WASHINGTON ( 2009-01-03 01:12:12 ) :Old mosquitoes usually spread disease, so Australian researchers figured out a way to make the pests die younger – naturally, not poisoned.

Scientists have been racing to genetically engineer mosquitoes to become resistant to diseases like malaria and dengue fever that plague millions around the world, as an alternative to mass spraying of insecticides.

A new report on Friday suggested a potentially less complicated approach: Breeding mosquitoes to carry an insect parasite that causes earlier death. Once a mosquito encounters dengue or malaria, it takes two weeks of incubation before the insect can spread that pathogen by biting someone, meaning older mosquitoes are the more dangerous ones.

The Australian experts knew that one type of fruit fly often is infected with a strain of bacterial parasite that cuts its lifespan in half. So they infected the mosquito species that spreads dengue – called Aedes aegypti – with that parasite, breeding several generations in a controlled laboratory.

Voila: Mosquitoes born with the parasite lived only 21 days – even in cozy lab conditions – compared to 50 days for regular mosquitoes, University of Queensland biologist Scott O’Neill reported in the journal Science.

The study funded by American billionaire Bill Gates Mosquitoes tend to die sooner in the wild than in a lab. So if the parasite could spread widely enough among these mosquitoes, it “may provide an inexpensive approach to dengue control”, O’Neill concluded.