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organic rice is nice
From the International Congress of Ecology
IE 2002 - Day 3 - Thursday 15 August 2002
Organic rice is twice as nice
Investigator: Dong-Kyu Lee
Thursday Aug 15th, 2002
by John Bonner
Growing rice by organic methods is not just good for the environment,
according to Korean researchers. Avoiding pesticides in paddy fields
encourages certain fish, which effectively control mosquitoes that
spread malaria and Japanese encephalitis.
Dong-Kyu Lee of Kosin University in Busan, South Korea, described the
results of a study comparing the ecological effects of cultivating rice
by organic and conventional methods. He counted the actual number, and
relative abundance, of the aquatic insects found in both types of paddy.
As expected, the paddies in which no insecticides were used had a richer
variety of insect life. But the actual numbers of larvae of two species
of mosquitoes, Anopheles sinensis and Culex tritaeniorhynchus, were
significantly lower in the organic sites, Lee found.
The former is the main vector species for malaria in the region, while
the latter transmits the potentially fatal viral infection, Japanese
Lee suspected that the larvae were being eaten by a small fish, the
muddy loach Misgurnus mizolepsis, which was much more abundant in the
insecticide-free fields. So he examined the fish's effectiveness as a
biological pest-control agent.
When placed in tanks containing 1200 larvae of both types of mosquitoes,
the tiny fish were voracious predators, Lee found. The fish ate an
average of 1121.8 larvae in 24 hours, and 1195.8 larvae within 36 hours.
The fish showed a slightly higher predation rate on Culex mosquitoes
than on Anopheles, but "muddy loach are effective biological control
agents for both vector species," Lee said.
Lee's findings have convinced the Busan local authority to try and use
the fish to control mosquito larvae living in small ponds and ditches
within the municipality. The fish is not the only form of biological
pest control that his research suggests could be effective.
Lee's work studies show that the king snail, an aquatic species, would
be just as effective as herbicides in controlling the growth of weeds in
the rice crop.
The snail is not native to the area, having been originally imported
from South America. However, there is no risk that the snail could
itself become a pest because the mollusk is not hardy enough to survive
the ferocious Korean winter. Rice farmers wanting to use the snails in
their fields, Lee said, would have to buy a fresh supply of snails each