602 PHOTOPERIODISM IN INVERTEBRATES 



prevented in adults of the mosquito Ciilex pipiens by exposure to 

 continuous light (Tate and Vincent, 1936). 



A general account of insect photoperiodism as related to diapause 

 was pubhshed recently by Lees (1955). Lees' timely review has been 

 especially helpful to the present authors since it summarizes important 

 papers in Japanese and Russian, translations of which were not 

 available to them. Additional investigations, apart from those related 

 specifically to diapause, have shown day length to be important in the 

 control of the seasonal pattern of wing production and reproductive 

 types in aphids (Marcovitch, 1923, 1924; Shull, 1928, 1929; Bonne- 

 maison, 1949, 1950; and others) and in the control of morphological 

 types in leaf hoppers (Bonnemaison and Missonnier, 1955; Miiller, 

 1954) and butterflies (Miiller, 1955). A summary of insect photo- 

 periodism shows that the phenomenon has been demonstrated in the 

 Odonata, Orthoptera, Homoptera, Lepidoptera, Diptera, Coleoptera, 

 and Hymenoptera (references given by Lees, 1955, and above). It 

 is becoming apparent that day length is a major environmental factor 

 in controlling seasonal activity in insects. 



MATERIALS AND METHODS 



The larvae of M. knabi develop in the water contained in the 

 leaves of Sarracenia purpurea and feed on the remains of small ani- 

 mals which fall into these pitchers. Pupation occurs just above the 

 surface of the water in a secreted gelatinous mass, and is completed 

 in about three days at 23 °C. Winter is passed in the larval stage; 

 mature larvae fail to pupate as winter approaches and do not resume 

 development until environmental conditions are again favorable. 

 Presumably several generations are passed during the summer without 

 interruption, and thus diapause is of the facultative type. Experiments 

 reported in this paper were conducted primarily to study the factors 

 controlling the termination of diapause. 



Larvae employed in experiments were collected from S. purpurea 

 growing either in Suitland Bog, Prince Georges County, Maryland, or 

 at various places in North Carolina. The specific sites of the latter are 

 named only when it seems relevant to the interpretation of the results. 



An attempt was made to use only fully grown diapausing larvae 



