290 MOSQUITOES OF NORTH AMERICA 



duced imagos. With mixtures up to 8 and 9 per cent the larvae developed nor- 

 mally but when the salinity was increased beyond this the larval period was 

 greatly prolonged. Under these conditions larvae lived for 50 days without 

 transforming. One larva, in a mixture with 10 per cent sea-water, died without 

 transforming after having lived 92 days. Larvae well advanced are much more 

 resistant and when nearly full grown would still transform in highly saline 

 water. In a proportion of 50 per cent sea-water the larvae generally survived 

 24 hours and those that were nearly full grown transformed to pupae. Beyond 

 this the larvae only transformed when they were within one or two hours of the 

 pupal stage and then only in mixtures up to 56 per cent sea- water. Of 50 larvae 

 placed in a mixture of 60 per cent sea-water three survived to the third day. 

 The pupae, when placed in pure sea-water, always produced imagos in a normal 

 manner. 



These experiments are of considerable economic importance, as they show that 

 the larvae of cdlopus may, in nature, survive in water which has, through evapo- 

 ration, reached a high degree of salinity. If afterwards, through rains, the solu- 

 tion becomes again diluted the larvae may then develop to imagos. 



Experiments were also made with solutions of pure salt (NaCl) and it was 

 found that the larvae would not withstand solutions stronger than one per cent. 

 Only once a larva transformed to pupa in a solution of 1.5 per cent, but in this 

 case the larva was already full grown and ready to moult. 



The Brazilian investigators also experimented with corrosive sublimate. In 

 the presence of 1/1000 the larva of calopus, on the average, died after one and 

 a half hours and the pupae but rarely produced imagos. With 1/2000 the larvae 

 died, on the average, after 4J hours and the pupse produced imagos. With 

 1/10000 a very few larvae developed to imagos, but this only happened when 

 they were in the last stage. 



At Rio de Janeiro it was found that the tanks used for washing clothes were 

 favorite breeding-places of Aedes calopus. Both the French commission and the 

 Brazilian investigators experimented on the effect of soap in the water on the 

 larvae. 



In their experiments with soap the French investigators found that larvae of 

 any age placed in a solution containing one-thousandth by weight Marseilles 

 soap died in five minutes. In solutions of one to five thousand and one to ten 

 thousand, they lived for a time but finally died. In solutions of one to two 

 hundred thousand and one to two hundred and fifty thousand, they developed 

 normally. The larvae bred normally in basins and tubs in which linen is cus- 

 tomarily washed, because, when the soapy water remains in the tubs for some 

 days, its alkalinity is greatly diminished. Peryassii experimented with common 

 Brazilian washing soap. He found that larvae of any age, when placed in a 

 solution of one-thousandth by weight died in from six to seven minutes. Only 

 when the solution was weakened to 1/200000 or less did the larvK develop in a 

 normal manner. 



In apparent contradiction to this extreme sensitiveness to alkalinity are the 

 observations of Agramonte, already mentioned, that the presence of wood ashes 



