Ecological studies of Culex tritaeniorhynchus summorosus : III. Comparative studies on the out-door resting behavior of the mosquito

Abstract

A series of field investigations were carried out during the summer of 1967 in a village in Okayama Prefecture on the resting behavior of the adult mosquitoes of Culex tritaeniorhynchus summorosus Dyar, 1920, the principal vector of Japanese encephalitis in Japan. A special type of cubic mosquito net traps (exactly 1.5 meters square in size) were constructed by covering the top and the side walls of frame works with white cloth, with the bottom left open. The traps were set at different times of a day on various types of possible resting places, such as thickets near pigsties, sweet potato fields and rice paddies. A large sucking tube connected with a vacuum sweeper operated by a portable electric generator (Honda Super-watt-300) was used for catching the adult mosquitos from inside of the mosquito net trap, and the population density per 1.5m^2 as well as their composition at certain times of a day in certain resting places was recorded. Laboratory and field studies with other methods were carried out also to supplement the information necessary for estimating the daily rhythm of their activities. As a result, it has been shown that the adults of this species of mosquito are nocturnal in activity as the principle, and take various types of vegetations as their daytime resting places, especially under low and flat leaves of densely growing plants, such as in sweet potato and strawberry fields. The adults were found to emerge from pupae at night with a peak at about the midnight, and the newly emerged males and females mostly stayed on nearby plants at least until the next morning. The mating was estimated to take place on the second night, the blood sucking of females in or after the third night, and the first oviposition during the sixth or the following nights. The females successfully engorged with blood were found to be resting during the night on nearby thickets, but moved to more suitable daytime resting places at dawn such as under leaves of thickly vegetated sweet potato fields. Large numbers of both males and females (including all gonotrophic stages) were found to be resting during the daytime in such a type of vegetations, but most of them flew away into the air after the sunset.