MOSQUITOES & BITING MIDGES (SANDFLIES) IN THE TWEED SHIRE Updated 19/12/05

Background

Mosquitoes and biting midges belong to the insect order Diptera which include many common flies such as mosquitoes midges and house flies.

Mosquitoes (Culicidae) and biting midge (Ceratopogonidae), sometimes erroneously called sandflies, are abundant in this region of Australia. The female mosquito and biting midge adults generally require protein in the form of blood meal to effectively develop their eggs and to complete the reproductive process. These insects are opportunistic feeders that will feed on many species of birds and mammals. Humans tend to be the most abundant source of food in many local areas close to wetland breeding areas favoured by these insects.

The extensive areas of wet low-land and intertidal areas along the Tweed coastal districts contain many suitable breeding sites for these insects. As a result of the proximity of these low-lands to urban areas, biting insect nuisance is likely to occur seasonally in many areas.

As a general rule, the areas where biting midge and mosquito problems will regularly be a nuisance to our human populace will be within 1km of extensive biting insect breeding areas. Maps of biting midge and mosquito breeding areas have been produced for most of the Tweed coastal districts. This information can be used to estimate those areas where potential biting insect problems will most likely occur.

Council’s Environment and Community Services Division offers residents, tourist operators and developers advice on mosquito and midge control and avoidance in the Shire. If residents have biting insect problems it is useful to catch some of the offending insects and store them in a jar containing a mix of 50% methylated spirits and water. Council officers can then identify the species which assists in finding the likely breeding areas.

Mosquitoes Affecting Coastal Districts

The major mosquito nuisance in this area is caused by several species of saltmarsh breeding mosquitoes. These mosquitoes breed in salt to slightly brackish water. Following heavy rainfall these mosquitoes may also be found in fresh water ground pools.

The following mosquito species are generally the most abundant species in coastal areas.

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1. Ochlerotatus vigilax

This common saltmarsh mosquito causes more nuisance complaints from Tweed residents than any other mosquito species.

Ochlerotatus vigilax breeds principally in temporary salt to brackish water pools flooded by the highest monthly tides. Eggs of this species are laid around the drying margins of these pools and may lie dormant for many months.

Hatches may be triggered by tides or rainfall. Eggs may hatch in instalments as various environmental conditions in the breeding pools such as temperature, salinity and specific dissolved oxygen levels are met. Breeding areas are found amongst poorly flushed mangroves surrounding Cobaki and Terranora Broadwaters, open tidal saltmarshes and on low lying agricultural pastures that receive occasional tidal flooding along the length of the Tweed River and parts of Cudgen Creek.

Ochlerotatus vigilax is a savage biter by day or night and an effective carrier of Ross River virus. This mosquito disperses widely from its breeding areas and appears to be attracted to the hill and ridge tops overlooking tidal flats. The species may be a problem many kilometres from its breeding source.

Areas badly affected at times are Cobaki Inlet, Piggabeen, Bilambil Heights, Terranora and parts of West Tweed Heads.

This species often reaches plague numbers late summer, particularly when a long dry spell or drought has recently been broken by rainfall. Abnormally high tides caused by storm surges may also cause extensive Ochlerotatus vigilax hatches.

2. Verrallina funerea

This species breeds in shaded fresh to brackish ponds, often amongst emergent reed growth or under the cover of mangrove, casuarina, tea tree or palm thickets.

Like the previous species, it is a savage biter both during the day and at night, often biting in large numbers, though it tends not to travel far from well shaded areas surrounding its breeding sites.

Verrallina funerea is often found breeding in areas slightly more elevated than Ochlerotatus vigilax breeding sites, particularly where springs or creeks feed into brackish water habitats. Eggs are laid around the drying margins of pools and may remain dormant for many months awaiting hatching stimuli.

Extensive breeding sites exist surrounding parts of Cobaki Broadwater, Terranora Broadwater, Fingal, Chinderah, Tumbulgum, Stotts Island and coastal tea tree swamps surrounding Cudgen Lake and Cudgera Creek.

Residential areas in close proximity to these sites are often affected by these mosquitoes following heavy rainfall, particularly if corridors of thick vegetation are continuous between breeding sites and residential areas.

Verrallina funerea is a possible carrier of Ross River virus.

3. Culex sitiens

The third major saltmarsh mosquito pest in the area is Culex sitiens which breeds in fresh to brackish ponds in similar habitat to Ochlerotatus vigilax.

This species usually reaches population peaks during late summer when rainfall has diluted salinity in tidal saltmarsh pools and flooded low-land agricultural flats.

Eggs of this species are deposited in rafts on the surface of the water. Culex sitiens is slower than the two previous aedes species to build up population peaks, due to the fact that the aedes mosquitoes eggs are already awaiting hatching stimuli in their preferred larval habitat prior to the pools flooding.

Breeding areas are well scattered throughout the Tweed coastal area.

Culex sitiens is a night feeder and may disperse widely from its breeding areas. Residential areas around Cobaki Inlet, Terranora and Tumbulgum are often affected by this mosquito.

Culex sitiens is not considered a disease vector in this region.

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Other nuisance species

Following heavy rainfall a number of other mosquito species may become pests. Some of these mosquitoes breed in flooded ground pools, drains and pasture areas. Another group of mosquitoes breed in water filled containers such as buckets, old tyres, poorly aligned roof gutters and pot plant holders.

Mosquito Borne Disease

Viruses such as Ross River virus and Barmah Forest virus, which may cause disease in humans, are spread by several local species of mosquitoes. Dog heartworm is also spread locally by mosquitoes.

Ross River virus is the main mosquito borne virus affecting local residents, however, Bormah Forrest virus infection appears to be increasing.

Ross River virus (RRV) is a mosquito-borne virus found naturally in Australia. In nature the virus is passed between mosquitoes and wildlife. Kangaroos and wallabies in particular are commonly found infected with the virus.

Humans bitten by an infected mosquito may develop a disease called Epidemic Polyarthritis which is commonly known as ‘Ross River virus disease’.

The disease was first recognised in NSW in 1928 and the virus itself isolated from mosquitoes along the Ross River near Townsville in 1963.

Correct diagnosis of the disease can only be positively carried out by a doctor when confirmed by blood test. RRV disease is a notifiable illness with pathology laboratories notifying state health departments of confirmed cases.

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Humans and other animals are infected by RRV after being bitten by a mosquito carrying the virus. Mosquitoes pick the virus up from infected animals. Some species of mosquitoes may short-cut this cycle by passing the virus through their eggs to subsequent mosquito generations. Humans infected by RRV may pass the virus back to mosquitoes if they are bitten during the last few days of the incubation period and for several days following onset of symptoms.

In Tweed coastal districts, the virus is thought to be principally spread by the saltmarsh mosquito Ochlerotatus vigilax. The fresh water ground pool breeding Culex annulirostris is a likely vector in western areas of the Shire. Domestic container breeding Ochlerotatus notoscriptus mosquitoes are also likely carriers.

RRV transmission occurs when temperatures are warm enough for the virus to be active combined with high numbers of mosquito carriers following rainfall or after high spring tides in coastal areas flooding poorly drained saltmarsh. In Tweed Shire the disease is usually most active between December and April.

Research in the Brisbane area during an outbreak of RRV disease in 1994/95, indicated several domestic breeding mosquito species which breed in water holding containers such as bird baths, old tyres and blocked roof gutters were also likely RRV vectors in this region.

The incubation period of RRV infection varies from three days to three weeks, but symptoms usually appear within seven to fourteen days of being bitten.

People infected by RRV may develop a wide range of symptoms. Adults appear to be affected more so than children. Many people infected with RRV will not develop any noticeable symptoms, those that do may include: painful or swollen joints, sore muscles, skin rash, fever, fatigue, headache, dizziness, swollen lymph nodes, nausea and a general feeling of being unwell.

Fever, nausea and skin rash usually disappear within the first two weeks of illness. Joint and muscle pain, lingering fatigue and depression may last much longer in some individuals.

Many people with RRV disease will still feel unwell at three months and up to a quarter of sufferers will still have some symptoms after a year.

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Treatment Of Ross River Virus Infection

There is no medical cure for RRV infection. Medical treatment is aimed at easing joint pains and swelling and minimising fatigue and lethargy. Aspirin appears useful to many sufferers in reducing pain and inflammation. Rest is very important for RRV disease sufferers, particularly during the early stages of the disease.

Stress, physical fatigue and alcohol may cause symptoms to worsen and prolong the duration of the illness.

The often long duration of this disease can be very taxing on individuals and their families. As this disease afflicts many active people in the work force the costs to individuals and the community due to time lost at work can be high.

Long term sufferers need to be reassured that they will eventually get well again.

How To Avoid Ross River Virus Infection

Avoiding mosquito bites is the obvious way of protecting yourself from RRV infection.

The following suggestions will assist in reducing mosquito nuisance and disease risk:

• Insect screening Effective insect screening should be provided to all windows and doors.

• Mosquito avoidance Avoid outdoor activity at dawn and dusk or other periods when mosquito numbers are high. If activity at this time can not be avoided wear long loose fitting clothes and an effective repellent, usually containing between 5 and 20% n diethyl toluamide (DEET).

Domestic mosquito breeding Eliminate mosquito breeding places on your property by.

• Screening all openings to water tanks and septic tanks. Ensure potential water holding containers such as old tyres, buckets, bottles etc. are not stored outdoors where rainwater may fill them. Place sand in holding trays under pot plants to absorb water. Empty and refill birdbaths and pets drinking dishes at least once weekly. Keep roof gutters clean, blocked or poorly aligned roof gutters may hold water for long periods providing highly productive mosquito breeding sites. Keep ornamental ponds stocked with goldfish or native species that will feed on mosquito larvae, Tweed Council can usually supply native mosquito feeding fish to stock small ponds.
       

• Mosquito harbouring areas Mosquitoes like to harbour in shaded moist places and may aggregate in these areas well away from their breeding sites. By limiting dense vegetation in the yard, mosquitoes will find the area less attractive to harbour in.

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This Council has been actively involved in mosquito abatement since 1983. Tweed Council has a formal agreement with Gold Coast City Council, Logan City Council and Redland Shire Council to cooperate in mosquito research and information exchange aimed at reducing mosquito nuisance and disease risks in South East Queensland and Northern New South Wales.

The following mosquito related activities are carried out by Tweed Council’s Environment and Community Services Division:

• Mosquito monitoring traps Council cooperates with NSW State Health by trapping adult mosquitoes weekly near major mosquito breeding areas at West Tweed Heads and Terranora. These traps emit carbon dioxide to attract the mosquitoes which are then drafted by a small fan into a holding container. Trapping is used to monitor the mosquito species present and seasonal abundance. Around twenty different mosquito species are trapped each year. Trapped mosquitoes are chilled then sent live to Sydney’s Westmead Hospital to be checked for viral incidence, this hopefully gives early warning of potential viral disease presence. Information gathered by this programme over many years helps us understand the factors influencing mosquito abundance and RRV prevalence. The following graph shows the average number of mosquitoes trapped per night during the 2004/2005 season at West Tweed Heads and Terranora compared to long term averages.

• Habitat reduction Council has carried out some innovative forms of habitat modification to reduce the breeding potential of mosquitoes in semi-tidal saltmarshes without the use of chemicals. Modifications such as runnels in saltmarsh, partial tidal impoundments, increased back water flushing, and reducing drain water acidity have reduced mosquito breeding by changing the environment just enough to allow fish and other mosquito predators to more effectively predate on mosquito larvae or ‘wrigglers’. These modifications have also reduced the sites suitability as mosquito egg laying sites. The modifications work at their best when seasonal rain conditions are average to above average. During and following long droughts, small mosquito feeding fish numbers are often too low to effectively reduce mosquito numbers.

• Aerial larviciding When extensive areas hatch mosquito larvae following heavy rain or higher than usual spring tides, an agricultural aircraft fitted with customised application equipment may be deployed to treat these areas. Traditional larvicides such as Abate or more recently developed biological larvicides can be used.

• Biological larvicides Council uses a bacterial larvicide called Bti to spray mosquito breeding areas when warranted. This larvicide is specific to mosquitoes and several other closely related flies. Bti poses no harm to other aquatic non-target organisms. Bti is ingested by feeding mosquito larvae causing death, usually within 24 hours. Another biological chemical which has proven particularly effective in local research trials is the insect growth regulator methoprene. This chemical can be applied to breeding areas in sustained release formulations which inhibit mosquito wrigglers from turning into adult mosquitoes for up to six months in small infrequently flooded pools. Methoprene is also quite specific in its action, posing no risk to fish, crabs, amphibians and water birds.

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Biting Midge (Sandflies) In Tweed Shire

Like mosquitoes, the female biting midge takes a blood meal to provide protein to develop her eggs. The direct impact on human health caused by biting midge is due to allergens in midge saliva reacting on people of varying degrees of sensitivity and immunity. Most people find the bites uncomfortable and distressing with the irritation leading to scratching and sometimes infected sores.

Biting midges are not known to carry any diseases affecting humans in Australia.

There are three major pest species of estuarine breeding biting midge affecting Tweed coastal areas. There is also a forest breeding species which seasonally affects many other areas of the Shire. These species are described below.

1. Culicoides molestus

This species is most commonly found breeding in clean flocculated sand, in the open or under light mangrove cover between mean tide level and mean high water spring tide level. Culicoides molestus has colonised the beaches of artificial canal developments on the Tweed River. They can also be found breeding on most sandy tidal river foreshores and suitable river sandbars.

Larval densities can be extremely high in suitable habitat. The large sandbar off Tony’s Island at Banora Point provides a very suitable habitat with over 30,000 midge larvae per square metre recorded on parts of the bar. It is thought that high trapped nutrient on the bar from roosting birds supports the very high midge productivity on this bar. Culicoides molestus also breeds on the lower reaches of Cudgen Creek, Cudgera Creek and Mooball Creek.

Adult Culicoides molestus midge will travel at least 1km from the larger breeding areas. Residents living on hill tops overlooking these breeding areas are often affected more adversely by these midge than residents at lower elevations close to the breeding sites.

Culicoides molestus bites most actively the week following full and new moon.

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 2. Culicoides subimmaculatus

This species, or more likely a complex of species yet to be determined, breeds in clean to muddy sand in the open or under light mangrove cover between mean high water neap tide level and mean high water spring tide level.

Note: neap - small tidal range about quarter and three quarter moon and spring - large tidal range about new and full moon. 

Culicoides subimmaculatus breeds along much of the Tweed River foreshore, particularly near stormwater outflows and along the fringe of mangrove growth on Tweed River islands. The species is also abundant along the middle reaches of Cudgen, Cudgera and Mooball creeks.

Culicoides subimmaculatus adults are generally only a pest within 500m of their breeding areas. This range may double around extensive breeding areas such as the Ukerebagh passage area and the upper Terranora passage islands.

This species bites most actively around the half moon period.

3. Culicoides longior

This species breeds under tree cover, usually amongst heavy fibrous muds, between mean high water neap and mean high water spring tide zone.

The Tweed River islands are the major breeding source for this species, particularly on parts of Ukerebagh and Womgin islands. Culicoides longior will travel in excess of 1km from its breeding areas. This species is the major pest around West Tweed Heads and parts of South Tweed Heads.

Culicoides longior bites most actively during the week leading up to new and full moon.

4. Lasiohelia townsvillensis

This species is thought to breed in forested areas amongst moist decaying leaf litter and other organic matter following heavy or prolonged rainfall.

The emergence of this midge is generally around a month after major rain events. Nuisance populations of this midge seem to occur when a long dry period has recently been broken by heavy rains. Lasiohelia townsvillensis is often a problem in late spring but may also be a pest at times throughout winter.

Areas often affected by this species are Uki, Chillingham, Tyalgum and parts of Murwillumbah.

Urban green houses can produce localised lasiohelia problems by providing continuous moist conditions and plenty of decaying organic matter. It appears that areas landscaped with bark chips and well watered may also contribute to lasiohelia breeding at times.

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How To Reduce Biting Midge Annoyance

Following are some suggestions to help alleviate or minimise midge problems.

• Keep vegetation surrounding the house to a minimum. This reduces insect harbouring areas and increases air flow surrounding the house. Also keep lawns well mown as any activity that reduces sheltering sites and lowers humidity surrounding the house will help to deter midges. Landscaping with tallish vegetation with an upper tree canopy is preferable to low, dense vegetation in midge prone areas as it allows a much better airflow near ground level.

• If biting midge are a problem entering through fly screens, smaller mesh sizes such as found in products like "Solar mesh" should stop entry. Screens can also be sprayed with the newer low toxic surface sprays containing synthetic pyrethroids to deter midge entering.

• It is most likely that midge will enter dwellings on the leeward or sheltered side of the dwelling. Close leeward windows or keep openings small when midge are a problem.

• As midges do not like to seek blood meals when a moderate breeze is blowing, ceiling fans or other air circulation devices that increase air flow inside the dwelling may also decrease biting midge nuisance indoors.

• Mosquito coils or plug in insecticide tablet burners may be necessary during periods of severe midge nuisance.

• Activities such as water hosing and digging soil attract biting midge. Avoid outdoor activities like car washing and gardening during the early morning and late afternoon when midge are most active.

• As biting midges are biologically linked with the lunar cycle, take note of the lunar period when midges are most active in your area. If for example you live around a canal estate you will most likely be affected by Culicoides molestus. This species bites most actively in the few days following the full and new moon, so planning an evening barbecue around this time during the warmer months would not be wise.

• Wear light long sleeve clothing when outdoors during midge activity periods to minimise exposure to these insects. Personal insect repellents applied as directed usually give several hours protection. Sensitive individuals or young children not wishing to use commercial repellents can try liberal applications of baby oil or Avon skin so soft to exposed skin to reduce bites. An effective home repellent can be made up with equal parts of baby oil, Dettol and an aromatic oil such as citronella or lavender. Local research has shown that oil extracted from the lemon scented gum Eucalyptus citriodora is also a good midge repellent.

• Biting midge have a histamine like substance in their saliva which can cause intense itching in sensitive individuals. To prevent acute allergic reaction and allow the body to develop its own immunity to midge bites vitamin B1 (thiamine) can be tried. This vitamin has an anti-histamine type action. Biting midge expert, Dr. Eric Reye, suggests an adult dose of 200mg twice a day with meals, preferably starting 2 weeks before exposure to midge. As immunity is developed this dose can be reduced. The development of personal immunity generally comes with a regular exposure to low numbers of midge bites, not occasional heavy exposure. Persons who have a more acute reaction to midge bites may require anti-histamine drugs at times.

• Insect trapping devices using ultra violet light as the attractant are generally useless for decreasing biting midge numbers in suburban yards. Traps using carbon dioxide as an attractant must be well designed and operated as well as strategically placed to have any possible beneficial effect.

• Synthetic pyrethroid barrier sprays, applied around vegetation and exterior walls may substantially reduce midge adult numbers around treated premises for many weeks.

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What Is Tweed Shire Council Doing About Biting Midge?

This council has been carrying out research and control work on biting midge since 1981. The following midge related activities are carried out by Council’s Environment and Community Services Division.

• Midge monitoring Biting midge larval numbers are monitored monthly at set points along canal estate beaches. Population data is used to time effective larvicide treatments and to judge the effectiveness of these treatments. The midge larvae are collected in a series of 1litre sand samples taken between high and low tide levels. The sand is mixed with a slurry of molasses and water to float the midge larvae from the sand. Midge larvae mixed in the slurry are then poured through a series of sieves to extract them to be identified and counted. The following graph illustrates midge numbers in 2005 compared to long term averages in the lower river canals.

• Midge larval control Biting midge larvae are controlled with a larvicide several times per year along artificial beaches of the Shire’s canal developments. Treatments are timed to have the biggest impact on midge adult numbers for the least number of chemical applications. Treatments are usually carried out in July and December. The July spray is timed to take out a maximum number of midge larvae before the big spring emergence of adult midge. This treatment leads to less early spring midge attack on residents and a delay to build up of midges over the early summer period. The next treatment is usually in December and is timed to reduce the impact of the second generation of summer midges. This gives relief from the very high midge populations which would normally emerge mid to late summer.

Monitoring midge larval numbers in the canals pre and post-spray over the last 10 years, has indicated midge larval reductions averaged 93% by 48 hours post-spray.

As well as monitoring midge larvae, sand samples are sieved to evaluate non-target safety to crustaceans following spraying. Although crustacean numbers are extremely variable on canal beaches, particularly following canal sand replenishment dredging, there does not appear to be any statistical difference in crustacean numbers pre and post-larvicide treatment.

• Potential biological control Biting midge larvae have been screened in Council’s laboratory for signs of naturally occurring diseases and parasites which may be of use for biological control of midges. During 1994, canal breeding midge larvae at Tweed Heads were found to be sometimes infected with a fungal disease which caused death of the larvae within a few days. This fungus was isolated and sent to insect pathology specialists in Australia and the United States. The fungus was identified as Lagenidium giganteum, a species of fungus more commonly known as a pathogen of fresh water breeding mosquitoes. This was the first record of the fungus attacking estuarine breeding biting midges anywhere in the world. At times the fungus can be quite infective, The average monthly midge larval infection rates at four canal sites varied from 1.2% to 33% during 1994. The Endless Summer canal had infection rates as high as 100% during August 1994. Studies to link the disease rates with salinity, larval density and water temperature did not correlate. It seems the fungus is generally present in a small percentage of Tweed River canal breeding midge larvae and may become very active when unknown environmental effects trigger it. It would be very useful to know these environmental triggers.
       

• Habitat control Council has spent over 10 years investigating the possibility of removing the midge breeding layer from a large river sandbar off Banora Point. Many State Government Departments and private consultants have been involved in this process due to the important biological nature of the sandbar. Unfortunately it looks like the opportunity may have passed to carry out this work as the area is now rapidly being colonised by mangroves. This will reduce the breeding of one midge species but increase that of another. Unfortunately mangroves decrease the favourability of the bar for wading birds, yabbie breeding, fish hauling and seagrass beds. It was the concern for maintaining these assets that made the approvals process so prolonged.
       

• Planning Development plans submitted to Council for sites close to biting insect breeding areas, or which may create biting insect problems, are forwarded to Council’s Entomology Unit for suggestions. A Development Control Plan (DCP 25) relating to biting insect problems in the Tweed Shire was adopted by Council in 1993. The DCP outlines biting insect nuisance, gives suggestions to avoid biting insect problems and includes maps of biting insect breeding areas. A little time spent in the planning stages of development can avoid long term biting insect nuisance problems and health risks for residents and visitors.

References and Further Information

Tweed Shire Council: 02 66702400

American Mosquito Control Association:  http://www.mosquito.org

Department of Medical Entomology, University of Sydney: http://medent.usyd.edu.au/fact/fact.htm#mosquito