PHOTOPERIODIC CONTROL OF DIAPAUSE 605 



intensity at station A was measured with a Model 756 Weston 

 illumination meter; intensities for the remaining stations were calcu- 

 lated by the inverse-square law. The incandescent lamp was shrouded 

 by black cloth in order to minimize scattered light from the walls of 

 the room. The fluorescent lamps and the incandescent lamp were 

 operated bv two different timers: the latter hght source was turned on 

 1 min before the fluorescent lamps were turned off. 



EXPERIMENTS AND RESULTS 



Critical Photoperiods (Uxperiments i, 2, and 3) 



The results of three critical day length experiments are given in 

 Fig. 1 and Table I. Onlv photoperiods near the previously determined 



Table I. Day Length and Pupation: Xorth Carolina Midges 



Experiment 2 

 Result? after 40 Dav; Results after 60 Da>-5 



critical range were emploved. Experiment 1 used Maryland midges 

 collected Nlarch 5. 1954: the experiment started May 6. 1954. and 

 continued for 78 davs. Results, siven after 40 and 78 davs. show the 

 entire critical range to lie bet\seen a 12-hr photoperiod. which gave 



