Abstract
During the last three decades a number of investigations have been made on the egg production of mosquitoes, particularly in relation to the habit of hibernation ; nevertheless the results hitherto reported are so diverse with respect to different species or even the same species that it is considerably difficult to make any generalizations. Although some of the early controversies have been settled by the discovery of ecological races, there still remain confusions based on the intricate nature of diapause which may intervene in the life cycle of a certain generation. In such species of mosquitoes as entering hibernation in the adult stage, the diapause state, if it exists, should be characterized by spontaneously arrested growth of ovarian follicles. This general conception on diapause, however, rarely serves for practical use, because female mosquitoes as a rule require a blood meal for developing their ovaries, thus masking the activity of follicle growth with the more subtle changes involved in the activity of blood-sucking. Up to the present time there has been found no convincing explanation of the relationship between these two kinds of activity.
The diapause state in imagines may be detected with less difficulty in some Anopheline mosquitoes, in which the ovaries can develop to the second stage (of Christophers) without a blood meal, as long as the mosquitoes are active (Mer, 1936) . Culicine mosquitoes usually are not endowed with such a convenient characteristic, so that the growth activity of follicles is hardly determinable in those females which have refused to feed on blood, as is commonly observed in cold seasons. No artificial food has hitherto been found which is sucked by hibernating females as easily as fruit juice or sugar water and is yet capable of replacing the part played by the blood meal.
The work to be reported here was commenced with the aim of elucidating the cause of temporary gonotrophic dissociation which was observed by the author in Shanghai Culex pipiens pallens Coquillett (Hosoi, 1944) . Since there was no record which dealt with hibernation of this subspecies from the point of view mentioned above, and it seemed unsafe to generalize the knowledge obtained with European type-species, the larger proportion of the experiments was inevitably occupied with recapitulation of the former work. The work was started at the Shanghai Science Institute, but the largest part of the recent studies was performed at the Zoological Institute of the Tokyo University. Several supplementary experiments were conducted also at the Biological Laboratory of the Tokyo Institute of Technology. The investigation was supported in part by a Grant-in-Aid for Scientific Research, Ministry of Education.
I wish to take this opportunity of expressing my profound indebtness to the late Dr. T. Goda for the permission to work at his laboratory and for his constant encouragement. Thanks are also due to Dr. J. C. Dan for her help in preparation of the manuscript.
