AEDES CALOPUS AND TEMPERATURE 271 



days and that even when allowed to suck blood they will still die in a few days 

 if deprived of water. 



INFLUENCE OF TEMPERATURE. 



The French investigators pointed out that one of the most striking character- 

 istics of calopus is its extreme sensibility to differences in temperature and this 

 has been confirmed by many observations. They were impressed by the great 

 activity which the insect showed when the thermometer ranged in the vicinity 

 of 28° Centigrade (82° Fahrenheit), the temperature at which it displayed the 

 greatest energy. In contrast with this was the markedly reduced activity when 

 the temperature rose or fell a few degrees above or below that point. Beyond 

 39° C. (102° F.) the heat is fatal to it. If the thermometer goes below 15° or 

 16° C. (59° or 61° F.) it becomes sluggish and will not feed. At 12° to 14° C. 

 (54° to 57° F.) it becomes torpid, flies with difficulty and no longer stands 

 firmly on its legs. At temperatures of from 14° to 18° C. (57° to 64° F.) 

 calopus not only does not bite in freedom but refuses to bite when put in a glass* 

 tube and placed in contact with the skin. Only when the temperature inside the 

 tube is raised sufficiently by the heat of the hand does the mosquito bite. At a 

 temperature of 14° C. twelve mosquitoes in tubes were placed in contact with 

 the arm and kept there for 15 minutes without showing any willingness to bite. 

 At 17° C. the result was the same. At 18° C. nine of these same mosquitoes bit, 

 one after five minutes, the remainder after seven and eight minutes. These in- 

 vestigators do not believe that in nature calopus will bite below 17° C. ; they 

 found that it would bite readily between 22° and 25° C. (72° and 77° F.) but 

 that the temperature which suits it best is between 27° and 30° C. (81°-86° 

 F.) . Reed and Carroll made some interesting observations on the effect of tem-. 

 perature on biting with the yellow-fever mosquito. They may be quoted as 

 follows : 



" As regards the effect of temperature on the stinging of stegomyia fasdata, 

 the results of a number of observations made by us show that this mosquito will 

 bite at temperatures of 62° F. and above. At temperatures below this point, we 

 have not, as yet, succeeded in inducing even very hungry females to suck blood. 

 We may, therefore, say that observations thus far made appear to show that 

 stegomyia fasdata, while not breeding at temperatures below 68° F., will still 

 bite at a temperature as low as 62° F., but probably not at lower temperatures. 



" If this insect is concerned in the propagation of yellow fever, it is now quite 

 apparent why an epidemic of this disease should fall to a low ebb in the city of 

 New Orleans during the month of November, with a mean temperature of 

 61.8° F., and practically cease in December, with a mean temperature of 55.3° 

 F. A careful study of the charts herewith submitted, showing the monthly mean 

 temperatures of the cities of Havana and New Orleans and Havana and Rio de 

 Janeiro, together with the relative monthly mortality from yellow fever in these 

 cities, will prove of interest, we think, as showing better than laboratory ob- 

 servations the general effect of temperature upon the breeding and biting of 

 stegomyia fasdata. In the light of recent researches, we can now understand 

 that while yellow fever can, and does, prevail during the entire year in Havana 

 and Rio de Janeiro — although at a comparatively low ebb during the winter 

 months — it cannot propagate itself in New Orleans from December to May." 



