628 Journal of Agricultural Research voi. x. No. 12 



some instances as to produce heavy infestation, but in no instance did 

 they produce infection in healthy plants. As a result of their infesta- 

 tions, however, temporary disturbances of a striking character were pro- 

 duced. Soon after these plant lice had begun to feed upon the young 

 leaves, these became more or less curled and wrinkled, and rather large, 

 conspicuous dark green spots came into evidence as a result of their 

 punctures. This spotting, which only remotely resembled the mottling 

 characteristic of the mosaic disease, was confined entirely to those leaves 

 actually attacked, and disappeared soon after the removal of the plant 

 lice from the plants. This disturbance more properly belongs to the 

 class of disturbances described by Woods ^ as stigmonose, a term which 

 he used to designate a more or less temporary and noninfectious patho- 

 logical condition produced in carnations by plant lice and other insects. 



Colonies of the common pelargonium plant louse (Macrosiphum 

 pelargonii Kalt.) were also transferred to mosaic-diseased plants and 

 subsequently to healthy tobacco plants. This plant louse did not take 

 kindly to tobacco, and colonies could not be maintained upon these plants 

 or any length of time — perhaps owing to the fact that they did not feed 

 upon the plants. Transmission of the disease was not obtained with these 

 plant lice; nor were temporary disturbances of any kind produced. 



Under field conditions the large plant louse Macrosiphum tabaci Perg. 

 appears to be an efficient carrier of the infective principle of the mosaic 

 disease of tobacco. At the Arlington Experimental Farm during certain 

 seasons this plant louse occurs in enormous numbers upon tobacco, 

 tomatoes, datura, and other solanaceous plants. During the spring and 

 summer of 191 3 this species appeared suddenly, and swarmed upon these 

 plants. Minor outbreaks have also occurred in subsequent years. There 

 is strong reason for believing that the widespread epidemic of mosaic 

 disease which affected tobacco, tomatoes, and datura during the season 

 of 1 91 3 at Arlington, Va., was associated with the presence of these plant 

 lice. In late May and early June, soon after the young tobacco plants 

 were transplanted to the field, colonies were found upon the undersides 

 of the ground leaves of practically every tobacco plant in the field. 

 These plant lice multiplied rapidly and remained upon the plants until 

 early July. After this period they disappeared so completely from the 

 plants that it was almost impossible to find a single individual in late July 

 and August. In late September, however, heavy infestations were ob- 

 served on tomato plants. 



This plant louse rarely occurs in the greenhouses at Arlington. Recent- 

 ly seedling tobacco plants have been grown in screened cages out of doors 

 and colonies of this plant louse taken from mosaic-diseased tobacco 

 plants have been confined upon them for varying periods. Under these 

 conditions successful transmission of the disease was obtained. 



•Woods, A. F. stigmonose: a disease OF carnations and other pinks. U. S. Dept. Agr. Div. 

 Veg. Physiol, and Path. Bui. 19, 30 p., 5 fig., 3 pi. 1900. 



