し尿浄化そうに発生する無吸血生殖性チカイエカの季節的消長について

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In order to observe the seasonal prevalence of the larvae and some morphological characteristics of the imagos of a Culex mosquito in four septic tanks in an urban area of Yokohama City, field and laboratory studies were carried out through the year of December 1962. By the weekly sampling method, a seasonal trend of the larval population could be demonstrated as follows. From the begining of the investigation in early December, there was a gradual decline of the population and this tendency could be seen until February or early March of the next year. The minimum larvae were present during the long period from March to mid June. In late June or early July, the larvae increased rapidly and showed the first peak at the middle of July. After the rapid diminution, the larvae increased again and in late August or early September, they reached the maximum of the year. Since this period, however, a gradual diminution of the population continued to the last sampling which was carried out in December 1963. Through an analysis of the composition of the population in these septic tanks, any stages of the mosquito including the imago was found to exist even during the coldest season from the middle of January to the middle of February. However, in the following spring season from March to May, there were found only insects except for the eggs and younger instar stages. Seasonal difference of the population size was not detected in the case of the samples collected in the septic tanks which were situated at an air-conditioned building. The mosquito was identified as Culex pipiens molestus from the DV/D values of the adult male genitalia. Judging from the seasonal change of DV/D value, the population was monopolaised by Culex pipiens molestus ; it had genetically high uniformity. Water temperature in the septic tanks was warmer than the air temperature in winter but the relation was the reverse in summer. Recorded water temperature ranged from 5℃. (January) to 26℃. (August). The seasonal changes of some chemical properties of the foul water examined seemed to have no relation to the seasonal prevalence of the mosquito larvae. The pupae collected from the septic tanks were bred successively without blood meal. Nine generations were reared throughout the year under the laboratory conditions. The developmental periods which was necessary to complete one generation varied widely according to the seasons. The average developmental period recorded for the nine generations ranged from 16 days, at 25℃., (during September) to 84 days, at 10-15℃., (from ending of November to middle of February). It has been recongnised that the seasonal difference in number of eggs oviposited by a female and the rate of hachability were relatively small. It may be considered that the seasonal prevalence of the mosquito larvae in the septic tanks was affected directly by the following three factors, duration of developmental period of the generation, mortality of the larvae and rate of emergence.
日本生態学会の論文
1967-06-01

し尿浄化そうに発生する無吸血生殖性チカイエカの季節的消長について

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