Studies on Imaginal Diapause in Culex pipiens Complex in Japan

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21℃の温度と8～16時問の範囲の日長とを組み合せた実験条件下で，飼育羽化させた札幌，長崎と鹿児島系のアカイエカの各系統の雌と奄美系のネッタイイエカの雌について休眠蚊の出現を誘起させる臨界日長をしらべた．ネッタイイエカは短日下でも活発に吸血し成熟卵を形成したので休眠はないと思われる．札幌系のアカイエカでは日長が13時間より短いときには吸血しない小型濾胞の休眠蚊が出現したので，13時間は臨界日長と考えられる．長崎と鹿児島系では休眠蚊は12あるいは11時間日長下で出現したので臨界日長は札幌系より短かいことになる．同じ3系統のアカイエカの休眠蚊を高温長日下に移して覚醒させた．札幌系では移してから5日目頃から休眠状態から覚醒して吸血したが，長崎と鹿児島系ではより早く覚醒した．以上のことから日本産アカイエカでも休眠蚊の出現を誘起させる臨界日長には地理的変異があり，北へいくほど長くなるし，また休眠の深さも地理的に変異し北へいくほど深くなることがわかった．アカイエカ群の系統によって休眠性が違っていることは，この群の地理的分化を考える上に重要なことである．Follicular development and feeding activity were examined in unfed females of 3 strains (Sapporo, Nagasaki and Kagoshima) of Culex pipiens pallens and one strain (Amami) of Cx. p. quinquefasciatus, which were reared to adulthood under photoperiods from 8 to 16 hours at 21℃, to examine the geographical variation of the critical daylength for induction of the state of diapause in the females of Culex pipiens complex in Japan. The females of the Sapporo strain had well-developed follicles and a very high feeding rate when the photoperiod was longer than 13 hours. With shorter photoperiods, the females had small undeveloped follicles and a low feeding rate ; thus they were in a state of diapause. In both Nagasaki and Kagoshima strains, the diapausing females appeared at a daylength of 12 and 11 hours, respectively. Thus, the critical daylength varies with the strains, being longer in northern strains than in southern strains. However, Cx. p. quinquefasciatus females were not in a state of diapause even under a short photoperiod of 10 hours. In addition, in 3 strains of Cx. p. pallens the diapausing females were produced under a 10-hour photoperiod at 21℃. After they were exposed to reactivation conditions (photoperiod of 16 hours and 25℃), follicular development, feeding rate and gonotrophic dissociation were examined in the females to elucidate the geographical variation of the diapause of Cx. p. pallens. Most of the females of the Sapporo strain had small follicles, and their feeding rate was low for 1 to 3 days after exposure to the reactivation conditions, but on day 5, the follicles began to develop with an increase of feeding rate, and females became gonoactive. Gonotrophic dissociation was usually observed in the females with low feeding activity for 3 days after exposure to reactivation conditions. On day 5, it became very low with an increase in feeding activity. The females of Nagasaki and Kagoshima strains reactivated more quickly than those of the Sapporo strains. The Kagoshima strain was reactivated the most quickly among the 3 strains. Thus, it is clear that the depth of diapause varies with the strain, being deeper in northern strains than in southern strains. On the other hand, fed females collected in autumn in the field showed a low rate of gonotrophic dissociation and the 1st follicles were in stages IIa and IIb. Individuals with such large follicles were not found in a population of overwintering females. These findings reconfirm that the gonotrophic dissociation does not play an important role in the overwintering ecology of Cx. p. pallens in Japan, that is, the females of this mosquito usually hibernate in the state of diapause without feeding on animal blood.
1988-03-31

著者

上田正勝
長大医医動物

Studies on Imaginal Diapause in Culex pipiens Complex in Japan

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