288 MOSQUITOES OF NORTH AMERICA 



these different kinds of water were not ordinarily very marked. They decided, 

 however, that the vigor and the strength and the size of the perfect insect which 

 resulted was in distinct relation with the larval food. Reed and Carroll found 

 that muddy water is unfavorable to the larvae. " In water, however, which con- 

 tains much suspended soil — muddy water — the larvae, in our experience, do not 

 flourish, but die off rather rapidly." 



DURATION OF EARLY STAGES. 



Temperature has the greatest influence, not only upon the hatching of the 

 eggs, but also upon the subsequent development of the larvae. The effects of 

 various temperatures on the early stages of calopus were carefully investigated 

 by the American commission in Cuba and by the French commission at Rio de 

 Janeiro and the results of both agree very closely. 



The shortest period of development to imago observed by Reed and Carroll 

 during summer weather in Cuba was 9^ days, divided as follows : incubation 2 

 days; larval stage 6 days; pupal stage 36 hours; but they believed that this was 

 quite exceptional. Their observations on the influence of temperature on de- 

 velopment are as follows : 



" We have just seen that at summer temperatures the time required for a com- 

 plete generation of this insect is from eleven to eighteen days. We may say that 

 at an average temperature of 75° F., or over, stegomyia multiplies abundantly. 

 Exposure to a cooler temperature, even for a short time daily, much retards the 

 development of this mosquito. Thus, a batch of fifty-one eggs kept at 35° C, 

 but which were placed in a cool chamber at 20° C. for two hours daily during the 

 whole process of development, although furnishing a few larvas at the end of the 

 third day, were not all hatched until the eleventh day. The first pupse appeared 

 on the fourteenth day and the first mosquito on the nineteenth day ; the whole 

 process being completed in twenty-seven days, instead of the usual fifteen or 

 eighteen days. The loss of insects was about 50 per cent. Eggs kept at a tem- 

 perature of 20° C. (68° F.) do not hatch, in our experience. Newly hatched 

 larvae kept at this temperature develop very slowly and require about twenty 

 days to reach the pupal stage. Mosquitos developed under such conditions are 

 feeble, and but few arrive at maturity. Young larvae kept at 10° C. (50° F.) 

 have failed to reach the pupal stage — although some growth takes place. In one 

 experiment more than 50 per cent, were dead at the end of two weeks, and none 

 survived the thirty-second day. Half grown larvae and pupse exposed to a tem- 

 perature of 20° C, and even as low as 10° C, continue to develop slowly, but the 

 few insects which escape drowning have, as a rule, been of feeble strength and 

 have refused to bite. Although the reduction of the temperature to the freezing 

 point, or below, would not necessarily destroy the vitality of the eggs of this 

 genus of mosquito, it should be remembered that a reduction of temperature to 

 68° F., or below, for even a few hours of the twenty-four, will much retard the 

 development of the generation. At a temperature less than 68° F. the eggs of 

 this insect have ceased to hatch." 



Under the most favorable conditions of food and temperature the larva de- 

 velops with great rapidity. When the conditions are very unfavorable larval 

 life may be prolonged indefinitely, the larvae showing great resistance. Agxa- 

 monte places the minimum period of development from egg to imago at ten 



