The Effect of Fish on the Abundance of the Rice Caseworm Nymphula depunctalis (Guenee) (Lepidoptera: Pyralidae) in Direct Seeded, Concurrent Rice-Fish Fields

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Abstract
In the 1996-97 dry season, a rice caseworm (Nymphula depunctalis (Guenee)) outbreak occurred at the Co Do rice-fish experimental station, Can Tho province, Mekong Delta, Vietnam. A polyculture of Thai silver barb, common carp and Nile tilapia was able to reduce the number of rice caseworm larvae (P< 0.001) by at least 93%. As a result, the number of rice caseworm adults (P< 0.001) and the percentage of damaged rice leaves (P< 0.001) were also reduced compared with rice fields without introduced fish. As the pest reduction did not differ in fields with high and low seeding densities, it was concluded that the access of fish into the rice field was not severely hampered by high rice seeding densities. The presence of fish or rice caseworms had no effect on the rice yield. The broader acceptance of rice-fish culture could lead to a reduction of the number of pesticide sprays used against highly visible defoliators like the rice caseworm. This would enforce the concept that rice-fish culture and integrated pest management are complementary.