608 



PHOTOPERIODISM IN INVERTEBRATES 



Temperature (Experiments 5 and 6) 



Experiments were conducted to determine critical photoperiods at 

 high, intermediate, and low temperatures. In one such experiment 

 (Experiment 5) the temperatures employed were 30.6 ± 1°C, 25.6 

 ± 1°C, and 12.0 ± 0.5°C. Photoperiods were llVi, 12, llVi, 11%, 

 13, and 13Vi hr in duration. The experiment, started June 15, 1955, 

 employed Maryland midges collected April 7, 1955. Results after 

 40 days (Fig. 2) showed httle difference between the photoperiodic 



II 12 13 



DAY LENGTH 



(HOURS LIGHT / 24 HOURS) 



Fig. 2. Temperature, day length, and pupation. Results after 40 days. 

 (Experiment 5.) 



response of the midges at an intermediate temperature (25.6°C) and 

 those at a low temperature (12.0-C). No pupations, however, oc- 

 curred at the high temperature (30.6°C). 



In a similar experiment (Experiment 6) the low temperature was 

 dropped to 8.3 ± 1°C, the intermediate temperature was 23.5 ± 1°C 

 and the high temperature was 29.5 ± 1°C. Maryland midges, col- 

 lected on June 19, 1955, were employed; the experiment started 



