Part II.— LIFE STUDIES AND CONTROL OF INSECTS 



(Introduction to second-year work) 



LIFE STUDIES 



(How insects grow) 



Once the insect becomes an adult it never grows any larger. A 

 gnat will always be a gnat : it is not a baby fly. Insects make all their 

 growth while in the immature stages. There are, however, two types 

 of growth. Some insects, like the grasshopper, develop gradually, 



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Figure 103. — Incomplete metamorphosis. 



and each time they shed their skin, the newly emerged young more 

 closely resemble the adults. We call this incomplete metamorphosis. 

 Grasshoppers, crickets, the true bugs, and plant lice go through in- 

 complete metamorphosis. 



The young or larvae of the butterflies and beetles do not resemble 

 the adult. When the larva has completed its growth, it goes into a 



@ 



Figure 104. — Complete metamorphosis. 



pupal stage where the complete change, which we call complete 

 metamorphosis, takes place. Butterflies, beetles, wasps, and flies go 

 through complete metamorphosis. 



CONTROL OF INSECTS 



Many years ago very little was done about insect control, as out- 

 breaks that caused serious damage occurred only occasionally. Since 

 then many changes have taken place, and we have an entirely dif- 

 ferent problem today. 



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