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 organism 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 ex- 

 ample, flies toward a flame is positively phototropic; a cockroach, on 

 the contrary, avoids the light is negatively phototropic. A plant turns 

 toward the sun in other words, is positively heliotropic. 



An insect flies toward the light as inevitably and as mechanically as 

 a plant turns toward the sun; indeed, the two phenomena are funda- 

 mentally 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 al- 

 ready 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 investigator, 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 en- 

 ables many insects to find their food or their mates; and negative chemo- 

 tropism enables them to avoid injurious substances. This negative re- 

 action on the part of other organisms is made use of also by such insects 

 as emit repellent odors. 



A maggot orients its body with reference to a source of food and then 

 moves toward the food just as mechanically as a moth flies to a flame. 

 The maggot, as Loeb maintains, is influenced chemically by the radiat- 

 ing diffusion from a piece of meat, and follows a line of diffusion to the 



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