232 MOSQUITOES OF NORTH AMERICA 



NUMBER OF GENERATIONS. 



The general impression is that, in temperate regions, there are several genera- 

 tions of Anopheles during a season and that they continue to reproduce while 

 conditions are favorable. Kulagin, in Eussia, appears to have been the only one 

 who has investigated the question carefully and after observations through 

 several years he concluded that there is but a single generation annually, the 

 images issuing from pupae not laying eggs until the following year. It is well 

 known that the female Anopheles do not lay all their eggs at one time. Accord- 

 ing to Kulagin the egg-laying period is extended over the entire summer through 

 the fact that some of the Anopheles do not leave their hibernation quarters until 

 well into the summer. He points out that in the female Anopheles examined by 

 Koschewnikow late in July all showed a strongly developed fat supply and un- 

 developed ova and that the presence of the fat was a preparation for hibernation. 

 We have already mentioned that in this country Smith has found the hibernat- 

 ing Anopheles in similar condition. 



The observations made by Kulagin in 1906 are very convincing. In that 

 year there was a very early spring in the province of Moscow ; the temperature 

 rose very high in April and there were no cold days. As a result of these early 

 favorable conditions the hibernating mosquitoes left their shelters very promptly. 

 Oviposition followed with the same promptness. He found great numbers of 

 larvae about the middle of April and these developed rapidly. The imagos 

 issued from the pupae during the last half of May, within a very short period. 

 From the end of May on, throughout June and July no Anopheles larvae could 

 be found in spite of the most thorough search. Kulagin then points out that the 

 conclusion is inevitable that in that year the females which issued from pupas 

 about the middle of May were the ones to hibernate. 



Observations made by one of us (Knab) on the mating habits of Anopheles 

 piinctipennis are significant in this connection. This species has been observed 

 repeatedly, swarming in the manner described on another page, but in every 

 case observed this occurred well towards the end of the season. 



Further observations are necessary to determine if all the species of Anopheles 

 of the temperate regions agree in the number of generations. As to the tropical 

 species, practically nothing is known as to the number of generations. Quite 

 probably in certain regions, where there is an abundance of water throughout the 

 year, breeding is continuous. In parts of India, where there is a long, well- 

 marked dry season, the behavior of the Anopheles appears to be much as in colder 

 climates, only that in this case the dry time is the resting period. Stephens and 

 Christophers state that in India aestivating Anopheles, although they feed at 

 intervals, will not deposit eggs even if suitable deposits of water are present. 



GEOGRAPHIC DISTRIBUTION OF MALARIA. 



The distribution of malaria coincides in a way with the distribution of the 



mosquitoes of the genus Anopheles; that is to say malaria does not originate in 



localities where Anopheles does not exist; but on the other hand there exist 



many localities where there are Anopheles where malaria is not to be found. 



