586 



PHOTOPERIODISM IN INVERTEBRATES 



PHOTOPERIOD AND DIAPAUSE 



The total cessation of growth or reproduction (diapause) is one of 

 the most striking characteristics of dormant insects. It is now clear that 

 photoperiod is one of the most important factors in the environment 

 concerned in the induction of diapause (Lees, 1955, 1956). Although 

 low temperature is often the sole agency responsible for terminating 

 dormancy, this is not always true. In the moth Dendrolimus, for ex- 

 ample, the hibernating larvae remain photosensitive and resume feed- 

 ing and growth at any time in response to the appropriate photoperiod 

 (Geyspitz, 1949). The many species of arthropods known to have a 

 photoinduced diapause include many Lepidoptera, the Colorado beetle 

 Leptinotarsa (de Wilde, 1954; Goryshin, 1956) and the red mite 

 Metatetranychiis (Lees, 1953a). It is worth noting that all these 

 species feed on plants; it is perhaps for this reason that they require a 

 particularly accurate and repeatable seasonal "timetable." 



The direction of the response is the same in nearly all species: long 

 days (or permanent light) cause uninterrupted development while 

 short days of 8 or 12 hr initiate diapause (Fig. lA). This uniformity 

 in the response is hardly surprising since the usual ecological require- 



Photoperiod, hr. per u hr. 



Fig 



1. The induction of diapause by photoperiod. A, the mite Meta- 

 tetranychus ulmi (from Lees, 1953a); B, the silkworm Bombyx mori 

 (from Kogure, 1933). 



