25 * 



Moults. As far as we know hitherto, all mosquito larva? moult four times 

 and transform into pupa with the fourth moult; the moulting processes, the different 

 aspects of the larvae in the different larva stages, have been mentioned by different 

 authors. I more especially refer to the very valuable paper by Eysell (1911 p. 320), 

 to the remarks in Howard, Dyar and Knab (1912 p. 97), and to the most recent 

 investigations by Lang (1920). The ripe larva ready to pupate is always easily 

 recognisable, the body being more opaque; the compound eyes are dorsally drawn 

 out into a sharp point, and the trumpets appear as dark spots below the larva skin 

 and near the anterior angles of the thorax. 



Here I only wish to call attention to a few facts, hitherto as far as I know 

 overlooked. 



It has been mentioned that two of our Culicin larva?, Culicella morsitans and 

 Ochlerotatus rusticus, hibernate in the larva stage. These larva? are hatched in Sep- 

 tember or late autumn, but they have commonly passed the third moult before the 

 winter sets in. The wintering generally takes place in the last larva stage before 

 the pupation. In the long time from November — December to May — June when 

 C. morsitans pupates, the larva?, at all events in my aquaria, do not moult. The 

 same remarkable fact I have observed with regard to the Perlidce, Ephemeridce 

 and Zygopteridce, which are hatched, in autumn and are ready to leave the water 

 in spring. In the course of the autumn as the temperature sinks they hasten to 

 reach the last larva stage before winter sets in. It seems as if all these different 

 insects are under the same law, that hibernation can best take place in the last larva 

 stages. It is very remarkable that the first larva stages are often passed in the course 

 of a few days, whereas the last may take more than a half year. The larva 1 eat in 

 the last moult as well as in the earlier; in the first, the result of the nutriment is 

 growth and new moults, in the last there is no, or extremely little, growth. With 

 regard to Perlidce and Ephemeridce the phenomenon is intelligible, because the re- 

 productive organs ripen during the last months; in the last days before the nymphs 

 leave the water, the abdomen bulges with ripe eggs. In the Culicin larvae this is 

 however not the case; here the process is by no means carried so far, the repro- 

 ductive organs in the pupa too being only small; as far as we know the imagines 

 of the Culicida 1 regularly use a fortnight or more to ripen their eggs after meta- 

 morphosis. 



Further it is peculiar to see how all the larva 1 of the same species in a pond 

 keep time with each other with regard to the moults; they are hatched almost on the 

 same day and moult on the same day; in the course of a few days all larva 1 are 

 altered into pupa 1 and in one or two days all animals leave the pond as imagines. 

 When therefore in these spring-ponds with older larva 1 , new broods of larva 1 in the 

 first stage suddenly arrive, it has been ascertained, that these young very often belong 

 to another species, the hatching temperature of which is higher than that of the first 

 hatched. Only when heavy showers have raised the water line, and some eggs of 

 the first-arrived species, have thus been reached by the water, it happens thai 



D. K. D. Vldenak.Selsk, Skr., naturvidensk. og mathem. Afd. 8. Riekke, VII, 1. i 



