REPORT OF THE SOCIETY 63 



"they feed readily, and sometimes the writer has thought preferably, on wilted 

 leaves which are swarming with this organism. In this way their mouthparts 

 cannot fail to become contaminated and to serve as carriers of the sticky infection. 

 No other means of dissemination is known to the writer, and this is believed to be 

 the common way in which disease is distributed." Rand and Enlows^* confirmed 

 Smith's observations, and showed that Diabrolica 12-punctata is also implicated in 

 the spread of the disease. 



Smith has shown also that the black rot of crucifers is disseminated by the 

 larva of Plusia and the slug Agriolimax, and that the brown rot of Solanaceae is 

 spread by the potato beetle (Leptinotarsa 10-lineata). 



b. Indirect Inociilators 



Many insects may spread disease without introducing the germs directly into 

 the tissues of the plant. Successful infection depends on the presence of wounds or 

 on the ability of the pathogen to enter through stomata or water-pores, or to 

 pierce the epidermis. A good example of this method of transmission is afforded 

 by the spread of blossom blight (fireblight) by bees and flies, Waite, in 1891, 

 found the bacillus in abundance in the nectaries of apple blossoms and also on the 

 legs and mouthparts of bees, and thus established the agency of bees in the spread 

 of this form of fireblight. His observations, by the way, were the first exact 

 observations made on insect transmission of plant diseases. They have since 

 been confirmed by many workers. 



Infection through Insect Wounds 



Many spores freely scattered by the wind or other agency are unable to enter 

 the tissues of plants except through wounds. It is evident, then, that the num- 

 erous wounds made by insects — feeding punctures, tunnels, egg-laying punctures 

 — greatly increase the chances of infection, and it has been shown again and 

 again that disease very frequently enters through such channels. Stewart and 

 Eustace^^ pointed out that infection of raspberry canes with the cane-blight 

 (Leptosphaeria coniothyriiim) often takes place through the egg punctures of the 

 striped tree cricket {Oecanthus nigricornis). The writer has also on many 

 occasions made the same observation. 



Parrott and Fulton^' showed that in the apple the punctures of the allied 

 snowy tree-cricket {Oe. niveus) serve as points of infection for the same disease. 



^* Rand, F. V. and Enlows, E. M. A. Transmission and control of Bacterial wilt of cucurbits. 

 Journ. Agr. Res. VI, pp. 417-434. 



'5 Stewart, F. C. and Eustace, H. J., N. Y. Agr. Expt. Sta. Bui. 328. 1910. 

 i« Parrott, P. J. and Fulton, B. B. N. Y. Agr. Expt. Sta. Bui. 388. 1914. 



