172 Maine Agricultural Experiment Station. 1920. 



last group, uncaged, each plant was kept in contact with a mosaic 

 plant grown in a separate pot and one became mosaic following 

 the detection of the presence of escaped aphids. 



A final experiment yielded the best results because disease- 

 free stock was used and the plants were grown during the spring 

 and summer, thus being exposed to such conditions of light and 

 heat as to enable them to maintain active growth for a longer 

 period than the plants grown previously. Ten tubers were each 

 split into four parts ; two parts produced plants which were 

 left uncaged and untreated, as checks, and two produced plants 

 that were caged until after aphids had been introduced, allowed 

 to feed, and killed by fumigation. The aphids, of the spinach 

 kind, were taken from mosaic plants, about 150 in each case. To 

 fifteen plants they were introduced by the leaf-on-stick method, 

 described above, and all these fifteen plants became mottled 

 within a few weeks. To five plants they were introduced, when 

 on the terminal vegetative buds of mosaic shoots, within an 

 open bottle laid upon the soil. This was an unfortunate method 

 since many of the aphids soon became injured or killed by com- 

 ing into contact with moisture collecting on the inside of the 

 bottle, so that only one of the five plants became mottled. The 

 20 check plants remained healthy except one which became 

 slightly mottled — the last one to do so — after uncontrolled aphids 

 had been found on it several times. 



The greenhouse experiments that have been described 

 showed that both spinach aphids and potato aphids — two species 

 of plant lice commonly found upon potato plants in Maine 13 — - 

 can transmit potato mosaic from diseased to healthy plants, and 

 that this transmission sometimes may not be followed by the 

 development of mosaic symptoms until the tubers produce the 

 second generation of plants. Since plant lice in northern Maine 

 become noticeable or numerous only during the latter part of the 

 season, it is made clear how mosaic may commonly be spread in 

 the field without the effects being apparent until the next season. 



13 Patch, Edith M. The potato plant louse. Me. Agric. Exper. Sta. 

 Bui. 147:235-257. Figs. 25-33. 1907. 



Patch, Edith M. Pink and green aphid of potato.- Me. Agric. Exper. 

 Sta. Bui. 242:205-223. Figs. 47-49. 1915. 



Also oral information has been received from the same authority 

 concerning spinach aphids. 



