URUMQI - Forestry scientists have released 800,000 wasps into Asia's largest wild fruit forest this summer, hoping they will kill many of the beetles threatening it.

"It's the fourth time we have released parasitic wasps to destroy the insects eating the apple trees. The measure has so far proved very effective," said Wang Zhiyong, researcher at Chinese Academy of Forestry.

The wild fruit forest, covering 144,000 mu (9,600 hectares), is located on Mount Tianshan along the Ili River valley in the country's far western Xinjiang Uygur autonomous region. Having a wide variety of apple trees, it is also one of the world's largest wild apple gene pools.

The forest has been suffering fruit yield declines since the 1990s, when apple seedlings from east Shandong province that carried Agrilus mali, a type of jewel beetle that feeds on the trunks of apple trees, were planted in the area.

Pruning and spraying pesticides failed to dent the population of Agrilus mali who had no natural enemies in the area.

More than 54,000 mu of fruit trees had been damaged, and more would wither if the pest continued to reproduce, according the forestry bureau of Kazak autonomous prefecture of Ili.

In June 2010, experts introduced parasitic wasps for the first time. So far, 2.2 million wasps have been released into the forest.

The wasps lay eggs on the beetles after killing them, and their larva can later feed on the dead bodies, according to experts.

They said although at the testing stage, the measure has already yielded positive results.

"We are very surprised to find that the wasps have survived two freezing winters in the forest. This means the high-altitude forest can be a new habitat for them," said Wang.

China's forestry scientists have used parasitic wasps to curb the spread of the pests. The forestry bureau of the autonomous prefecture has also used wasps successfully to solve a beetle problem on the south bank of the Ili River.

"We will continue to test the measure for three more years. If the measure can successfully solve the pest problem in the wild fruit forest, it can be adopted in other parts of the region," said Wang.