REPORT OF THE SOCIETY 61 



The same writers described a typical lesion in thevascular bundles of infected 

 plants and isolated an organism agreeing in characteristics with Bacillus dianthi 

 Bolley. They, however, failed to re-infect with this organism. Later^ they 

 confirmed the presence of the bacillus,but found that it was present in cases where 

 the typical curly-leaf symptoms did not occur. They also showed that insects 

 from certain wild plants would not produce the disease until they had fed on- 

 infected plants, and this was soon after confirmed by Bonquet and Hartung^ by 

 means of more extensive experiments. The insects used in these t\vo investigations 

 were obtained from A triplex, Chenopodium and Artemisia. 



Bonquet and StahF later found that the round-leaf mallow {Malva rotiin- 

 difolia) might also serve as a host for the causal organism of the curly-top disease 

 and that the leaf-hopper is able to transfer the disease from the mallow to the 

 beet, or vice versa. 



Perhaps the most interesting fact disclosed by the investigations of Smith 

 and Bonquet* is the necessity of an incubation period in the bod}' of the insects 

 before they can transmit the disease. "The insect is not immediately pathogenic 

 after the act of feeding, but a period of at least twenty-four hours, but certainly 

 not much more than this, must elapse before it can produce the disease." — This 

 evidence clearly indicates that the insect is not merely a mechanical inoculator, 

 but may serve as a true host of the curly- top organism. 



Insects as Passive Carriers 



a. Direct Inoculators 



Sucking Insects an important agent in the spread of fireblight. The 



evident connection betw'een the prevalence of certain insects and the spread of 

 fireblight in orchards has long been recognised. Jones*, of the Ontario Agricul- 

 tural college, was the first to definitely prove the instrumentality of aphids in 

 spreading the disease. Stewart^ showed that a pure culture of the causal organism 

 {Bacillus amylovorus) , smeared on the uninjured leaves of young pear plants, did 

 not produce the disease except in the case of those plants on which he placed the 



■• Smith R. E. and Bonquet, A. New light on curK top of the sugar beet. Phytopathology', 

 V, pp. 103-107, 1905. 



^ Smith and Bonquet; Connection of a Bacterial organism with curly leaf of the sugar beet. 

 Phytopath. V, pp. 335-342, 1915. 



^ Bonquet, P. A. and Hartung, W. J. The comparative effect upon sugar beets of Eutettix 

 tenella from wild plants and from curly top beets. Phytopathology- V, pp. 2>A:S, 349, 1916. 



^ Bonquet and Stahl. Wild vegetation as a source of curly top infection of sugar beets. 

 Journ. Econ. Ent. X, pp. 392-397. 1917. 



^ Jones, D. H . Bacterial Blight of apple, pear and quince trees. Ont. Agr. Col. Bui. 1 76. 1909. 



^ Stewart, V.B. The Fireblight disease in nursery stock. Cornell, Agr. E.xpt.Sta. Bui. 329. 1913. 



