THE CANADIAN ENTOMOLOGIST. 85 



SOME TROPIC REACTIONS OF MEGILLA MACULATA 



DE G. AND NOTES ON THE HYDROTROPISM OF 



CERTAIN MOSQUITOES. 



BY HARRY B. WEISS, NEW BRUNSWICK, N, J. 



This ladybird, which is the only species in New Jersey hiber- 

 nating in sufficient numbers to be considered a colony, lends it- 

 self readily to experimentation, and the colonies containing as a 

 rule about a thousand individuals may be found in different local- 

 ities usually under a piece of bark or a mass of dried leaves. 



This colonial hibernation is the result of various reactions 

 to tropic stimuli. First the question arises as to just why they 

 congregate in large numbers and this may be explained by chemo- 

 tropism. All Coccinellidse emit peculiar odors and as the colony 

 increases, so does the odor, thereby making the chemotropic 

 stimuli stronger and more effective. Mr. Edward K. Carnes in 

 bulletin No, 5, Vol, I, of the California State Commission of Horti- 

 culture, writes that he has located colonies of Hippodamia con- 

 vergens in that state simply by the odor alone. Here, however, the 

 individuals in a colony number two and a half millions or more, 



A lowering of the temperature as winter approaches with a 

 corresponding decrease in the food supply undoubtedl}' renders 

 them exceedingly susceptible to chemotropic stimuli. With 

 Megilla maciilata, there is no evidence at present that anemotrop- 

 ism plays any part in the selection of the hibernating quarter. 

 Once in their place of hibernation, they become positively thig- 

 motropic and negatively phototropic. Two hundred individuals 

 were removed from a colony and placed in a glass breeding cage, 

 one end of which was constructed so that they could if they de- 

 sired act positively photo- and thigmotropic and the other end so 

 that they could act only negatively phototropic and positively 

 thigmotropic. Every one selected the dark end. This happened 

 on both sunshiny and cloudy days, During all operations the 

 temperature of the entire cage was uniform as indicated by thermo- 

 metric. tests. During the above experiment the temperature was 

 gradually lowered in eight hours from 70° F. to 36° F. 



At a temperature of 54° F. they remained as before, At a 

 temperature of 64° F. about one third became positively photo- 

 tropic and negatively geotropic, and their activity undoubtedly 



March, 1913 



