Effect of two rice culture methods on the seasonal occurrence of mosquito larvae and other aquatic animals in rice fields of southwestern Korea.

An ecological study has been performed on the community structures of aquatic animals and on abiotic factors in organically and conventionally-farmed rice fields at Bulkyo, Bosong-gun, Chollanamdo during the rice growing periods between May 1995 and October 1996. The total numbers of aquatic insect taxa in these fields were 25 species, 22 families in 10 orders. In 1995 and 1996, three and then four more species of aquatic insects were collected in the organically-farmed rice fields than in conventionally-farmed rice fields. The common dominant species in both rice fields during the rice cultivation period was Chironomus sp. The abundance of two vector mosquitoes, Anopheles sinensis and Culex tritaeniorhynchus, was lower in the organically-farmed rice fields as compared to the conventionally-farmed rice fields. The populations of mosquito larvae in the organically-farmed rice fields might have been influenced by Chinese muddy loaches, Misgurnus mizolepis. Coefficients of correlation between Chinese muddy loaches and abundance of mosquito larvae showed negative correlations in An. sinensis (-0.66) and Cx. tritaeniorhynchus (-0.47). The average of the species diversity index for organically-farmed rice fields was almost twice (0.62) as much as is of conventionally-farmed rice fields (0.35). The average community similarity between both types of fields was very low (0.33).