THE APHIS VASTATOR ON OTHER PLANTS. 87 



not appeared till August. Supposing, however, that from 

 their excessive numbers it should come before the grain is 

 formed, there is no doubt that the creature might annihilate 

 our crop. 



(352.) I do not believe that this creature can live upon 

 the oat. I have frequently examined oat plants in the 

 midst of dying potatoes, where the remnant of the troop of 

 the destroying Aphides were glad to find any domicile, but 

 I have not observed a single plant infected. The oat is, 

 however, assailed by a totally different Aphis, which is 

 quite as partial and destructive to it as the vastator is to 

 the potatoe. 



(353.) I have placed the two species together upon an 

 oat plant which was living in my sitting-room. In a few 

 days the vastator had entirely disappeared, whilst the other 

 species throve remarkably well, and is now existing in all 

 its stages of development, feeding on the stalks of the 

 young grain. 



(354.) Upon the wild barley grass, however, I have 

 found the vastator in great abundance, feeding and appa- 

 rently thriving well upon the leaves, which very soon die, 

 turn yellow, and decay under its destructive influence. 

 This grass is also preyed upon by another Aphis. 



(355.) A seedling pasture grass is liable to be attacked 

 by the vastator, which kills leaf after leaf, till, in some 

 cases which I have seen, the whole plant is totally destroy- 

 ed by it. In this case the vastator is generally conjoined 

 with another species, which is hairy and has no abdominal 

 tubercles. 



(356.) I am not aware that the vastator ever lives upon 

 rye, buck-wheat, peas, or beans. The Aphis which attacks 



