Die Bedeutung der Tageslänge für das Einsetzen der Fortpflanzungsperiode bei Porcellio scaber Latr. (Isopoda)

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Abstract
The isopod, Porcellio scaber breeds in nature between March and August. An artificial 16 hrs light: 8 hrs dark will raise the QO2, molting frequency and induce breeding in these animals at any time of year. In a period of 7 hrs light: 17 hrs dark the animals remain in the normal winter condition. However, if 2 populations that had been exposed to light from 5 a. m. to 12 noon and from 10 a. m. to 5 p. m., respectively, are exchanged so that population I is now subjected to light conditions II and vice versa, a number of females in each population develops brood pouches and produces offspring. This is explained by assuming that the effects of 2 short light periods of different phase can add up to produce the effect of one long light period. This assumption requires the existence of an endogeneous time keeping mechanism and of a hormone, the production of which is controlled by the photoperiod but has a certain time lag.

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