PHOTOPERIODIC CONTROL OF DIAPAUSE 613 



oiven in this table are the resuUs obtained after 72 days with groups 

 A and B, which had been continued on their original schedule. 



When a short day length occurred only every fifth day in a schedule 

 of otherwise inductive day lengths, the resuhs obtained were similar 

 to those obtained with consecutive long days. It appears that a more 

 frequent occurrence of noninductive photoperiods reduced the re- 

 sponse. Only one larvae pupated in group B (after 72 days), thus 

 indicating a near absence of effectiveness of a regime of long photo- 

 periods alternated with short. 



Dark Period Interruption (Experiments 11 and 12) 



In the experiments described thus far, all larvae were exposed to 

 cycles consisting of a light phase, followed by a dark period, one 

 being complementary to the other and together totaling 24 hr. An 

 insight into the relative importance of each phase — light and dark — 

 can be obtained by departing from cycles having this simple comple- 

 mentary relationship. Two experiments involving night interruption 

 will be described. 



Experiment 11 was conducted to determine whether the period of 

 light making up the difference between a 12- and a HVi-hr photo- 

 period need be continuous with the short photoperiod to be effective, 

 or whether it would be so if given at different times during the dark 

 period. The light regimes and results are given in Table VI. The 

 experiment ran 49 days, beginning January 13, 1956, and utilized 

 larvae collected in North Carolina on December 26, 1955. A 12-hr 

 photoperiod cabinet was not available for the experiment, so an 11 -hr 

 day group served as a short-day control. Ample evidence in other 

 experiments indicated, however, that 11 -hr and 12-hr photoperiods 

 were equally noninductive. Pupations occurred in every group except 

 the 11 -hr day controls, indicating the effectiveness of the added light 

 when given so as to interrupt the dark period. 



Another experiment (12) tested the effectiveness of night interrup- 

 tions when the total amount of light given during 24 hr was less than 

 that required in a normal day-night sequence for induction of pupa- 

 tion. The larvae used were collected December 26, 1955, in North 

 Carolina, and the experiment, begun March 8, 1956, ran for 65 days. 



