Town "oases" support fruit flies

Bernie Dominiak of NSW DPIsays town irrigation generates a favourable environment for Queensland fruit flies.
Bernie Dominiak of NSW DPI says town irrigation generates a favourable environment for Queensland fruit flies.

A study on the presence of the Queensland fruit fly in regional NSW has supported the current strategy of focusing control measures on towns.

The study found that urban environments in regional Australia are warmer and more moist that adjacent rural areas – and that town irrigation plays an important role in ensuring the Queensland fruit fly (QFF)’s survival.

According to an article in the August issue of the Australian Journal of Experimental Agriculture, the combination of increased temperature and more available moisture supports fruit fly populations.

NSW Department of Primary Industries fruit fly Project Coordinator, Bernie Dominiak, said the study was undertaken using computer models and town water use figures.

“We found that moisture appears to be the primary determinant for the number of QFF in NSW.

“Other factors being favourable, a relatively high population would survive with a mean monthly rainfall of greater than 48mm. However rainfall is rarely this high in inland NSW.

“In fact, much of the summer season is too dry to sustain the fruit fly population, unless the environment is modified.”

The researchers found that urban irrigation was a major factor in generating favourable environments for the fruit fly.

“A lack of greenness is the dominant feature of the inland Australian rural landscape in summer.

“However in the urban centres, house owners and municipal councils maintain greenness by irrigating.

“In rural centres, almost the entire summer season becomes favourable for the build up of QFF, even when there is minimum urban irrigation.”

The authors proposed that towns act as oasis for QFF survival, and are surrounded by drier areas “where QFF survival is highly unlikely.”

In most of rural NSW there are large towns interspersed with small towns every 50 to 100 kilometres.

Previous research shows that QFF are unlikely to fly more than a kilometre  and hence do not fly freely from town to town.

Mr Dominiak said ”the town-oasis theory supports the current strategy of releasing sterile flies only in towns and associated orchards.

“Eradication programs in towns with low urban irrigation may be more successful than in towns where more irrigation is used.

“Also, towns with a population of less than 10,000 will have smaller urban heat islands than larger towns and hence provide less heat for the QFF.

Mr Dominiak said the Fruit Fly Exclusion Zone, which operates in NSW, Victoria and South Australia, “seems based on a sound climatic premise for as long as the oasis and desert principle is in place”.

He added that the “user pays” trend, which is increasing the cost of water to consumers, is likely to result in urban dwellers reducing their water use.

“It seems likely that the trend towards higher water costs in towns is likely to assist QFF control programs in future years”.