PHOTOPERIODIC CONTROL OF DIAPAUSE 



Table IV. Inductive Cycle Requirement" 



611 



" Experiment 8: number of cycles indicates consecutive 13-hr photo- 

 periods given, followed by llj^-hr photoperiods for remainder of ex- 

 periment. 



Experiment 9: 13H-hr inductive photoperiods followed by 11-hr 

 photoperiods for remainder of experiment. 



live cycles. Fatalities were high in Experiment 8, but the results of 

 another experiment (Experiment 9) were confirmatory. From to 20 

 consecutive inductive cycles (13Vi-hr photoperiod) were given, and 

 then the midges were returned to noninductive conditions (11-hr 

 photoperiod). Results in Table IV show that in this case no pupations 

 occurred until 14 cycles had been given; 14 to 19 such cycles result in 

 only a few pupations, while 50% pupation was obtained in the 

 20-cycle group. 



In these experiments, the response once triggered went to comple- 

 tion in spite of subsequent short days; if an insufficient number of 

 cycles was given, diapause was maintained. Pupation occurred up to 



