Abstract
Changes in the age-composition of a Culex pipiens molestus population at an underground breeding site in downtown of Tokyo were observed from December 1963 to April 1964. Mosquito collections were made with a sucking tube once in a week or two and their ages were determined by counting numbers of relics in the ovarioles. The breeding place is located at the bottom of a building and was observed to be well closed and isolated from outside. Not a single blood-fed mosquito was collected. The population was apparently having been maintained by autogenous proliferation. 318 out of 794 total number of dissected female mosquitos were found parous, however, only 5 among them were biparous and none triparous or over. The development of follicles was observed extremely retarded in the parous mosquitos. The evidences indicated that under the circumstance without blood sources the mosquitos principally laid eggs only once in a lifetime. A period analysis showed that the parous rate fluctuated at 6 week interval. The room temperature was at a fairly constant level from 15°to 20℃ and the temperature of breeding water at 13°to 16℃ during the period of observation. There were no correlation observed between the parous rate and the environmental conditions. So the periodical changes in the parous rate might be interpreted as a result of the periodical reproduction of the population. An exceeding correlation between the parous rates and the mating rates could be observed.
