CHAPTER I 



INSECTS IN GENERAL 



Knowledge of the structure, development, classification and methods 

 of control of insects in general will enable the reader to understand better 

 the text dealing with any individual insect. The purpose of the brief 

 discussion in this chapter is to give that preliminary setting. 



STRUCTURE 



All adult insects have the head, thorax (chest) and abdomen more 

 or less distinctly separated. Attached to the front of the head are two 

 antennae, or feelers, as they are popularly called. The mouth parts are 

 formed for biting or sucking. Those of biting insects, such as grasshop- 

 pers, flea-beetles and alkali-beetles, consist of hard, sharp-edged jaws. 

 Sucking insects, such as the false chinch bug, plant-lice and others, have 

 the mouth parts prolonged into a long, straight beak which is often jointed. 

 In the case of moths and butterflies the larvae have biting mouth parts 

 while those of the adults are in the form of a slender proboscis, which is 

 carried coiled beneath the head. In the adult stage there are always 

 three pairs of legs attached to the thorax. These three pairs of legs are 

 present in the immature stages of beetles, the true bugs, moths and but- 

 terflies, while the young of the two-winged flies, bees, wasps and others 

 are legless. Aside from the true legs, which are located near the head, 

 caterpillars have from two to twelve fleshy leglike organs on the ab- 

 domen. These are called prolegs or props. These prolegs are furnished 

 with both hooks and suction pads. Most adult insects have one or two 

 pairs of wings, which are also attached to the chest. 



Insects breathe through small openings or spiracles in the abdomen. 

 From these openings the air is carried through tubes called tracheae, lead- 

 ing to the various parts of the body. 



Spiders, ticks and mites are not insects, but belong to a group of 

 invertebrate animals which have the head, thorax and abdomen closely 

 united and possess four pairs of legs in the adult stage; however, in the 

 immature stages some have but three pairs. 



DEVELOPMENT 



In the course of their development most insects undergo remarkable 

 changes in form. These changes constitute what is known as insect 

 metamorphosis. 



One order of insects develops without change in form or without 

 metamorphosis. The young when hatched from the egg have the same 

 form as the adult. A common representative of this group is often seen 

 floating in dense masses on water. Another is sometimes seen hopping 

 about on the snow during warm days in early spring in northern latitudes. 



The insects belonging to another class undergo considerable change 

 in form during their development, but the young resemble the adults 



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