36 Psyche ]February 



POSITIVE THIGMOTROPISM OF CULEX PIPIENS IN 

 HIBERNATION. 



By Harry B. Weiss, 

 New Brunswick, N. J. 



Commencing about the middle of September, gravid females 

 of Culex pipiens become strongly negatively phototropic and seek 

 dark hibernation quarters which in the cities consist of cellars, 

 basements, closed empty houses and the like. They must how- 

 ever be dark. The activity of these hibernating individuals 

 depends entirely upon the temperature of the cellar or other place 

 selected. If the place be warm, they are quite active when dis- 

 turbed and if cold they are more or less torpid. Positive thigmo- 

 tropism is of course exhibited only by those hibernating in warm 

 places. 



After having become acclimated to these surroundings, the 

 negative phototropism seems to be entirely supplanted by positive 

 thigmotropism. Phototropic stimuli no longer produce responses. 

 Upon being disturbed, they fly readily, but not far from their 

 place of rest which is usually the lower side of a wall and always- 

 return to a similar position. 



A shaft of sunlight manipulated by mirrors and thrown upon 

 specimens in these positions produced absolutely no reactions. 

 A sixteen candle-power electric light placed a foot away from speci- 

 mens and allowed to remain there for an hour, also produced no 

 response. The insects made no attempt to fly into a region of less 

 illumination or from a less to a greater, but remained clinging to 

 the wall. Of course it must be remembered that they were in a 

 slightly dormant condition. Nevertheless they responded actively 

 to mechanical stimuli. 



In addition to being positively thigmotropic, gravid hibernating 

 females of Culex pipiens are negatively geotropic. They always 

 assume a position with the long axis of the body perpendicular to 

 the earth and the head pointing upward. Never have I seen one 

 in a different attitude. 



The tropisms of C. pipiens are varied and interesting. Taking 

 the female, we find her during the summer to be normally nega- 



