Greenhouse Insects 371 



gation with five ounces of cyanide to each 1,000 

 cubic feet of space for one hour will also be effective. 



Scale Insects 



There are various scale insects which attack green- 

 house plants. The black scale, Leeanium olea, at- 

 tacks the geranium and roses. Leeanium tessellatum 

 attacks palms. Aspidiatus nerii attacks a large and 

 varied number of house plants. 



Control, The safest method of treatment is fumi- 

 gation with hydrocyanic-acid gas. For directions, 

 see p. 385. 



White Fly (^Alleyrodes vaporaiorum West) 



The white fly is considered one of the worst 

 pests of some greenhouse crops. The plants most 

 affected are cucumber, lettuce, tomatoes, eggplants, 

 chrysanthemums, coleus, geraniums, and roses. The 

 pest injures the plants by attacking the underside of 

 the leaves and by sucking the tissue juices. The 

 insect deposits a sweetish, sticky substance which 

 tends to clog the stomata of the leaves, and frequent' 

 ly serves as the host for a sooty mold. 



Control. "White flies may be controlled by fumi- 

 gating with hydrocyanic-acid gas. For directions, 

 see p. 385. 



Plant Lice or Aphids (Apkidida) 



Plant lice (fig. 80, a) derive their food by suck- 

 ing the plant juice. In the greenhouse there seem 



