WASHINGTON (AP) _ Genetically modified mosquitoes failed to compete well with their wild cousins in lab tests, complicating efforts to battle malaria by breeding mosquitoes that are unable to spread the disease.
Researchers last fall announced the complete mapping of the genes of the parasite that causes malaria as well as the mosquito that carries it, a step they hope will lead to new ways to combat the ancient scourge that kills 2.7 million people annually.
Among the possibilities is genetically modifying mosquitoes so they are unable to carry the disease, and then releasing them to breed with wild mosquitoes and spread those modified genes.
But when researchers at Imperial College of London tested the idea by inserting easily traceable genes in anopheles mosquitoes _ the kind that spread malaria _ the new genes became depleted and disappeared within 16 generations.
The findings, reported in Friday's issue of the journal Science, emphasize the need to ensure the fitness of the modified mosquitoes. The team led by Andrea Crisanti said scientists might need to release larger numbers of the mosquitoes.
The London mosquitoes weren't actually given genes that would prevent them from carrying malaria, but were given traceable markers that would also be used to keep track of mosquitoes that have been modified to prevent spread of disease.
When the modified mosquitoes were allowed to freely mate with wild insects, the share of mosquitoes carrying the modified genes declined rapidly in subsequent generations, indicating a loss of their ability to compete with the wild mosquitoes, Crisanti said.
The major problem, she said, seems to be that the each group of modified mosquitoes originated with a single insect that was subsequently crossed with its offspring.
``The fact that all individuals in each line are identical is the major disadvantage,'' she said, suggesting that the problem might be reduced by breeding the transgenic insects with wild mosquitoes before release.
Frank H. Collins, a mosquito expert at Notre Dame University, wasn't surprised by the finding that the gene altered mosquitoes didn't compete well.
``I'm not sure the paper really points out anything unexpected,'' Collins commented. ``It points out that there are concerns with fitness (of the mosquitoes) ... but those are concerns people already recognized.''