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They worm out of bags, onto branches or leaves and follow the smell of their enemies. Like a squad of soldiers, they patrol around, watching out for each suspicious "sponger". Once the parasite is spotted, they will either fight single-handed or besiege it until they win the "fratricidal war".

In this "mite-on-mite" war between amblyseius Cucumeris, a predator mite, and a couple of pests in an orchard or a crop field in spring, the troop of predator mites sweep to victory.

Behind the insectivores stands a woman "commander" Zhang Yanxuan, a professor at Fujian Academy of Agricultural Science, who has spent more than 20 years leading a research group to develop ways to reduce the use of pesticides in more than 20 kinds of plants and crops across China.

The State-funded research program just passed a final inspection earlier this month.

In 1996, Zhang introduced amblyseius Cucumeris, a mite known to prey on a type of small pest, to the country from the United Kingdom and New Zealand. An early experiment on this predator mite in 1997 indicated that it could be trained to devour the mites pestering bamboos.

"We furthered our studies into additional 20-odd plants and crops including citrus, tea, apple and cotton, and were excited to find that it can prey on more than 20 pests, such as spider mites," Zhang says.

Their studies also showed that the use of predator mites could help reduce, by at least half, the use of pesticides for a savings of up to 70 percent.

The professor and her colleagues explored ways to breed and store these predator mites in a large and collective scale, and to transport them safely afar, laying a good foundation for a wide application of these mites in the country. "We worked out of a unique formula to feed these mites so that they can maintain a good level of propagation," Zhang says.

In 2005, the professor established a company, the first one in the country that runs a real biological control business. Today, it sells millions of bags of predator mites to more than 20 provinces, autonomous regions and municipalities each year, with an annual revenue of 2 to 3 million yuan ($265,000-400,000).

It is a huge success, and also a rare one in the field of biological control application, for which Chinese people have known for centuries.

In Nan Fang Cao Mu Zhuang (Flora of South China), a scientific classic about 80 species of vegetation completed in 304 BC, a "red-yellowish ant larger than normal ants" was depicted as being used by fruit farmers in South China as natural enemies to protect citrus fruits from insect damage.

The "ant" in description was a type of weaver ant, Oecophylla smaragdina, living in tropical Asian places. Its application to control pests was later spread to other Asian countries, particularly Vietnam and Australia and expanded to other agricultural plants.

And today, the weaver ant is also becoming a popular scientific topic in these countries, as well as in Africa. In China, where the method originated, relevant studies have stalled because of its limited market potential.

Chen Hongyin, director of the Sino-US Biological Control Laboratory, says that no one in China has figured out how to breed tropical ants in an industrialized scale. "In this case, it won't be a feasible solution," he says.

Despite the widely accepted fact that biological control is the best and most environmentally friendly method of agricultural management, the majority of relevant technologies still remain a topic of discussion in laboratories around the world.

In addition to the difficulty of large-scale breeding, the question of how to store and transport these "biological bullets" is another obstacle that a large number of scientists have been attempting to overcome for decades.

"They are not objects, they are living creatures that can move, escape and die," Chen says.

Zhang recalls an effort to transport ants to the Xinjiang Uygur Autonomous Region in 2004 that failed and resulted in the suffocation of 70,000 bags of predator mites on the train. "Now we use refrigeration to help maintain the temperature and keep them alive, but surely the cost shoots up," she says.

But the biggest barrier facing the development of biological control technologies are farmers. They are accustomed to using pesticides and lack training in the proper use of these natural enemies.

When Zhang tried to promote the use of predator mites in Fujian's rural places, many farmers gave her a cold shoulder. "Once, a farmer promised to test some bags of mites on his orchard. But I discovered that he threw them away right after seeing me off. That was a painful experience," she recalls.

"Farmers don't place trust in these mites. Moreover, pesticides take effect more quickly." 

Opposition from pesticide vendors is also playing a strong role in preventing farmers from embracing biological methods.

Even for those farmers who agreed to use the mites, they were not pleased with the experience at the beginning.

Chen points out: "The cost for biological control is lower, but farmers need to do it right, otherwise, they won't gain the benefits but only see it as a waste of time."

Take the introduction of predator mites into a citrus orchard as an example. Usually, in one citrus orchard there are more than 800 pests that start to wreck havoc in early spring. In the ecosystem, natural enemies are usually born about two weeks later than pests, but are fewer in number.

A lot of farmers have little knowledge about it, so they spray pesticide as soon as they see pests thriving. As a result, they kill the infants of their natural enemies at the same time.

So, according to Zhang, farmers should release the man-raised natural enemies during the two-week intermission to remedy the biological time lag. "In this way, the biological control can be most effective, and the ecosystem can also be repaired," she says.

"What we can do now is to give farmers all the knowledge they need."

Today, Zhang's company has support from local governments and agencies that help her to obtain business.

(China Daily July 30, 2007)