296 GENERAL PLANT PATHOLOGY 



those with mandibulate, or bithig mouth parts, and those with hausti- 

 late, or sucking mouth parts. The first group includes the insects 

 that bore into wood, those that bite off the leaf surface (Fig. in) and 

 thus skeletonize leaves and those which tear or bite pieces out of leaves 

 and other plant parts (Fig. in). The sucking insects include those 

 like the bugs, aphids, or plant lice, and scale insects (Fig. 112), which 

 cannot be destroyed by stomach poisons. These latter insects by suck- 

 ing the plant juices do irreparable damage to all kinds of fruit and 

 shade trees, and reduce materially the yield of agricultural and 

 horticultural crops. 



Of the mites, the most destructive is the red spider Tetranychus 

 niytilaspidis. The red spider is probably identic with the insect 

 known throughout Florida as the Purple Mite. It is quite a small 

 insect, yet distinctly visible to the naked eye. They appear during 

 summer in great numbers and damage the oranges by causing the 

 fruit to drop and injure the foliage leaves so that they cannot perform 

 their functions properly. The leaves become spotted and lose their 

 glossy green color. The males and females are protected by stiff hairs 

 and their color is purplish, or reddish-purple in the old insects, but of a 

 lighter red when young. 



Animal galls are of various kinds. Those due to insects are charac- 

 teristic and will be described, when the pathologic anatomy of plants 

 is considered in detail. 



The field of Economic Entomology is a special one and there are 

 bulky treatises dealing with various phases of it. A useful book, and 

 written in an easy style is one by John B. Smith, late Entomologist of 

 the New Jersey Agricultural Experiment Station, and is entitled 

 "Economic Entomology for the Farmer and Fruit Grower." etc. 

 Although published in 1896, it is still a useful book. A few American 

 classics on the subject may be mentioned, as follows: 



Crosby, C. R. and Slingerland, M. V.: Manual of Fruit Insects, 



1915- 



Forbes, S. A.: Several Reports of the State Entomologist on the 

 Noxious and Beneficial Insects of the State of Illinois. 



Harris, T. W.: Insects Injurious to Vegetation (several editions). 



Insect Life, seven volumes (a mine of information on American 

 economic entomology). 



Packard, Alpheus S.: Insects Injurious to Forest and Shade 



