INSECTS AFFECTING CITRUS FRUITS 453 



in its control. Sometimes as high as 80 per cent, of the scales 

 will show the small hole whence the adult parasite has escaped 

 from its .host. Yet the numbers of living scales that are left are 

 great enough often to make it necessary to use some artificial 

 methods of control. Most growers rely on fumigation to con- 

 trol this pest, but in some cases, especially in the case of young 

 trees, it is practical to spray. The kerosene sprays discussed 

 on page 416, have been found most satisfactory. 



FIG. 213. Black scale, 

 Saissctia olcts, on orange 

 twig. (Slightly en- 

 larged.) 



FIG. 214. Young of black scale, 

 Saissctia olea;. (About seventy times 

 natural size; after Quayle, photo by 

 Doane.) 



The hemispherical scale, ,5*. hemisphcerica, looks very much 

 like the black scale, but the dorsal surface is smooth and shining 

 and does not have the ridges that form the letter H. It is 

 often found on citrus trees out of doors, but is a more common 

 pest in greenhouses, where it attacks many kinds of plants. 

 The soft brown scale, Coccus hesperidum, is also sometimes 



