614 



PHOTOPERIODISM IN INVERTEBRATES 



Table VI. Dark-Period Interruption 



Group 



A 

 B 

 C 



D 



Control 



A 

 B 

 C 



Control 



Light Regime" 



No. Pupations of 

 Total Survivors 



Experiment 11 



Results after 49 Days 

 131 L, 10* D 20 of 27 



12 L, 2 D, li L, 81 D 27 of 28 



12 L, 5i D, 1 i L, 5 D 18 of 29 



12 L, 9 D, n L, U D 26 of 30 



IIL, 13D Oof 30 



Experiment 12 

 Results after 65 Days 



10*^ L, 2\ D, U L, 9f D 15 of 17 



lO^L, 6D, UL, 6D 9 of 15 



10^ L, 9f D, n L, 2\ D 19 of 19 



IIL, 13D Oof 19 



Percent Pupation 



74 

 96 

 62 



87 

 



88 



60 



100 







° L, hours of light; D, hours of dark. 



Table VI gives the light regimes used and the results obtained. It will 

 be seen that interrupting the dark period produced pupation even 

 though the total amount of light was without effect when given as a 

 continuous short day. (See Discussion.) 



Continuous Darkness (Experiment 13) 



Several workers have demonstrated that photoperiodic arthropods 

 respond to very short day lengths and continuous darkness in more or 

 less the same way that they respond to long photoperiod and continu- 

 ous light. Experiment 13 was designed to test this phenomenon in 

 Metriocnemus knabi. A group of 20 individuals was held in complete 

 darkness for 43 days, interrupted twice weekly for 1 or 2 min while 

 the larvae were fed and checked. A control group of 10 individuals 

 was maintained on an 11 -hr day. The experiment commenced Feb- 

 ruary 22, 1956, utilizing larvae collected in North Carolina on 

 December 26, 1955. At the end of the experiment 11 of 19 surviving 

 larvae in continuous darkness had pupated, whereas none of the 10 

 on an 1 1-hr day had done so. In this response to continuous darkness, 

 M. knabi is similar to most other arthropods in which it has been 

 tested. 



