REACTIONS OF MOSQUITOES TO LIGHT 31 



phototactic response, as any orienting tendency which may be 

 present and which may perhaps account for the direction of 

 locomotion would naturally be obscured by the contortions of 

 the larvae during their progress through the water. Age makes 

 little difference in the reactions to light. Experiments tried with 

 larvae less than a day after hatching, elicited the same responses 

 as in older larvae although they were a little less decided. The 

 behavior of the pupae, up to even a short time before the emer- 

 gence of the imago, is practically the same as that of the larvae 

 both as regards reactions to shadows and positive phototaxis. 

 The reactions of the larvae and pupae of Culiseta inornatus, 

 Aedes fuscus and Aedes curriei are essentially the same as in 

 the species of Culex above described. 



Larvae exposed frequently to shadows gradually fail to respond 

 to them. A dish containing about thirty three-day old larvae 

 was shaded by passing an object over it once every minute, 

 the object being passed as nearly as possible in the same way 

 and with the same degree of speed. At the first trial all (about 

 twenty-five) which were at the surface went down. At the 

 second shading about fifteen went down, leaving nine at the 

 surface. In subsequent trials the number remaining at the 

 surface gradually decreased. From the tw^elfth to the sixteenth 

 trials none descended; in the seventeenth, six went down, after 

 which numerous subsequent trials produced no response. In 

 another lot all failed to respond after the seventh trial. Other 

 experiments yielded very similar results. One lot of larvae was 

 rather exceptional, however, in that they rapidly diminished in 

 responsiveness in the first three shadings, but up to the fifty- 

 fifth trial there was no further reduction in the number descending. 



The adult mosquitoes, like the larvae and pupae, show a 

 peculiar combination of reactions to light. It is well known 

 that they are much more apt to settle upon dark objects than 

 upon light ones, and that people wearing dark clothes are more 

 apt to attract them than those with light-colored apparel. Dur- 

 ing the day they seek the shade, even when it is not hot or dry, 

 and darkness brings them out of their haunts. Within doors, 

 while occasionally found on the windows and the light areas of 

 the room, they very frequently retreat into the shaded nooks. 

 But like most moths and many other forms which seek the 

 shade, they frequently show a decided positive phototaxis. 



