282 MOSQUITOES OF NORTH AMERICA 



Cruz gives 10 to 24 hours as the duration of the egg-stage. Goeldi gives the 

 minimum duration as three days. The French commission indicate a minimum 

 period of two days. 



It appears that eggs which have been deposited out of the water hatch very 

 promptly when submerged, just as is the case with related species of Aedes. 

 When the eggs are deposited directly upon the water they require at least two 

 days to hatch. The discrepancies in the data of different observers can probably 

 be explained by these facts. 



Eggs deposited on the surface of the water float, but they are easily sunk by 

 disturbing the water. Goeldi states that eggs invariably perish when submerged. 

 The investigations of the French commission show that this is not the case. 

 They found that hatching is somewhat retarded by immersion and that some- 

 times some of the eggs do not hatch, particularly if the temperature of the water 

 is rather low. Peryassii found that if eggs were submerged a day after being 

 laid, and the temperature was not below 26° C. or above 29° C. (79°-84° F.), 

 they would hatch at the same time with those that floated. It would seem how- 

 ever that the eggs which are submerged soon after being laid generally perish. 



The French investigators found that the eggs suffered when immersed in water 

 at low temperature for a considerable time. They were not only subject to the 

 attacks of various organisms under these conditions but the egg-shell was also 

 gradually softened and would finally allow the water to enter. Eggs which have 

 perished by prolonged immersion do not remain intact but split open. While 

 in hatching the egg splits transversely at about one-fourth from the larger end, 

 the dead egg splits open longitudinally. The French investigators conclude that 

 survival of the eggs is much more certain in a dry state than when submerged. 



In Cuba, according to Eeed and Carroll, the eggs begin to hatch in summer 

 temperature, as a rule on the third day. They record two days as the shortest 

 egg period. Presumably these observations were made with eggs deposited 

 directly upon the water. 



The French commission found that a temperature of 27° to 29° C. (81°- 

 84° F.) was the most favorable and in it the eggs would hatch within two or 

 three days. At a temperature of 25° to 26° C. (77°-79° F.) the eggs usually 

 still hatched with considerable regularity after four or five days. At high tem- 

 peratures the eggs from one batch hatch together, or at the most within a few 

 hours of each other. Below 25° C. hatching is irregular and only part of the 

 eggs hatch, and below 20° C. (68° F.) it ceases altogether. In temperatures 

 between 25° to 20° C. but a few larvge appear and generally all the eggs remain 

 dormant until there is a rise of temperature. 



The eggs will survive Ioav temperatures down to the freezing point. While 

 ordinarily the chilling of the eggs is not fatal it nevertheless has a bad effect on 

 the entire development of the mosquito. In nature a drop of temperature to 

 below 20° C. in a single night will not only retard the hatching of the eggs but 

 also the development of the larvae. The French investigators further determined 

 that the eggs will withstand temperatures of from 20° C. to freezing for a con- 

 siderable time; if then subjected to a suitable temperature the eggs will hatch. 



