139 



The third group consisting of the two mainspecies C. pipiens and T. annalata is 

 again of quite another type; here it is the impregnated female which hibernates; the 

 life of the imago with regard to the female lasting about seven months; the male hiber- 

 nates only in the spermatozoan stage. In spring the female lays her eggs, and these are 

 always laid in egg-rafts. Culex pipiens is the only Danish, and probably the only 

 North European species in which we have with certainty regularly observed a 

 series of generations in the course of the summer. Further south the same is the 

 case with T. annalata. Eyseix (1907 p. 198) says correctly: "Nur die im Imagosta- 

 dium iiherwinternden Stechmucken vermogen mehrere Generationen in einem Jahre 

 zu erreichen". As far as we know the two species in our country only rarely attack 

 man; C. pipiens probably mainly attacks poultry; T. annalata is best known as flow- 

 er visitor but also sucks blood from cattle. 



With regard to the impregnated females hibernating in the imago stage it may 

 be added that parthenogenesis in the mosquitoes, at all events as a rule, is highly 

 improbable (Kellog 1904 p. 59; Luhe 1903 p. 372). 



It has often been said when the attacks of mosquitoes in the warmest sum- 

 mer time have been extremely fierce that this is due to the large amount of gene- 

 rations and broods which follow each other with incredible celerity. This supposi- 

 tion which has especially taken root among common people, but has really been 

 nourished by the scientists, is quite wrong. The huge masses of mosquitoes are 

 not due to new generations; almost all our mosquitoes except C. pipiens and the 

 brackish water mosquitoes have practically only one single generation a year; if a 

 second generation appears, this is against the rule, and the number of individuals 

 is much smaller than in the first. The huge mosquito masses in the summer months 

 are principally due to the fact that the different species, which are hatched after 

 each other, keep on adding to the amount, and for a short time of the year all 

 bite simultaneously; when this has not hitherto been understood, it is also because 

 we have in a very high degree underrated the longevity of the mosquitoes; as men- 

 tioned above it may, more especially in damp, cold summers when the lust of 

 blood is feeble, be prolonged to about three months. One would be inclined to 

 think that exactly in the rainy summers, when the ponds are filled with water, the 

 best conditions would be found for production of new generations and augmenta- 

 tion of the mosquito plague. This supposition seems however to be quite wrong as 

 regards our country. In 1918 we had a very dry summer, in which all the ponds 

 from the latterjpart of May till the latter part of October were dry; many ponds 

 were not filled with water before next spring. In 1919 many ponds were laid dry 

 in the latter part of May but got water again in July; then most of them were 

 dry again in Aug. — September and got no water before December. As mentioned 

 before after the complete desiccation in June 1919 we really found larva 1 of 0. commu- 

 nis and 0. lutescens in July, but the number which was hatched was extremely 

 small, and there is no doubt that the mosquito plague was greater in 1918 than 



18* 



