15 



conditions of temperature this stage lasts not less than 6 or 7 days; 

 under conditions where the supply of food is scanty or the tempera- 

 ture reduced the duration of this stage may become very much pro- 

 longed (weeks) or development may altogether cease. In the latter 

 case the larva may die without completing its metamorphosis or, with 

 the return of favorable conditions, it resumes its development. Freez- 

 ing for short periods does not appear to injure it. 



Pupa. — After several moults the larva changes into the pupa (fig. 8). 

 The pupa is not provided with a mouth and does not feed. It spends 

 its time at the surface of the water for, like the larva, it is an air 

 breather, and is provided with two trumpet-shaped breathing tubes 

 which spring, not from the tail as in the larva, but from the dorsum 

 of the thorax. It moves only when disturbed, and then rather rapidly 

 and jerkily downwards into the depths. The pupal stage lasts at least 

 36 hours, during which time important changes take place in its inter- 

 nal organization preparatory to the 

 emergence of the perfect insect or 

 imago. The pupal, like the larval 

 stage, is normally passed in the water. 

 Berry has shown, however, that the 

 pupa may be spilled on the ground 

 without its metamorphosis being in- 

 terfered with. Under the most favor- 

 able conditions it takes at least 9 

 days from the time the egg is laid to 

 the appearance of the imago. 



Lonaevitv. — The length of life of Fig. 8.-Pupa of Stegomyia calopus (after 

 , y . . ., , i Howard, 1901). 



the adult female under natural con- 

 ditions probably varies greatly. Experimentally, Guiteras (1904a) 

 succeeded in keeping a presumably infected one alive for 154 days at 

 the fall and winter temperatures of Habana. At summer tempera- 

 tures, deprived of water, it does not usually survive longer than 3£ to 

 4 days, and only very exceptionally 5 days. This fact has a bearing 

 on the possibility of transporting the mosquito in bandboxes or trunks. 

 Its activity, which is greatest at about 30° C. (86° F.), distinctly 

 diminishes as the temperature declines and approaches 20° C. (68° F.). 

 Below the latter point and as the temperature of 15° C. (59° F.) is 

 approximated the insect seeks obscure corners for protection, becomes 

 very sluggish, and can only exceptionally be induced to bite. In a 

 refrigerator at 8° to 10= C. (46.5° to 50° F.) Guiteras (1904a) was able 

 to keep some mosquitoes alive without food or water for 87 days. 

 How much longer they mave have lived it is impossible to say, because 

 the experiment was terminated at the end of this time by some ants 

 that gained access to and destroyed the mosquitoes. A freezing tem- 

 perature kills the mosquito rather quickly. 



