Peng Huiyin was recently honored at the 2005 National Technological Invention Awards for his research into insects.

For the past 30 years, Peng Huiyin has been pursuing a hobby that will shame those of us who scream every time we see a cockroach. The biologist looks for dead insects not only at home but also wherever he travels.

Peng tries to look for what killed the insect and if he comes across many dying in the same way, he takes them back to his laboratory for further analysis.

"We have identified dozens of types of viruses that can kill a wide range of pests," said Peng, a leading scientist of biological pest control at the Wuhan Virus Research Institute of the Chinese Academy of Sciences in Hubei Province.

Peng and his colleagues have come up with a unique way to protect crops using parasitic wasps that deliver lethal viruses to crop pests.

Their research results, the world's first, won the second prize at the 2005 National Technological Invention Awards, at the National Science and Technology Congress held in January in Beijing.

Since Peng entered Wuhan University to study biochemistry in 1972, he has been learning of and developing ways to use viruses to kill crop pests.

Virus-based pesticides

Through most of the 1970s, he tried out viruses to kill and prevent pests in cotton and tea fields.

"The idea of using viruses to kill pests is simple and not new, but their efficient practical application has puzzled Chinese researchers for years," Peng told China Daily.

The first difficulty concerns infecting the pests with the virus. Unlike chemical pesticides, which can kill pests by polluting their feed through massive spraying, viruses are alive and have a short life.

"To use a virus-based pesticide, you have to produce a large amount of it. But we certainly cannot produce the viruses as cheaply as chemical pesticides," said Peng.

He admitted that this is a difficulty that is shared by most of the so-called biological pesticides, although they are much more environmentally friendly than chemical ones.

"For example, some viruses are highly specific to certain types of insects and will not infect other types even if the latter are exposed to them long enough," Peng explained.

Although virus-based pesticides have been tried before, their higher costs and lower efficiency compared to chemical pesticides have contributed to their accounting for less than 5 percent of pesticide use in China, according to Peng's estimate.

In the mid 1980s, Peng found a way that signaled a breakthrough in virus-based pest prevention.

"On many occasions, I found that a small amount of viruses caused large-scale deaths in target pests," Peng said.

This meant that scientists could make their method efficient if they could zero in on the right virus for target pests.

Breakthrough

He and his colleagues then went on to study ways of triggering an epidemic among target pests with human cultivated viruses.

"We first proved that the saliva of the infected pests, and then their secretions, and finally their eggs, could work as the media to spread the viruses," he said.

"On some occasions, we found that there might be respiratory contagions among pests, although so far we have not identified the mechanism for this," Peng said.

Peng and his colleagues then focused their efforts on pest eggs. Most insect larvae have a habit of eating their own eggs as their first nutrition after they are hatched. The researchers realized that if the viruses were placed on the eggs, this would cause an epidemic among pest larvae, greatly reducing the risk to crops.

"The question was how to lay viruses on the eggs. You simply cannot collect them in the wild," Peng said.

As Peng and his fellow researchers agonized over this issue, their eyes fell on parasitic wasps.

Parasite wasps

It happened when Peng had come across material describing how parasitic wasps had been used to prevent forest pests in China's northeastern provinces, the former Soviet Union and Canada.

Certain parasitic wasps lay their eggs on other insect eggs. The wasp larvae feed on them, killing their hosts before they hatch.

According to Peng, one of the major difficulties in using parasitic wasps is that wasps are always fastidious in selecting host eggs, limiting their lethal effect.

"But the wasps' fastidiousness in selecting host eggs was just the thing to use to spread viruses to pests," Peng said.

Peng and his colleagues have been engaged in extensive research into parasitic wasps since 1991.

They have found the right types of parasite wasps, the best amount and method of carrying the viruses and the methods to control their birth.

In their studies, they took the parasitized insect eggs and soaked them in a solution containing a virus that is lethal to the pest, but harmless to the wasp. When the wasps' offspring hatched, the virus became attached to their bodies.

Before female parasitic wasps select the right pest eggs to lay their own eggs on, they often crawl over hundreds of pest eggs.

"In this way the virus can be spread to hundreds of pest eggs," Peng said.

After hatching, any pest larvae that have not been parasitized feed on the remains of their eggs and ingest the lethal virus.

Peng said that in 15 years of research, the team had identified more than 20 viruses that kill different pests but not the wasp.

Field trials of the methods have been conducted on more than 13,000 hectares of farmland and forests in China.

Peng said given the high efficiency of the approach, its cost is about 25 percent less than that of chemical pesticides, and is effective against more than 20 insect pests.

Farmers using the method will put the virus-coated pest eggs that contain developing wasps in their fields and wait for the wasps to emerge. The wasps can be tailored to carry a different virus, depending on which pest posed a problem.

"It is very likely to be commercialized within one or two years, after the Ministry of Agriculture checks its efficiency," Peng said.

Ecological pesticides

According to Peng, most biological pesticides, including his, will not kill the natural enemies of pests, such as frogs, birds and wasps, enabling them to play their role in controlling crop pests.

"Compared with chemical pesticides, our virus-based pesticides are not aimed at eliminating the whole pest population over days. While we kill most pests, the natural enemies can help control the others," Peng said.

Different kinds of pests often have common natural enemies. While Peng's specific viruses kill certain types of pests, the target pests' natural enemies can turn to other types of insects.

Currently, biological pesticides cannot replace the broad-spectrum chemical pesticides, because "farmers hope to see all pests die out the day after they spray their pesticides."

But with more strict rules on pesticide traces on crops and fruits, farmers will be forced to turn to biological pesticides.

"This time, it will be a win-win solution for both farmers and the environment," Peng said.

(China Daily February 22, 2006)