Effect of Rice Culturing Practices on Seasonal Occurrence of Culex tritaeniorhynchus (Diptera: Culicidae) Immatures in Three Different Types of Rice-Growing Areas in Central Japan

Seasonal occurrence of Culex tritaeniorhynchus Giles immatures was surveyed, together with detailed observations on the rice cultivation practices, weekly in three different types of rice field habitat from 1982 to 1985. Despite early water introduction and seedling transplantation, a late seasonal peak of density and abundance of first instars were observed at terraced rice fields (YE) with continuous water in- and outflow through sluices in a hilly area. In contrast, immature populations increased quickly in flat rice fields (AN, SK). High density and abundance of fourth instars were encountered before midseason drying in rice fields (AN) with less flow and little loss of water, because of construction of an independent irrigation and drainage system. The midseason drying and the alternating flooding and draining after the drying effectively suppressed the occurrence of immatures. Early final draining for harvesting eliminated mass production of mosquitoes, even if the density was high in some rice fields. Differences in timing of seasonal rice-culturing procedures and water management were assumed to be effective in controlling the seasonal occurrence of C. tritaeniorhynchus.