RELATION TO THE FARMER 



255 



a destructive increase under cultural conditions is almost 

 inevitable. 



Now in what ways do insects injure the crops 

 and cause injury to the agriculturist? This might 

 be answered by a reference to Chapter III, but it 

 may be useful to take up some features more in detail, 

 with the injury rather than the insects as the prime 

 objects of consideration. 



Plant lice do their mis- 

 chief in part by directly 

 exhausting the plant of 

 sap, partly by causing dis- 

 tortions of growth, and 

 partly by preventing the 

 proper maturing of the 

 fruit, be it on shrub, tree 

 or vine. If on the roots, 

 the plants are weakened 

 or often killed and even 

 trees are sometimes seri- 

 ously injured. A secondary 

 cause of injury is due to 



the production of honey-dew by the lice. This serves as 

 a culture medium for a black soot fungus which often 

 disfigures tree fruit to such an extent as to make it un- 

 salable. Some of the scales have a similar habit and so 

 do some Psyllids and Membracids. The enormous re- 

 productive powers of plant lice render them especially 

 dangerous, and very often the farmer does not even 

 see the nucleus from which come the hordes that he 

 finds on his wheat, his cabbages or his melons, a few 

 days later. 



During a spell of dry weather it may be noticed 

 that the oats or the grass is showing white spots or 

 becoming silver-tipped; or the onions begin to show 



Thrips, with antenna and 

 tarsus. 



