Pesticides Create Pests, Don't They?

13/12/2011 15:42 GMT | Updated 12/02/2012 10:12 GMT

Since the 1960s we have known that pesticides when used without care and attention will cause insect pest outbreaks. But we never seem to learn. In recent years there have been severe outbreaks of planthoppers and leafhoppers on rice in China, Vietnam and other countries in South and Southeast Asia. It is part of the reason why global rice production has become unstable since 1999. Rice prices have soared as a result.

An international conference on the threats of insecticide misuse in rice ecosystems in Vietnam on the 16th December could not be more timely. But despite all the knowledge and understanding scientists have amassed about this issue, we should be under no illusions that this abuse of pesticides will be easily resolved.

My interest in the pesticide challenge began in the early 1960s when I was appointed the government entomologist in North Borneo (Sabah). On arrival I was immediately sent to the young cocoa plantings near the Indonesian border. There I was confronted by field after field of cocoa without leaves, infested by a variety of insect pests feeding not only on the leaves but on the branches and the trunks of the trees. The farmers said they were doing everything they could, spraying cocktails of lethal insecticides every week, but to no avail.

It occurred to me that perhaps the pests had previously been naturally controlled by their enemies, parasites and predators, which had been killed by the indiscriminate pesticide use. I suggested we stopped spraying. This proposal was met with some derision but my Director of Agriculture backed me and spraying was stopped. Soon parasites and predators appeared and six months later all the pests had come under control, except for one which was treated by a highly selective insecticide.

This was the first example of Integrated Pest Management (IPM) outside California and Peru where the concept had been invented five years earlier. It was highly successful, persisting for several decades.

Soon afterwards I went to visit the International Rice Research Institute (IRRI) in the Philippines. I discovered they were placing cans of insecticides in the water inlets to the fields. I told them they were courting trouble, but they were dismissive.

In the 1970s Asian rice fields were attacked by massive outbreaks of Brown Planthopper, a sucking bug that carries destructive viruses. Losses in Indonesia rose to one billion dollars a year. Then brilliant research by Peter Kenmore and his colleagues showed that the planthoppers were naturally controlled by parasitic wasps and wolf spiders.

The answer was to greatly reduce the use of insecticides. In 1986, a decree by the Indonesian president banned 57 broad spectrum pesticides and a system of IPM was developed. Farmer Field Schools were used to teach farmers about the planthoppers and their natural enemies and when to use insecticides. Soon the average number of sprays per season dropped from over four to one at most. Once again the control was highly successful and persisted.

But with the passage of time the lessons have been forgotten. Since 2004 outbreaks of leafhoppers and planthoppers have occurred in many Asian countries. The 2005 outbreaks were devastating in Vietnam and China. Farmers, under pressure, had reverted to heavy use of prophylactic insecticides. There is not much money to be made from selling rice seeds, even the new hybrids developed by the Chinese, but pesticides are highly profitable. The agro-chemical sellers have combined seeds and insecticides in packages that are proving to be highly destructive.

What is the answer? We need more research, specifically designed to develop IPM systems that allow natural enemies to do their work of controlling the leaf and plant hoppers. We also need to ensure that insecticides are only used when necessary, and compounds are chosen that will not elicit resistance from the pests.

But even more important is decisive governance. Political leaders need to recognise the problem for what it is and to put policies and regulations in place that will enforce IPM and strengthen the desirability of sustainable agricultural systems.

This issue is now urgent. Without immediate action rice production is under threat and without sustained action these problems will be recurring. I hope at the conference this Friday we will prove we have learned from the past.