A survey on the nature of mosquitoes was made at a pigsty in Kayou Town, Joubou District, Okayama Prefecture. Mosquitoes were collected with three methods i.e. light trap, dry ice-trap, and hand-capture once a week from June 15 to October 15 in 1969. A fluorescent lamp (20 W) was used for the light-trap. A mosquito-net, about 180cm×230cm×190cm in size was used for the dry ice-trap. The light-trap and the dry ice-trap were settled for two and a half hours starting from 30 minutes before sunset. The hand-capture was used to collect resting mosquitoes on the pillars of the pigsty for 30 minutes from 1 hour after sunset. We obtained the following data:
1. Culex tritaeniorhynchus were collected most with any method, and then the next Anopheles sinesis, Culex vishnui, Culex pipiens, and Armigeres obturbans. The ratio of Anopheles sinensis to the other species in number, with the dry ice-trap, was smaller than that with the light-trap or the hand-capture.
2. In the case of the light-trap, the appearance of Culex tritaeniorhynchus and Anopheles sinensis were influenced by the minimm temperature for the collecting time.
3. Male Culex tritaeniorhynchus acts freely when the temperature is above 23°C and female at the lower temperature than that.
4. Concerning the resting mosquitoes collected by the hand-capture, it was the season when mosquitoes appeared most that the number of engorged was greater than that of the unengorged. This phenomenon was clear in Anopheles sinnsis than in Culex tritaeniorhynchus.
5. Some Culex vishnui were collected, but the number was small and the period was short, so it is not so important as a Japanese encephalitis virus vector.
