Effect of intermittent irrigation on mosquitoes (Diptera: Culicidae) and larvivorous predators in rice fields.

Effect of intermittent irrigation to facilitate rice production on rice-field mosquitoes and larvivorous predators was studied in Saga, Japan. Mosquitoes and associated taxa were sampled by dipping in two rice fields subject to intermittent irrigation and in one rice field that remained flooded throughout the study period of approximately 1 mo. With the onset of intermittent irrigation, larval mosquito (Culex tritaeniorhynchus Giles and Anopheles sinensis Wiedemann) abundance decreased; reirrigated fields were colonized initially by first instars. Abundance of aquatic arthropod predators and larvivorous fish also decreased drastically. Water from irrigation canals was considered to be a major source of recolonization by these predators with limited breeding seasons and longer developmental periods than mosquitoes. Richness (number of taxa) of aquatic insect communities decreased, but the percentage mosquitoes among insects increased with repeated intermittent irrigation. Manipulation of rice fields and associated canals as a whole is essential to rice-field mosquito control by water management.