Spraying ineffective against fever, says CEN

Central Coast Environment Network chairman Mr John Asquith has said that a proposed spraying of wetlands near Hardys Bay with the mosquito control agent Bti would have "little or no impact on the occurrence of Ross River fever".

He cautioned that there had been no long-term studies of the chemical.

"CEN believes more testing has to be done before we can decide that Bti is a safe chemical to put into wetland environments," Mr Asquith said.

Mr Asquith suggested that improving the ecological health of wetland areas was likely to be a more successful mosquito reduction strategy.

Mr Asquith referred to a report released last year called "Living with Mosquitoes on the Central Coast Region of NSW", which was designed to assist local groups including Gosford and Wyong Councils manage the mosquito problem.

"Media articles have referred to possible increases in mosquito-borne diseases such as Ross River virus and dengue as a result of higher temperatures and water levels due to climate change," Mr Asquith said.

"Ross River virus occurs on the Central Coast and is a notifiable disease to health authorities.

"However, the number of notifications on the Central Coast have been much lower than in the Lower Hunter area or the Mid North Coast Region.

"Also, the NSW Arbovirus Surveillance and Mosquito Monitoring Program found that, from January 2002 to January 2007, the 109 cases of Ross River virus that were reported were from residents from all over the Coast and not one particular area.

"This means that spraying Bti onto wetlands will have little or no impact on the occurrence of Ross River fever.

"The monitoring program conducted by NSW Health has not detected any mosquitoes that were carrying Ross River or Barmah Forest viruses.

"Dengue is not a problem on the Central Coast and has so far only appeared in Queensland, where Bti is being used."

Mr Asquith said Bti was a bacterium known as "Bacillus thuringiensis israelensis".

"This bacterium produces a poison which destroys the gut wall of mosquito larvae and kills them," Mr Asquith said.

"Bti is generally sprayed over mosquito breeding sites such as wetland habitats so that the larvae will ingest it and die within 12 hours.

"It is regarded as a 'safe' chemical pesticide and environmentally acceptable because it affects mosquitoes and very few other insects.

"However, long-term studies of the impacts of Bti on our wetland environments, which are quite degraded in some places and under a lot of pressure from development, have not been done to confirm this.

"In terms of the safe use of Bti, its Safety Data Sheet states that people should avoid all direct contact with the product as it may cause irritation to the eyes and skin.

"Protective clothing, an air purifying respirator, impervious gloves and safety goggles should be worn by anyone using Bti."

Mr Asquith said the data sheet also stated that ecological information regarding the effects of Bti had not yet been determined and neither has its chemical stability.

"Of the two most problematic mosquito species on the Central Coast, one is an estuarine mosquito, which breeds in endangered saltmarsh and mangrove habitats.

"The other is an urban mosquito which breeds in small pools of water around houses and other buildings.

"The NSW Health Arbovirus Surveillance and Mosquito Monitoring Program found that the estuarine mosquitoes are most prevalent in the Empire Bay area of Gosford whilst in the Wyong area the urban mosquito is of most concern.

"Spraying of Bti around all residential areas is obviously not an option."

Mr Asquith stated that besides being an environmentally undesirable chemical Bti had "some other drawbacks".

"It is not effective in all wetland areas, and it has to be ingested by mosquito larvae at a certain stage of their development, which means there is only a small window of opportunity to use it effectively," Mr Asquith said.

"Also, Bti needs to be reapplied after each high tide and after rainfall.

"According to the Emerald Shire Council's website, Bti is not very effective when mosquito populations are very high and populations of mosquitoes have been found to rebound from a dose of Bti after only one-two weeks (Dept. of Medical Entomology).

"Aerial applications of Bti, as mentioned in the Living with Mosquitoes report, would presumably inadvertently also cover residential areas in the vicinity of wetlands and would not be acceptable to many residents.

"It should be remembered that mosquitoes are a natural and important part of wetland ecosystems.

"They provide food for many native animal species and play a role in the breakdown of detritus.

"CEN supports a cautious approach in regards to the use of Bti as a form of mosquito control on the Central Coast.

"There may be some isolated cases where Bti could be used effectively.

"However, a range of other protective measures could be more effective, including personal sprays and clothing for protection against bites, keeping containers around the home free of water, having good flyscreens, maintaining healthy wetland habitats so that mosquito breeding does not explode and not building houses close to wetlands."

Press release, 14 Jan 2007 John Asquith, Community Environment Network