INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



41 



pastures and even in cultivated areas. The hopper-dozer is con- 

 structed as shown in Figs. 34, 35. The back and sides are made of 

 thin sheet iron or cloth and the pan at the bottom is constructed to 

 hold about two inches of water and kerosene or crude oil. These 

 hopper-dozers may be made any length but one easily drawn by 

 two horses is the most practicable. They are simply drawn across 

 the fields as a sled and capture the grasshoppers as they endeavor 

 to escape the apparatus. Though the insects may escape from the 

 kerosene or oil bath they are nevertheless doomed. 



The best time of operation is on warm days early in the season 

 before the grasshoppers have acquired wings. 



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Cross Section of Grasshobher Machine 



Fig. 36. — A grasshopper machine constructed without an oil pan for use in hilly 

 or rolling districts. (Wyo. Agrcl. Exp. Sta.) 



Natural Enemies.— There are many natural enemies of grasshop- 

 pers, which play a very important part in their control. In this work 

 only the most common ones will be mentioned. 



Parasitic Enemies. — The eggs of these parasites are usually laid 

 on the surface of the living grasshoppers. Upon hatching the larvas 

 make their way into the body and feed upon the internal organs, even- 

 tually killing the host. The tachina flies, bombylid flies, flesh flies 

 (Sarcopliaga sp.) and some other dipterous insects are notably destrue- 



