86 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 10 



The realization that in the ultimate control of the gipsy moth in 

 North America, the silvicultural aspect of the problem must receive 

 serious consideration is an indication of the importance of chemo- 

 tropism in the control of this pest. The elimination of favored food 

 plants and the substitution of unfavored species such as pine are meas- 

 ures largely based on the principle of food attraction, that is, of chemo- 

 tropism, and should be so regarded. 



Enticing and suggestive as the subject of chemotropism has been 

 shown to be, we must pass on to the next tropic reaction, namely, 

 thermotropism. In temperature we encounter an environmental 

 influence which is as far-reaching as it is universal in its relation to 

 insect behaviour, and while it is inseparably associated with other 

 factors, especially that of moisture which we shall consider later, it is 

 in itself sufficiently potent to determine the range of insect activity in 

 both time and space. The relation of temperature to the distribution 

 of insects is too well known to require demonstration by examples. 

 Merriam's laws of temperature control, namely: (1) that "animals and 

 plants are restricted in northward distribution by the total quantity 

 of heat during the season of growth and reproduction," and (2) that 

 "animals and plants are restricted in southward distribution by the 

 mean temperature of a brief period during the hottest part of the 

 year," in general, hold true in regard to insect distribution. The 

 importance of determining the optimum temperatures for the repro- 

 duction and development of different insects has been reaHzed by a 

 number of investigators, although their conclusions have sometimes 

 been defective through neglect to take into consideration the coopera- 

 tive effect of other environmental factors such as humidity. The 

 influence of temperature on development is illustrated very strikingly 

 in the Aphides. For example, Ewing has recently found that a con- 

 stant temperature of 90° F. is sufficient to prevent completely the 

 development of Aphis avence and that the optimum temperature for 

 the production of wingless agamic forms of this species is about 65° F., 

 these forms only being produced at a mean average daily temperature 

 of about 65° F. 



Practical use is now made of our knowledge of the temperature rela- 

 tions of insects in the employment of high temperatures as a means of 

 insect control, and "superheating" offers great possibilities. 



An interesting case of the use of temperature as a means of control 

 is afforded by the employment of the method of close-packing of horse- 

 manure for the purpose of preventing the breeding of Musca domestica. 

 About ten years ago I found that a temperature of about 105° F. was 

 fatal to the larvse of M. domestica and in an account given before this 

 Association in 1913 of further studies of the effects of the temperature 



