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TEXTBOOK OF ZOOLOGY 



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Many of the Hymenoptera live as parasites and are of great value 

 in biological control work. The braconids, ichneumon flies, and chal- 

 cid flies are examples of this group of parasites. A number of the 

 Hymenoptera are not beneficial, since they feed upon the leaves of 



Fig 197. — Above, adult female Simulium vittatum Zett. (From Knowlton. 

 Rowe and Madsen, by permission of the Utah Agricultural Experiment Station.) 

 Below, female big-headed fly, Pipunculus subvirescens Loew. (From Knowlton, 

 courtesy of Utah Academy of Sciences, Arts, and Letters.) 



our garden, orchard, and forest vegetation. There are many species 

 that are gall makers, attacking a wide variety of plants. Many 

 species are highly developed as far as social organization is con- 

 cerned, thousands of individuals living in a single colony. The 



