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$604.6
million).
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 8,000 different 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 50 million bethyloids and other parasitic insects.
In
2001, the center released some 38 million 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 1998 after 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 outskirt 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.
(Xinhua News
Agency April 28, 2002)