Cx. annulirostris numbers occurred from February to April, while Cx. sitiens was recorded in low to moderate numbers from January to May. Anopheles mosquitoes also reached a relatively high peak in the late wet season at Bing Bong, but were recorded in low to moderate numbers, mainly during the late wet season and early dry season.

A field visit by ME was conducted on the 9th of March 2011 at McArthur River Mine. The primary focus of the field visit was to inspect artificial receptacles for exotic dengue vector mosquitoes. Receptacle mosquito breeding was found mainly in used tyres, with larvae also located in drums/buckets. No exotic dengue vectors were located. Localised ground pools around the mine site were also inspected, with Anopheles mosquitoes and Culex annulirostris found breeding in low levels in depressions at the airstrip, in a cut off drainage area at the run off Mine pad, and in the sewage plant overflow drain and adjacent shallow ground pools.

The complete results and discussion can be found in the report ‘Mosquito Monitoring McArthur River Mine 2010/11’.

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4.4 Groote Eylandt

4.4.1 Mosquito species recorded in Groote Eylandt In 2010/11, 25 mosquito species were recorded on Groote Eylandt (Table 20).

4.4.2 Adult Mosquito Monitoring Program 4.4.2.1 Monitoring program

The three routine adult mosquito monitoring sites on Groote Eylandt are located at the mine site near Angurugu, the wharf area in Alyangula Township and the Golf Club (Figs 4 and 5). An Environmental Adviser from GEMCO conducts trapping on a fortnightly basis. The adult mosquitoes are sent to ME for identification, and comments and results are then forwarded to the Environmental Advisor on Groote Eylandt who coordinates mosquito control as required.

4.4.2.2 Adult Mosquito Numbers The average number of adult mosquitoes caught per trap night in the three routine traps in Alyangula in 2010/11 (11.46) was slightly lower than in 2009/10 (19.18) (Table 21). The prevalent species caught were Culex quinquefasciatus, comprising 19.27% of the total mosquitoes trapped, followed by Aedes vigilax 10.73%, and Ae. notoscriptus 5.45% (Table 21).

The average number of Cx. annulirostris recorded in 2010/11 per trap night (0.15) was lower compared to 2009/10 (2.59) (Table 22).

Average numbers of Ae. vigilax detected per trap night in 2010/11 (1.23) was considerably lower than in 2009/10 (4.41) (Table 22).

Average numbers of Ae. notoscriptus collected during 2010/11 remained at a low level (0.63). Species abundance decreased to a record low (0.37) in 2007/08 during the Ae. aegypti eradication project 2006 (Table 22), and is still in the process of recovering from this substantial reduction in the container breeding mosquito population caused by the insecticide applications during this program.

No Ae. aegypti were detected in Alyangula in 2010/11.

4.4.2.3 Seasonal Occurrence Two of the three adult routine trap sites are located near Alyangula town. The first is at the golf course and the second in the port area, while the third trap site is situated at the mine site, some 20 km south of the township (Figs 4 and 5).

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The rainfall recorded in Alyangula in 2010/11 (1483 mm) was similar to 2009/10 (1591 mm). Appreciable rainfall occurred in between December 2010 and April 2011 (Bureau of Meteorology).

The major breeding sites of Ae. vigilax near Alyangula are the coastal areas near the golf club, the small tidal creeks south of the town, the upper reaches of the mangrove creeks east of the road to Deception Bay near the Ngadumiyerrka community (‘Little Paradise’), and on Connexion Island. A large number of rock pools to the north of Alyangula, near the North West Bluff, may also be capable of producing moderate numbers of Ae. vigilax after the first wet season rains. The pools hold water and become saline from wind borne sea spray. It is probable that a considerable proportion of the Ae. vigilax adult population detected at Alyangula originated from the extensive breeding sites on Connexion Island.

Connexion Island is situated approximately 6 km west of Alyangula, which is within the flight range of Ae. vigilax. During the monsoon months of January and February, Groote Eylandt experiences prevailing north-westerly winds. Past records show, that Ae. vigilax numbers in Alyangula usually increase during this period. This indicates that the adult mosquitoes detected in Alyangula are probably dispersing with the aid of the wind from Connexion Island into the township. Connexion Island has a number of large Ae. vigilax breeding sites that have previously been identified by ME and GEMCO. These include some small tidally influenced areas on the southern and eastern shores of the island, and a large salt lake at the northern end of the island. The salt lake is not subject to regular tides, but become extensively flooded after the monsoon rains.

There is minor Cx. annulirostris breeding in ground depressions on the golf course. However, the major Cx. annulirostris breeding sites near Alyangula are located to the north of the town. There are extensive freshwater swamps and sub-coastal areas of grassland behind Deception Bay, directly north of Alyangula that provides suitable breeding sites for this species. However, in 2010/11, extremely low numbers of this species (total of 7) were recorded (Table 21).

The Alyangula township trap site is close to the port, industrial and commercial areas. These areas often have items such as large tyres, drums, bins and plant machinery that can hold water during the wet season. The presence of breeding receptacles for Ae. notoscriptus near the port area indicate that there is a need to periodically conduct larval surveys and clean up operations near the port area at the beginning of the wet season to reduce the risk of an exotic mosquito establishment.

4.4.3 Vector & Disease case data 4.4.3.1 Ross River virus and Barmah Forest virus disease

RRV disease cases occur mostly during or towards the end of the wet season. Ross River and Barmah Forest virus disease cases on Groote Eylandt have been relatively low since 1992/93. One to five cases per year of both diseases seem to reflect the normal status (Fig. 15).

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In 2010/11, there were 12 reported cases of RRV disease in East Arnhem (Table 7), but no cases were recorded on Groote Eylandt. There were also five BFV disease cases recorded in East Arnhem (Table 8), with one reported case from Umbakumba. Aedes vigilax and Cx. annulirostris are the main vectors for these diseases, and these species occurred in very low numbers in the Alyangula town area.

4.4.3.2 Murray Valley encephalitis virus surveillance In cooperation with GEMCO environmental staff, a sentinel chicken flock was established in Alyangula in April 2006. Sentinel chicken flocks are maintained, bled monthly and tested for flavivirus in a combined program between DPIFM, DoH, and the volunteer sentinel chicken carers. In Alyangula, the flock is located in a residential area in the eastern part of the town (Fig. 4).

In 2010/11 sentinel chickens in Alyangula were bled 11 times, with no seroconversions to MVE or KUN (Table 13). This indicated that the ecology on Groote Eylandt is not optimal for MVE or KUN virus, and may be due to the lack of large populations or breeding sites for the water bird hosts that include herons and egrets, and the relatively low population of Cx. annulirostris.

4.4.4 Suggestions for improved vector surveillance and control It is important to regularly maintain all storm water drains in urban areas to

discourage mosquito breeding. Drains that are not regularly cleared of vegetation, and do not have the drain floor graded to eliminate depressions, can pool water from wet season rainfall or dry season low flow. Pools that form along drain lines that have dry season low flows often have a high organic content from vegetation and debris that collects in the drain. These pools are often associated with the presence of Cx. quinquefasciatus and Cx. annulirostris larvae. The adults of these species have been detected in relatively high numbers at the mine and the golf course site on Groote Eylandt. It is recommended that a storm water drain maintenance program be implemented in Alyangula and the mine site, and that any drains that require maintenance are cleared and graded before each wet season.

In light of the importation and establishment of Ae. aegypti in 2006, prior to its

elimination in 2008, it is recommended that exotic Aedes receptacle breeding surveys be conducted by ME routinely in Alyangula. In addition, receptacle surveys should be conducted on a periodic (1-3 years) basis in Umbakumba and Milyakburra and other small outstations in the area that are considered to be at risk to an exotic vector incursion through overseas importations (IFFV landings). The surveys should include premise-by-premise surveys for receptacle breeding mosquitoes in residential areas, as well as person landing and adult trapping targeting exotic vector species. The surveys should be undertaken in liaison with AQIS officers, indigenous ranger groups and GEMCO Environmental staff.

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4.5 Nhulunbuy

4.5.1 Mosquito species recorded in Nhulunbuy Thirty five mosquito species were collected from the Gove Peninsula in 2010/11 (Table 16). The most important mosquito species in terms of pest and diseases are shown in Table 17.

4.5.2 Adult Mosquito Monitoring and Control Program 4.5.2.1 Monitoring program

There are six routine adult mosquito monitoring sites in Nhulunbuy (Fig. 6). Traps are currently located at Wallaby Beach, Buffalo Creek, Rear Jasper, Contractors Village, the Industrial Estate and Nhulunbuy South. There are five traps that have been in continuous operation since 1990/91and six since the Industrial Estate trap was started in 2004/05. DoH Environmental Health Officers set and collect the traps on a fortnightly basis. Once collected, the mosquitoes are sent to ME for identification, and the results, comments and control advice are forwarded to the Nhulunbuy Corporation Limited (NCL), Nhulunbuy Environmental Health Officers, Centre for Disease Control Nhulunbuy and Arnhem Land Pest Control (ALPC). The NCL then organises mosquito control as required.

4.5.2.2 Adult Mosquito Control ‘Fogging’ or adulticiding by Ultra Low Volume applications (ULV) conducted by Arnhem Land Pest Control under direction from NCL is based on adult mosquito monitoring results, with public complaints also influencing fogging frequencies. Fogging thresholds have been previously set for the mosquito species Ae. vigilax and Cx. annulirostris (Montgomery & Love 1995). Fogging is recommended once a week for two weeks, or until numbers go below the thresholds of Ae. vigilax when numbers exceed 50/trap night and Cx. annulirostris when numbers exceed 100/trap night at any of the relevant trap locations. The fogging frequency can increase to three times a week for two weeks on occasions when there are over 100/trap night for Ae. vigilax and over 200/trap night for Cx. annulirostris.

4.5.2.3 Adult mosquito numbers The average number of all mosquitoes caught per trap night in the five continuous monitoring traps in 2010/11 (412.43) was the highest recorded since 1994/95 (Table 18). This was mostly due to very high Ae. vigilax numbers recorded between October and December 2010.

Culex annulirostris (99.05 average/trap night) and Ae. vigilax (121.25 average/trap night) were still the two most commonly detected species in Nhulunbuy in 2010/11 (Table 17).

The routine trap sites that usually record high numbers of Ae. vigilax in Nhulunbuy are Buffalo Creek, Wallaby Beach, Contractors Village and Nhulunbuy South. These sites are in close proximity to six of the major salt marsh mosquito breeding areas on

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the Gove Peninsula; the upper tidal areas of No Name Creek, the Special Purpose Lease area 270 at the reclaimed red mud ponds (SPL270), Crocodile Creek, the western mudflats, Buffalo Creek and Rainbow Beach.

Historically, there have been large-scale emergences of Ae. vigilax detected on the Gove Peninsula following the first monsoonal rains. The highest Ae. vigilax total numbers in 2010/11 were detected at the Wallaby Beach (4405), Buffalo Creek (2339) and Nhulunbuy South (3030) trap sites (Table 17).

The major breeding sites for Cx. annulirostris on the Gove Peninsula are in the depressions on the SPL2