CHAPTER XI 



INSECT BEHAVIOR 



The subject of insect behavior will be considered under three 

 heads: (i) Tropisms, (2) Instinct, (3) Intelligence. 



i. TROPISMS 



Environmental influences, such as light, temperature or 

 moisture, may control the direction of locomotion of an organ- 

 ism by determining the orientation of its body. The reaction 

 of the organism under these circumstances is known as a 

 tropic, or tactic, reaction. A moth, for example, flies toward 

 a flame is positively phototropic; a cockroach, on the con- 

 trary, avoids the light is negatively phototropic. A plant 

 turns toward the sun in other words, is positively helio- 

 tropic. 



An insect flies toward the light as inevitably and as mechan- 

 ically as a plant turns toward the sun ; indeed, the two phenom- 

 ena are fundamentally the same. Some students, however, 

 prefer to use the term taxis for bodily movements of motile 

 organisms, and the term tropism for turning movements of 

 fixed organisms. 



The study of tropic reactions, though comparatively new, 

 has already illuminated the whole subject of the behavior of 

 organisms and placed it on a rational basis. The complex 

 tropisms of insects offer a fresh and large field to the investi- 

 gator, comparatively little having as yet been published upon 

 the subject. 



Chemotropism. Positive and negative chemotropism, as 

 Wheeler observes, " are among the most potent factors in the 

 lives of insects." Insects are affected positively or negatively 

 by such substances as can affect their end-organs of smell or 

 taste. Positive chemotropism enables many insects to find 



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