This article summarises the 2013-14 wet season in Darwin urban in relation to rainfall, mosquito numbers and notified Ross River virus cases.

Adult mosquito traps are commonly used in biosecurity surveillance for the detection of exotic mosquito incursions or for the demonstration of elimination. However, traps are typically deployed without knowledge of how many are required for detecting differing numbers of the target species. The aim of this study was to determine the sensitivity (i.e., detection probability) provided by carbon dioxide-baited EVS traps for adult female Australian southern saltmarsh mosquitoes, Aedes camptorhynchus, a recent biosecurity problem for New Zealand. A mark-release-recapture study of three concurrently released cohorts (sized 56, 296, and 960), recaptured over four days with a matrix of 20 traps, was conducted in Australia. The detection probability for different numbers of traps and cohorts of different sizes was determined by random sampling of recapture data. Detection probability ranged from approximately 0.3 for a single trap detecting a cohort of 56 mosquitoes to 1.0 (certainty of detection) when seven or more traps were used. For detection of adult Ae. camptorhynchus around a known source, a matrix of traps provides a strong probability of detection. Conversely, the use of single traps deployed over very large areas to detect mosquitoes of unknown entry pathway is unlikely to be successful. These findings have implications for the design of mosquito surveillance for biosecurity.

A program to eliminate the exotic mosquito capable of transmitting the dengue virus, Aedes aegypti, has been under way in Tennant Creek since 22 February 2004. This followed the finding of this mosquito via routine adult mosquito trapping on 17 February 2004. Further surveys by the Medical Entomology Branch (MEB) of the Centre for Disease Control (CDC) of the Northern Territory Department of Health and Community Services (DHCS) have indicated to date that the dengue mosquito is firmly established in Tennant Creek. Elimination of this mosquito will take a major effort by health and local authorities as well as by the general public in Tennant Creek.

In Alice Springs, the Ilparpa Swamp is the most productive mosquito breeding site for the common banded mosquito, Culex annulirostris. The swamp is of major public health concern due to potential outbreaks of Murray Valley encephalitis (MVE), with the virus transmitted by this mosquito. In 2001, extensive flooding and two MVEV disease cases led to the first aerial control of Ilparpa Swamp, with aerial control also carried out in 2010. In January 2015, Alice Springs again received heavy rainfall associated with monsoonal activity in the north-east, indicating a possible MVEV disease risk. DoH responded by carrying out another aerial control operation in Ilparpa Swamp, with the successful operation jointly funded by the Power and Water Corporation and the Department of Lands & Planning.

The introduction of target-specific adult mosquito traps (Biogents® (BG) sentinel mosquito traps) in 2009/10 to detect exotic dengue vectors at Darwin port facilities has apparently increased the ability and frequency of their detection. The latest detection of Aedes aegypti at Frances Bay in Darwin in January 2011 was followed by subsequent successful elimination measures and heightened surveillance responses, which indicated no further presence of adults or larvae of this species.

Darwin, in the tropical north of Australia, is subject to high numbers of mosquitoes and several mosquito-borne diseases. Many of Darwin’s residential areas were built in close proximity to tidally influenced swamps, where long-term storm-water run-off from nearby residences into these swamps has led to anthropogenic induced ecological change. When natural wet-dry cycles were disrupted, bare mud-flats and mangroves were transformed into perennial fresh to brackish-water reed swamps. Reed swamps provided year-round breeding habitat for many mosquito species, such that mosquito abundance was less predictable and seasonally dependent, but constant and often occurring in plague proportions. Drainage channels were constructed throughout the wetlands to reduce pooled water during dry-season months. This study assesses the impact of drainage interventions on vegetation and mosquito ecology in three salt-marshes in the Darwin area. Findings revealed a universal decline in dry-season mosquito abundance in each wetland system. However, some mosquito species increased in abundance during wet-season months. Due to the high expense and potentially detrimental environmental impacts of ecosystem and non-target species disturbance, large-scale modifications such as these, are sparingly undertaken. However, our results indicate that some large scale environmental modification can assist the process of wetland restoration, as appears to be the case for these salt marsh systems. Drainage in all three systems has been restored to closer to their original salt-marsh ecosystems, while reducing mosquito abundances, thereby potentially lowering the risk of vector-borne disease transmission and mosquito pest biting problems.

Ross River virus (RRV) causes the most common human arbovirus disease in Australia. Although the disease is nonfatal, the associated arthritis and postinfection fatigue can be debilitating for many months, impacting on workforce participation. We sought to create an early-warning system to notify of approaching RRV disease outbreak conditions for major townships in the Northern Territory. By applying a logistic regression model to meteorologic factors, including rainfall, a post-estimation analysis of sensitivity and specificity can create rainfall cut-points. These rainfall cut-points indicate the rainfall level above which previous epidemic conditions have occurred. Furthermore, rainfall cut-points indirectly adjust for vertebrate host data from the agile wallaby (Macropus agilis) as the life cycle of the agile wallaby is intricately meshed with the wet season. Once generated, cut-points can thus be used prospectively to allow timely implementation of larval survey and control measures and public health warnings to preemptively reduce RRV disease incidence. Cut-points are location specific and have the capacity to replace previously used models, which require data management and input, and rarely provide timely notification for vector control requirements and public health warnings. These methods can be adapted for use elsewhere.

There has been some public concern over a possible increase in blowfly numbers since the introduction of Wheelie bins. Some opinion attributes this possible increase in blowfly numbers to the reduction in bin collection frequency from twice per week to once per week. To aid in resolving the issue the Medical Entomology Branch of the NT Department of Health and Community Services, set up an experiment to determine what link existed between Wheelie bins and blowfly numbers.

Australian encephalitis (AE) is an arboviral (ie arthropod borne or in this case more specifically mosquito borne) disease caused predominantly by Murray Valley encephalitis virus, and occasionally by Kunjin virus. The disease was initially recognised as occurring in epidemics chiefly centred about the Murray-Darling system, but now is known to occur Australia-wide. The last major epidemic was in 1974; 58 people were affected, including five from the Northern Territory (NT).

Sentinel chicken flocks are used to monitor flavivirus activity in Australia. The main viruses of concern are Murray Valley encephalitis (MVE) and Kunjin which cause the potentially fatal disease encephalitis, in humans. Currently 30 flocks are maintained in the north of Western Australia, 9 in the Northern Territory, 12 in New South Wales and 10 in Victoria. The flocks in Western Australia and the Northern Territory are tested year round but those in New South Wales and Victoria are tested only from November to March, during the main risk season. Results are coordinated by the Arbovirus Laboratory in Perth and reported bimonthly.

The Northern Territory Government proposes to convert Berrimah Farm on the southern outskirts of Darwin, NT into an urban residential subdivision. Areas of Berrimah Farm are located within 1.5km of tidal mangrove areas, and were expected to experience seasonal populations of pest biting midges. Seasonally flooded areas located within and adjacent to Berrimah Farm were also expected to be sources of pest and disease carrying mosquitoes. Due to the potential for significant populations of biting insects, the Department of Planning and Infrastructure (DPI) commissioned Medical Entomology (ME), of the Department of Health and Families (DHF) to conduct a biting insect assessment of the Berrimah Farm site.

The Top End of Australia is home to plenty of creatures such as mosquitoes, biting midges, and a wide range of other insects that can leave locals and visitors alike with some unwelcome pain or discomfort, as well as possibly contracting an insect borne disease. Faced with the daunting array of biting insects, many people often ask, “what is the health risk of this or that insect, what is the best way to protect against the bites and stings, what repellent is the best, or even do sand flies really urinate on your skin?” This introduction to the various culprits and the range of ways to protect yourself will hopefully help make your life in the Top End a bit less painful and safer.

A biting insect assessment was conducted at the Andranangoo Creek West and Lethbridge Bay West mining prospects from the 29th September to the 1st of October 2005. This included detailed ground surveys for actual and potential mosquito breeding sites, assessment of aerial photography for potential mosquito and biting midge breeding sites, and initial adult biting insect trapping at both mining prospects. The early report production meant that information from subsequent peak season adult biting insect trapping in November 2005, and January and May 2006 had to be produced in a separate supplementary report. Therefore some conclusions in the first report were drawn based on field inspections and desktop observations, and not on trap data. The following report highlights the findings of the supplementary trapping, with new conclusions in regards to mosquitoes and biting midges. Trapping conducted for the Andranangoo Creek West and Lethbridge Bay West Biting Insect Assessment Report (Warchot & Whelan 2005) is referred to as ‘initial trapping’ in this supplementary report.

Burnside Operations Pty Ltd plan to commence mining at the North Point and Princess Louise mine sites, located in the East Burnside Project Area approximately 130km south-east of Darwin. The mining method will be open cut, with ore to be transported to Union Reefs Gold Mine for processing. Workers are to be housed at the mine camp at Cosmo Village. Mine sites have the potential to create or exacerbate mosquito breeding, potentially from the creation of water dams, wetland filters, borrow pits, sediment traps, dry season water discharge, waste water disposal, as well as the construction of roads and mine waste dumps. Mine sites also have the potential to introduce new mosquito species into the Northern Territory, such as the dengue mosquito Aedes aegypti from North Queensland, if equipment was to be sourced from this area. As part of the environmental process, all major development in the NT is required to consider mosquitoes during the preparation of Environmental Impact Statements or Public Environmental reports, to ensure new development does not create new mosquito breeding sites, and also to protect the health of workers.

Matilda Minerals Limited (Matilda) proposes to develop sand mining operations at Andranangoo Creek West (Andranangoo) and Lethbridge Bay West (Lethbridge), Melville Island, Tiwi Islands, Northern Territory. The proposed operation will extract high grade heavy minerals (HM), specifically zircon and rutile, for export to China. It is estimated that a total of 99,000 t of zircon and rutile will be exported during the anticipated sand mining operation over three and half years. A proposal to mine both sites was submitted to the NT Government in the form of a Notive of Intent Document (URS, 2005). The NT Government determined the project is to undergo formal environmental assessment in the form of an Environmental Impact Assessment (EIS). Part of the EIS process is to conduct a biting insect assessment of the general project areas to determine any public health risks to workers and the potential for mining activities to alter the natural environment and create further biting insect breeding sites. The Medical Entomology Branch was commissioned by URS Australia on behalf of Matilda Minerals to undertake a biting insect assessment at both proposed sandmining sites.

Darwin Clean Fuels Pty Ltd plan to establish and operate a Condensate Processing Facility in Section 5720 and part Section 5633 at the Darwin Business Park at East Arm. The Condensate Processing Facility will produce a range of products, principally unleaded petrol, diesel and kerosene/jet fuel. It is anticipated that the condensate would be sourced principally from the Bayu Undan field in the Timor Sea and North West Shelf off Western Australia. Surface water ponding and mosquito breeding has been an issue in the East Arm area, primarily due to reclamation works conducted for the development of Darwin Business Park and the port facility. Water ponding and mosquito breeding has also been located in Section 5720 and part Section 5633 by the Medical Entomology Branch during previous surveys. The Darwin Business Park is also located adjacent to extensive mangrove areas of Bleesers Creek, Elizabeth River and Hudson Creek, which are expected to be large sources of pest biting midges. Due to the proposed development site and adjacent areas containing potential mosquito breeding sites, and the close proximity of mangrove areas, which are potentially large sources of pest biting midges, the Medical Entomology Branch (MEB) was commissioned by URS Australia Pty Ltd on behalf of Darwin Clean Fuels Pty Ltd to conduct a Biting Insect Assessment for the proposed facility.

A Hazchem Storage Facility is proposed at Section 4239, Hundred of Bagot. Section 4239, Hundred of Bagot is located at Hidden Valley adjacent to extensive mangrove areas of Bleesers Creek and Reichardt Creek in Frances Bay, Darwin Harbour. Section 4239 is proposed to be subdivided in future, with the proposed Hazchem Storage Facility to be built within a 4ha site in Section 4239. The areas adjacent to the proposed development area were also identified as being subject to seasonal pest problems from the salt marsh mosquito Ochlerotatus vigilax (Whelan et al 1994). Other mosquito species of potential significance in the proposed development area include Culex annulirostris and Coquillettidia xanthogaster (Whelan et al 1994). Ochlerotatus vigilax is a vector of Ross River virus (RRV) disease and Barmah Forest virus (BFV) disease, while Culex annulirostris is a vector of RRV, BFV, Murray Valley encephalitis virus (MVEV) disease and Kunjin virus (KUNV) disease. The numbers of these species of mosquitoes in this area indicated there are seasonal risks for mosquito borne disease transmission in the development area. The Medical Entomology Branch (MEB) has been asked to identify any biting insect pest or potential human health problems in the development area, and provide advice on the magnitude of the problem. To do this MEB has referred to past biting insect investigations in the development area (Whelan et al 194), as well as examined the proposed plans for the potential of the development to create or exacerbate existing biting insect problems.

It is assumed that mosquito breeding areas within proposed residential development will be rectified as a matter of course, as the suburbs are developed. However, there are a number of mosquito breeding sites that are outside the suburban area that will require rectification as soon as possible, before considerable numbers of residents move into the area.

The objectives of the biting insect assessment of the proposed Darwin City Waterfront Redevelopment area is to outline actual and potential biting insect problems within the redevelopment area, and to provide mitigation strategies to prevent or minimise biting insect problems. As with most coastal areas in the NT, the proposed development area is potentially subject to mosquito and biting midge pest problems, and potential mosquito borne disease problems.

The Blacktip Project consists of both offshore and onshore components. The onshore components include the construction and operation of an onshore processing plant, construction and operation of 3km of buried onshore pipeline, and the construction of access roads and construction camp. There were potential biting insect concerns associated with these onshore components of the Blacktip Project. EcOZ Environmental Services was commissioned by Woodside Energy Limited (Woodside) to assist in the preparation of a Draft Environmental Impact Statement (EIS) for the Blacktip Project. EcOZ Environmental Services then commissioned the Medical Entomology Branch of the Department of Health and Community Services to provide information on biting insects likely to affect the Blacktip Project.