272 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 4 



I shall mention here some other troubles for want of knowledge to 

 properly classify them anywhere: The darker green color, swelling 

 at point of attack, and tendency to stool in wheat attacked by Hessian 

 fly; the swelling and russeting of apples following the work of curculio;. 

 the suck fly injury to tobacco, which impairs its burning quality; 

 leaf curl, due to leaf hoppers and thrips; stigmonose; red spots, due 

 to San Jose scale, etc. 



II. Diseases Indirectly Due to Insects 



A large number of bacteria and fungi which induce disease in plants 

 can enter the plant only through breaks in the protecting epidermis or 

 bark. The large majority of such diseases enter through insect 

 injuries, in many cases the insects actually carrying the infection on 

 their mouth-parts. 



Lindau, in volume two of the third edition of Sorauer's Pflanzen- 

 krankheiten, gives references to the following diseases introduced by 

 insects and other invertebrates: 



Vuillemin beheves the bacillus of the knot disease of Pinus hale- 

 pensis to be introduced by insects. 



The bacterial rot of hyacinths, etc., studied by Erwin Smith and 

 Wakker, may be introduced through wounds made by insects. 



It may be that some of the scab of potato is caused by Euchutrmds 

 {Oligochce'.ce) eating the surface of the tuber and the scab fungus after- 

 wards occupying the injured surface. 



Erwin Smith infected crucifiers with black rot by allowing Agri- 

 olimax agrestis to feed on leaves after being placed on pure cultures 

 of the Pseudomonas. The larva of the cabbage butterfly is probably 

 one of the chief means of introducing the bacteria in the field. 



Waite has shown that the bacillus of pear blight is carried to the 

 stigma, where the great majority of cases originate, from infected 

 sap escaping from the bark in spring. The cases of bhght on flower- 

 less twigs may be introduced through insect punctures in the young 

 bark. 



Vuillemin thinks that the olive knot bacillus enters through the 

 work of Phytoptus fraxini on ash trees. 



The bacillus of potato rot is thought to be introduced by insects. 

 Erwin Smith infected plants with Bacillus solanacearum by means 

 of the Colorado beetle. 



Earle considered the bacteria of point-rot of tomato to be intro- 

 duced through small insect punctures and insecticides a better means 

 of controlling the disease than fungicides. 



Erwin Smith infected cucurbits with Bacillus tracheiphilus, the 

 cause of wilt disease, by means of Diabroiica vittata and Anasa tristis 



