RELATION TO THE FARMER 257 



the plant bugs of the Capsid series have it very strongly 

 developed and Coreids like the common squash bugs 

 are well known for the poisonous effects of their punct- 

 ures on vines and other plants. 



Some plant lice form galls, sores or cankers on 

 branches, trunk or even the roots, like the woolly louse 

 of the apple; and some of these canker sores offer 

 excellent points of entrance for germs of disease and 

 decay. Indeed it has been charged against some of the 

 species that certain plant diseases are either carried or 



FIG. 118. Woolly apple-louse at c, showing galls made on roots at a, 

 the woolly wingless form at b. 



given points of entrance by them. The root-feeding 

 forms are particularly dangerous, because until the 

 tree or other plant begins to show bad condition there 

 is no way of recognizing their presence. 



Not all the injury done by these various forms of 

 sucking bugs is obvious, and so used does the farmer 

 become to the loss that very often he does not appre- 

 ciate it. A simple experiment made by one of our 

 economic entomologists proved that leaf-hoppers in 

 grass fields in his state were so numerous that they 

 shortened the crop one-half. Demonstration of this 

 was made by dividing a meadow into two equal parts, 

 pasturing cattle on both, but collecting the leaf-hoppers 



