Asia has a new population crisis -- not in people, but in rats.
The new rice seeds of the ''Green Revolution,'' which helped farmers grow two and three crops a year, also brought with them a multiplying of rats, which gnaw away at harvest yields.
''Rats and other varmints don't have much trouble surviving in Asia these days,'' says Jan H.M. Oudejans, a United Nations pest expert in Bangkok.
Intensive farming with new rice seeds, irrigated fields, and abundant fertilizer use have made more and more of Asia's land green with growth almost year round. Pesty rodents have had a field day, feasting on the steady crops. An acre of rice with over 2,000 rats is considered ''out of control.'' Unlike pre-Green Revolution days, farmers leave few fields fallow for one season, or barren enough to starve out rats and keep their population in check.
''We've gone so much for high yields in rice and other grains that we've ignored the ecological response of pests, especially rats,'' Mr. Oudejans said. ''We took on the biggest threat -- famine -- and now we must deal with the side effects.''
Fortunately for Asian peasants, tricks to catch the dirty rats are also multiplying. The best response is communitywide rat collection. In fact, farmer cooperatives are now forming around the problem of rat control.
Here in Thailand, many villages have organized ''rat days.'' In a celebration atmosphere, for instance, farmers in Rat Buri Province (the name is a coincidence) recently rounded up as many rats as possible and carried them in bundles back home. There the hairy mammals were cooked in a stew and eaten.
In ceremony-rich Bali, a few hamlets with rat problems are known to hold elaborate rituals during which thousands of rats are cremated in templelike structures to appease a Hindu rat god, who, it is believed, will halt the infestation.
In many nations farmers are advised by agricultural agents to remove rice stubble after each harvest. This cuts down on the rats' food supply. Also, farmers are told to rebuild the long embankments of mud that separate irrigated rice paddies so that they are are too thin for rats to burrow tunnels and make a home for themselves. Such tricks are especially encouraged in nations where any taking of life is considered immoral, such as India.
Another antirat technique is the ''floating restaurant.'' These are bowls filled with poison and set to float in irrigated rice paddies. Swimming rats climb aboard and eat their last lunch.
The new high-yielding rice seeds, which were introduced in the mid-1960s, brought other problems. At first, they were susceptible to a worm pest known as a stem borer. Scientists bred new rice varieties with resistance to this pest. In the 1970s, the brown plant-hopper pest hit Asia's paddies, destroying as much as 46 percent of Indonesia's crops in l979. Wherever the tiny insect struck, vast stretches of rice plants turned brown. Other pests, such as the whorl maggot, are now showing up.
''Each new rice variety can be vulnerable to new pests,'' Mr. Oudejans said. In some countries, such as Indonesia, where a single type of rice is used widely , officials fear that a pest could suddenly sweep the nation's crops, bringing almost instant famine. Before the Green Revolution, local rice varieties varied enough in genetic makeup to have differing levels of pest resistance.
To battle pests, today's Asian farmer has become dependent on pesticides, many toxic to humans. The abuses and misuses are many. Women sometimes mistakenly wash their hair with the poisonous substance.
But suicides are an even greater problem. In the Philippines last year, most of the more than 600 people officially listed as killed by pesticides used the poison to commit suicide. And some environmentalists worry about longer-term effects of exposure to the poisons.
''Farmer ignorance is our biggest problem,'' Mr. Oudejans said. Many farmers are illiterate and cannot read instructions on how to spray the chemicals, where to use them, and what kind of clothes to wear.
In 1980, the United Nations began training courses on pesticide use in eight Asian countries (Bangladesh, Burma, Indonesia, Nepal, Pakistan, the Philippines, Thailand, and Sri Lanka). Over 250 instructors were sent to help educate agricultural retailers and agents -- who regularly work with farmers -- on proper handling of pesticides.
About 60 percent of the Philippines' 6,000 agricultural ''technicians'' have taken the UN-sponsored one-day course on pesticides. Cartoonlike posters explaining pesticide use are being passed out to farmers, and a ''farmcasters'' radio program regularly educates farmers on proper use.