270 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



by mycologists, led away from the disease itself to the more thorough 

 study of the causative organisms. 



I wish to consider in the following paper the effect of insects upon 

 the plant rather from the standpoint of plant health, than from the 

 standpoint of the insect or of the entomologist, and in my judgment 

 this would be the true attitude of the economic entomologist who 

 wished to build his science upon the firmest foundation. 



The action of insects upon plants may (1) directly impair the health 

 of the plants, and may be considered under the head of (1) simple 

 injuries, and (2) definite diseases which follow as a result of insect 

 injuries or the presence of insects or their products in the plant tissues; 

 or their action inay be (2) indirect in that they actually introduce fungi 

 or bacteria which cause disease, or these organisms may enter 

 through the openings in the epidermis made by insects. 



I. Direct Injuries 



The chief effect of insects is the actual destruction of plant parts 

 in the process of feeding, nest building or oviposition. While the loss 

 of many organs is not so serious as with animals, owing to the great 

 number of structures having the same function in most plants, growth 

 and production is greatly reduced by the enormous losses on the 

 whole, as, for example, in the reduction of carbon assimilating sur- 

 face when such insects as army worms and other caterpillars, potato 

 bugs, grasshoppers, etc., feed upon the foliage. Reproduction is 

 interfered with through seed destruction by such insects as grain weevils, 

 Angumois grain moth, wire worm, wheat midge; the embryo may be 

 actually destroyed or the stored food removed so its growth is impaired. 

 Reproduction is also interfered with at an earlier stage by insects such 

 as the corn worm when feeding upon the silks and pollen. While 

 codling moth and cotton boll-weevil interfere some with the repro- 

 ductive organs, they are chiefly feared for the havoc they work to 

 ' products of more use to man than to the plant. 



Another form of injury is where the material for growth is removed 

 by insects which suck out the plant juices, and while more serious 

 trouble may occur at the point of attack the chief loss is in building 

 material. The removal of material from the wood of stem or root 

 may interfere with the mechanical stability of the plant and it breaks 

 or is uprooted. 



Physiological Troubles Following Injury 



When plant roots or the woody stems have been destroyed by 

 insects, wilting may follow from inability to secure water (e. g., squash 

 bug, bean vine borer, striped cucumber beetle) or if the damage is not 



