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Groups of bethyloids -- parasitic insects that resemble tiny rice kernels -- are busy flying in the Western Hill poplar forests on Beijing's west outskirts, searching for delicious "meals" of long-horned beetles.
These bethyloids are a type of natural "killer" specially released there by Chinese entomologists to wipe out an increasing numbers of forest insect pests -- mainly long-horned beetles, pine moths and sawflies.
Since the beginning of this spring, approximately 30 centers breeding such biological killers across China have intensified reproduction, aiming to ease the worsening problem of forest pests.
According to experts from China's forest protection departments, long-horned beetles are fatal to the poplars and pines widely planted throughout the country, with their larvae able to drill through the trees' stem and pith.
Since 1990, China has on average 8 million hectares of forests plagued by pests per year. Insect damage to man-made forests has caused an annual economic loss of over 5 billion yuan (US$604.6million).
Chen Changjie, a researcher with the China Institute of Forest Entomology, considers that the fragile forest ecology due to age-old afforestation with single tree species is the major factor behind the growth in pests.
China has more than 8,000different species of harmful insects. "It leaves great scope for their natural enemies to be a power in pest control," Chen said. This year, the Beijing forestry biological control center plans to produce over 50million bethyloids and other parasitic insects.
In 2001,the center released some 38million various natural enemies of forest pests.
Tao Wanqiang, head of the Beijing Forest Protection Station, said that controlling pests with their natural enemies had achieved good results in some trials, including at Western Hill and Daxing District.
"These little insects have a strong ability to hunt for their hosts and produce no negative effects on people, the local environment and other beneficial insects," said Tao.
Recalling the fight against American white moths which once severely damaged the Daxing forests on the southern outskirts of Beijing, Tao said he still felt distressed at the memory of chewed leaves and naked branches caused by the moths.
However, in 1998after natural enemies of the white moths were released into the forests, the trees turned green again and the moths were basically eliminated.
Another Beijing "factory" of such natural enemies located in northeastern outskirtan Miyun County breeds over 50 million trichogrammatids annually, which can be released into more than 333,000 hectares of forests to kill pine moths. Drought-prone Gansu Province, northwest China, has about 173,000 hectares of forests plagued by pests every year. However, prevention measures in the form of spraying pesticides have not saved trees from the ravages of insects.
This year, the local forestry department has embarked on establishing centers to propagate large numbers of the biological enemies of forest pests, in a hope to "control insects by insects. "According to He Fengying, a senior biological engineer with the Beijing Chaoyang Forestry Station, these enemies are the nature's most significant way of controlling harmful insects.
"As well as the instant success of these natural enemies, their offspring also have a long-term positive impact on preventing and controlling the pest plague," said He Fengying.
Though biological means now make up only 15 percent of prevention methods, the control of forest pests --from the universal use of poisonous chemicals to the release of natural killers and other biological technologies --has been quite successful in China.
Nevertheless, experts warn that biological control is just a temporary expedient. The best way to annihilate forest pests is a stable ecological system with a balance between harmful insects and their natural enemies, which depends largely upon multiple tree species and the growth of biological diversity in forests.
(eastday.com April 29, 2002)
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