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 the* 

 circumstances is known as a tropic, or tactic, reaction. A moth, for ex- 

 ample, flies toward a flame is positively phototropic; a cockroach, 01 

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

 toward the sun in other words, is positively heliotropic. 



An insect flies toward the light as inevitably and as mechanically 

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

 mentally the same. Some students prefer, however, to use the tei 

 taxis for bodily movements of motile organisms, and the term tropisi 

 for turning movements of fixed organisms. 



The study of tropic reactions has already illuminated the entir( 

 subject of the behavior of organisms and placed it on a rational basis, 

 and the complex tropisms of insects offer a fresh and large field to th< 

 investigator. 



Chemotropism. Positive and negative chemotropism, as Wheele 

 observes, "are among the most potent factors in the lives of insects." 

 Insects are affected positively or negatively by such substances as 

 affect their end-organs of smell or taste. Positive chemotropij 

 enables many insects to find their food or their mates; and negative 

 chemotropism enables them to avoid injurious substances. This 

 negative reaction on the part of other organisms is made use of also b] 

 such insects as emit repellent odors. 



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

 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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