SYDNEY 29 May 2006 - Those annoying blowflies are set to worsen as they morph into 'superblowies', unconquerable by the traditional can of spray.

Carol Hartley, a Postdoctoral Fellow at Australia's research agency, the CSIRO found that blowflies not only had resistance to insecticides from pre-existing genes but they also developed new genetic mutations to resist chemical attack.

Delving into the dusty archives of the Australian National Insect Collection, Hartley sourced DNA from the legs of 70-year-old blowfly samples. "This allowed us to compare DNA from before pesticides were introduced, to modern day flies which have been exposed," said Hartley. "This study provides evidence for pre-adaptation which hasn't been done before."

Pre-adaptation is when an organism uses an existing trait to deal with a new and unrelated situation. In this case, it was found that blowflies had a pre-existing gene, which gave them an inadvertent resistance to a particular insecticide.

The study, a joint venture of Australian, New Zealand and British researchers, examined blowfly resistance to the insecticides malathion and diazinon. "We looked at both the Australian sheep blowfly, Lucilia cuprina, and its close relative L. sericata, and the results were really interesting," Harley said. "We found diazinon resistance in both species but only in present day populations which are still exposed to diazinon. We didn't find any diazinon resistance genes in the 'old' fly legs."

This showed that evolution had occurred since the introduction of the insecticide diazinon to Australia over 50 years ago.

Resistance to malathion, however, was a different story. The team found the DNA of both the modern and 'old' blowflies contained the gene responsible for resistance, supporting the theory of pre-adaptation.

Understanding resistance allows researchers to predict the way in which insects might react to insecticides, a huge bonus considering they develop resistance almost a fast as new insecticides are produced.

Not just a summer annoyance, blowflies are also a serious health problem for sheep, which costs the Australian sheep industry over A$100 million in treatment and loss of stock.