292 THE PRACTICAL APPLICATION OF ECOLOGY 



larval growth (autogeny) and fertilisation occurs in confined 

 spaces such as very small vessels (stenogamy). A number of 

 other workers have confirmed the existence of two such races, 

 but differing in various ways from the two French races just 

 referred to. The extensive literature on this subject is discussed 

 by Tate and Vincent (1936), and these authors have maintained 

 three autogenous strains of C. pipiens, and the general result of 

 their work confirms the conclusions of Roubaud and others that 

 there are two distinct races of C. pipiens in Europe. They point 

 out that confusion has arisen from the fact that Roubaud described 

 the autogenous race as an urban form, whereas it occurs in rural 

 areas also. It is true that it may breed freely in towns where 

 conditions are not suitable for the anautogenous race, but is not 

 confined to such habitats. The result of cross-mating experiments 

 show that interbreeding may take place in nature where the two 

 races co-exist. They find that the English autogenous race is not 

 subject to obligatory, cyclical hibernation. Prolonged illumination 

 has an activating influence on the females, both hibernating and 

 laboratory bred, and greatly stimulates gorging. With the aid of 

 artificial light during the winter months this race has been kept 

 breeding in the laboratory throughout the year for eleven genera- 

 tions without occurrence of cyclical hibernation. They think 

 that the reduced daylight may have an important influence in 

 inducing hibernation in autumn, since if given extra illumination 

 they remain active and feed. The females, whether they be of 

 hibernating or active generations, laid normally after one blood - 

 meal. Unfed females lived for a maximum of nineteen days and 

 never developed fat-body autotrophically. If fed on carbohydrate 

 food, in the form of fruit juice, for five weeks they accumulated 

 sufficient reserves to enable a small proportion of them to survive 

 fifteen weeks of subsequent starvation. Pairing always begins in 

 the air, but may be completed on the ground. The females do 

 not lay without a blood-meal and they show little tendency to 

 bite man, but attack birds voraciously. 



The strains of the autogenous race have been kept breeding 

 without blood-meals for several years and through forty-five to 

 forty-nine generations. This had no deleterious effects, a fact 



