PHOTOPERIODIC CONTROL OF DIAPAUSE 621 



Lees (1954, 1955, 1956) has reviewed the Hterature on the role 

 of the periods of light and dark in the photoperiodic responses of 

 arthropods and points out that knowledge is insufficient to permit a 

 detailed interpretation of results that have been obtained thus far. 

 Further, our own data are too few to allow a critical comparison with 

 the findings of others; however, one point does deserve mention. In 

 other photoperiodic arthropods, in which night-interruption experi- 

 ments have been conducted, a relatively long period of light is needed 

 to effectively "break" the night. For example, in Metatetranychiis an 

 8-hr photoperiod ( 16 hr of dark) produced 100% diapause, but when 

 an 8-hr light interruption was introduced into the dark period, reduc- 

 ing total dark to 8 hr, diapause dropped only to 62% (Lees, 1953b), 

 The effectiveness of a IVi-hr interruption in Metriocnemiis appears 

 to represent an exception to the pattern that has been established for 

 other arthropods. 



It has been reported in several arthropods that very short photo- 

 periods (with corresponding very long dark periods) and continuous 

 darkness tend to have an effect more or less like that of a long day. 

 This is true in Macrosiphum (Shull, 1929), Diataraxia (Way and 

 Hopkins, 1950). Grapholitha (Dickson, 1949), Metatetranychus 

 (Lees, 1953a), Acronycta (Danilyevsky, cited by Lees, 1955), 

 Antheraea (Tanaka, cited by Lees, 1955), and Barathra (Otuka and 

 Santa, 1955), It appears to hold for every arthropod in which it has 

 been tested except Bombyx (Kogure, 1933). When Metriocnemiis 

 knabi larvae were given continuous darkness for 43 days, more than 

 50% pupated, as compared to 0% in a control group on a 1 1-hr day. 

 This effect appears to be characteristic of most arthropods. Its ap- 

 proach to universality in this group of animals suggests the desirability 

 of investigating the matter in other photoperiodic animals. In birds, 

 for example. Rowan (1938) claims to have obtained complete sper- 

 matogenic stimulation through enforced wakefulness in total darkness, 

 apparently overlooking the possibility that the response obtained 

 might have resulted directly from the action of continuous darkness. 



The present study has attempted to correlate day length changes 

 with seasonal diapause in Metriocnemiis knabi and to determine some 

 of the characteristics of the photoperiodic response. It will serve as a 

 basis for research planned for the future. 



