133 



Chap. III. 



Contributions to the Biology of the Culicines. 



a. General Biological Remarks. 



It is only during the last years that we have got some information with regard 

 to the longevity of the mosquitoes in the different stages of life; hut the informa- 

 tion we have got is still hut slight, and most of the remarks with regard to all 

 relations between the different stages and the seasons of the year still contradict 

 each other. This is mainly due to the fact that the determination, more especially 

 of the European species, has been very deficient; further, sufficient attention has 

 not been paid to the fact that species with wide areas of distribution are by no 

 means obliged to live their lives in the same manner near the southern and nor- 

 thern limits of their area of distribution. 



In his admirable chapter in "Histoire des Insectes" relating to the life-history of 

 C. pipiens Reaumur pointed out that this mosquito laid, its eggs in egg-rafts, the 

 well-known egg-boats; the boats were laid upon the surface of stagnant waters. For 

 more than a century it has been regarded as a fact that this was also the case 

 with all other mosquitoes. This thesis was strengthened by some observations with 

 regard to T. annulata, the eggs of which were also laid in egg-rafts. 



In Europe it was especially Galli Valerio and his pupils who showed that 

 C. pipiens, with regard to the egg-laying process, could by no means be used as a 

 model for all other mosquitoes. The significance of the many papers of these 

 authors is weakened by the fact that the determination of the explored species 

 is very deficient; some of the communications are, as Eysell (1907 — 1909) has 

 pointed out, undoubtedly wrong. It has however been shown that some of the 

 Culicidce of Switzerland hibernate as larvae or are able to hibernate as such, more 

 especially below withered leaves "in den eingetrockneten und mit Schnee angefiill- 

 ten Pfutzen"; that larva? during the whole winter develop into pup;c at a tp. of 

 4 — 6° C; that eggs of Culicidce are able to endure desiccation etc. Some of the 

 statements are unquestionably correct, some disagree with those of other observers 

 and need corroboration. 



In 1909 Eysell showed that only those mosquitoes (C. pipiens and T. annu- 

 lata) which hibernated in the imago stage, laid their eggs in egg-rafts, the others 

 laid them singly. Later on Howard, Dyar and Knab 1912 pointed out that it is 

 only the genera Cnlex, Culiseta and Tcvniorhynehus, which form egg-boats in ac- 

 cordance with the type of C. pipiens and deposit the boats on the surface of stagnant 

 waters. In the vast group of Aedini the eggs are laid singly or in small batches and 

 hardly ever on the surface of the water, but on the moist mud of the ponds where 

 the imagines were hatched, and often upon wholly sun-dried ground, commonly 

 covered with withered vegetation. The above-named authors further showed that the 

 Aedini hibernate as eggs; the eggs rest until the following spring and are hatched 



