The population density of mosquitoes in paddy fields for rush grasses was investigated during their growing season, from December, 1963 through July, 1965, at three spots in Okyama Prefecture, Ichinomiya near Okayama City, Bakuro-cho in Kurashiki City, and Chaya-cho.
No mosquito larvae were found throughout the whole term of the study in the rush fields presumably because they usually are watered only moderately and especially from late May to July they are rather dried. The larvae, however, were found in the rice fields and their drainages around the rush fields from early May, and the emerged adult mosquitoes from the larvae migrated into rush thickets during when the stems of rice plants were still short.
Two light-traps were placed in each spot, the one right in the center of the rush fields and the other somewhere apart from them, and the mosquitoes collected were significantly more abundant in the former.
The rush fields is not an appropriate breeding place for mosquitoes and it is likely that rush grasses have provided a suitable hiding habitat to adult mosquitoes.