Abstract
During a period from June to December, 1964, an investigation was carried out on mosquitoes inhabiting in the septic tanks in Kanagawa Prefecture and the results were summarized as follow. 1) In the cases of 1, 315 septic tanks which were widely distributed in Kanagawa Prefecture the mosquitoes were found in 467 of the cases (35.3%). Local difference of the occurrence was little significant. 2) Frequency of the mosquito occurrence in two types of the septic tanks was higher in the modified types than that in the standard type. 3) The mosquitoes were identified as Culex pipiens group, Armigeres subalbatus and Culex kyotoensis. Among them, Culex pipiens group was the dominant inhabitant in the septic tanks and sometimes it was found with Armigeres subalbatus in same tanks. Culex kyotoensis was collected only from two tanks which are situated aside of Lake Ashinoko, Hakone National Park. 4) Concerning problems of Culex pipiens group found inthe septic tanks, the autogeny of adult females and the DV/D ratio of male genitalia were examined. For this purpose, pupae and 4th instar larvae were collected as materials from 33 septic tanks in various localities and cultured during about 10 days in the laboratory condition. 5) According to the features of both autogeny and DV/D ratio, Culex pipiens group found in the septic tanks was able to subdivide into two forms, pallens and molestus. In most cases, the mosquitoes were found in a mixing population of two forms in most of the habitats with its ratio being not constant. In some cases, however, the habitats were occupied by only one of the mosquito, pallens or molestus. 6) It is quite probable that the septic tanks are demonstrating not only a considerable significance as a breeding site of the mosquitoes, but these are also playing an important role on the natural selection from pallens to the molestus-form.
