616 PHOTOPERIODISM IN INVERTEBRATES 



ment during the diapause period in nature, since the intensity of direct 

 moonlight falls within the range 0.01-0.05 ft-c. An answer can be 

 seen, at least in part, from the fact that a relatively large number of 

 successive inductive cycles are required — 10 to 14 at 23 °C (Experi- 

 ments 8 and 9) — to induce development and that low temperature 

 (Experiments 5 and 6) slows the rate of response. It must be remem- 

 bered also that the light intensity reaching the larvae in nature is 

 reduced through shading, since the larvae live in the leaves of the 



pitcher plant. 



To make possible a correlation between these experimental results 

 and events in nature, collections, each consisting of many hundred 

 larvae, were made in the spring and fall to determine when pupations 

 begin and cease in midge populations in North Carolina. In the spring 

 of "l 95 5 collections were made near Spout Springs, Harnett County, 

 North Carolina (about 35° 15' N. Lat.). Larvae taken February 19 

 and returned to the laboratory, where they were placed on a 1 1 -hr 

 day, started pupating on February 28. A second collection made on 

 March 7 produced pupations the following day. It is concluded that 

 those larvae collected February 19 had been induced to pupate by 

 natural day lengths, which had just become long enough to be 

 inductive, but that the response was so newly set in progress that 

 several days were required in the laboratory before it was expressed. 

 Fall collections were made at two locations. On August 30, 1955, 

 larvae in Horse Cove, near Highlands, Macon County, North Carolina 

 (about 35° T N. Lat.) were pupating, as were larvae collected on 

 September 9 at Mulkey Gap, near Cashiers, Jackson County (also 

 about 35° 2' N. Lat., and approximately 6 1/2 miles from Horse Cove). 

 No pupations, however, occurred from a collection made at Mulkey 

 Gap on October 1. Diapause had been induced sometime between 

 September 9 and October 1. A winter collection made December 26, 

 1955, in Duncan Valley, near Cedar Mountain, Transylvania County 

 (about 35° 5' N. Lat.) yielded no pupations. No midsummer collec- 

 tions were made in North Carolina, but many pupations were observed 

 in pitcher plants at Suitland, Maryland, on June 19, 1955. 



The correlation between dates for initiation and termination of 

 diapause and natural photoperiods at 35° 0' N. Lat. is shown in Fig. 3. 

 Three day length curves are given, one for the period between sunrise 



