1921 ENTOMOLOGICAL SOCIETY. 59 



effects of changing and nn usual conditions of heat and cold, snows and rains, 

 humidity and dryness, and other seasonal changes have long been known to be 

 important factors in regulating the number of insects. 



A variable winter is more fatal to most forms of insect life than a continuously 

 severe or a continuously mild winter. When insects go into hibernation they 

 become torpid and are able to resist quite low degrees of cold, but if thaws occur 

 they may become partially active for a short time. With every change of this 

 nature the insect loses vitality and this loss may prevent transformation in the 

 spring. Moreover, the effects of thaws in breaking up larval and pupal cells in 

 the ground are often quite marked. 



Sudden changes of temperature of say thirty degree range within a few 

 hours, which are quite common in our latitude, are very fatal to aphid® and many 

 caterpillars during their early stages. 



Another feature of the environment of insects is the different degree of 

 humidity demanded by each species or genus. Some insects like the thrips, chinch 

 bug, wheat midge and red spielers are more abundant under dr}< conditions, 

 while other insects like the plant lice and Hessian-fly develop best under moist 

 conditions. 



Observations seem to show that meteorological changes are often fatal to 

 those insects that live on the fringe of their distributional range. Under favor- 

 able conditions some insects may migrate northward, and even do much damage, 

 but such movements may be termed incursions, as they are temporary and 

 spasmodic in their character. 



The range of distribution of different insects has been mapped ,and this 

 has shown that insects tend to conform to the same zonal distribution as plants, 

 birds and mammals. Dr. Hopkins, of Washington, has extended our knowledge 

 of the Bioelimatic Law and has .shown how it may be utilized by the economic 

 entomologist in solving some of his problems. (See Article in 1919 Eeport of 

 this Society.) 



The recent study of tropisms appears to show that the movements and conduct 

 of insects are often the result of stimuli proceeding from the inorganic world, 

 such as light, gravitation, heat, electricity, moisture, pressure, and chemical sub- 

 stances. Already many interesting observations have been made and a few of these 

 have an economic bearing. 



It seems to me that this field of study, viz., the reactions of insects to stimuli, 

 is full of great possibilities for the economic entomologist. In the future, when 

 our knowledge of tropistic responses has greatly increased, we may expect to see 

 the introduction of many modifications of our present methods of control. 



He who studies attentively any common plant or animal may form a con- 

 ception, often an imperfect one, of the widely extending lines and cross lines 

 of inter-relationships with other plants and animals. The work of science is to 

 classify and describe these inter-relations, and in this line much progress has been 

 made since Darwin's day. The economic entomologist and botanist, who are 

 specially interested in the control of injurious insects and plants, must keep con- 

 stantly in view this idea of relationships in Nature if they would deal successfully 

 with the problems confronting them. 



At the recent meeting of the American Association of Economic Entomologists 

 at Philadelphia many prominent leaders emphasized the necessity for a more 



