juiyi, I920 Transmission of Mosaic Disease of Irish Potatoes 329 



Experiment with flea beetles 



Three caged tuber units (9 hills) of the Gilbert stock were treated with 

 flea beetles {Epitrix cucumeris Harris) on June 13, 191 9, when a few 

 inches high. The middle hill of each unit was covered with a cylindrical 

 cage set inside the larger cubical one; the other two hills were treated 

 with several hundred flea beetles. These insects were collected from 

 small potato vines which developed from 100 per cent mosaic stock. 

 On June 20 the cylindrical cages were removed and most of the flea 

 beetles, which had damaged the plants considerably, were driven out of . 

 the cages or killed by hand. On June 16 two more similar tuber units 

 were treated likewise. All the hills remained healthy until dug on 

 August 27. 



As controls, four similar tuber units were treated in the same way, 

 except that the beetles were taken from plots of mostly healthy potatoes 

 or, in one unit, from bushes near the potato field. All the hills remained 

 healthy until dug on August 26. 



EXPERIMENT WITH COLORADO POTATO BEETLES 



Five caged tuber units (15 plants) of the Gilbert stock were treated 

 with Colorado potato beetles (Lepiinotarsa decemlineata Say.) on July 

 3, 1 91 9, when they reached nearly to the tops of the cages. The in- 

 sects were gathered with brush and pan from plants in all-mosaic plots 

 when from 2 days old to two-thirds full grown. Two stalks were left 

 in a hill, and the first and third hills in every cage were treated with 

 over 100 of the larvae each. These were shaken from the gathering 

 pan upon a cloth and were either rolled upon the leaves or left on the 

 cloth while it was laid on the plant. Within 24 hours the plants had 

 been damaged rather severely. They were sprayed with an arsenical 

 poison, which soon caused the death of the larvae. All the plants re- 

 mained healthy until dug on August 26 and 27. 



Three similar tuber units were treated likewise on July 7, except that 

 the larvae were obtained from plants in plots almost disease-free. These 

 also remained healthy until dug on August 27. 



FIELD OBSERVATIONS WITHOUT CAGES 



GREENHOUSE STOCKS 



Tubers from the 53 plants used in the first aphid experiment performed 

 in the greenhouse at Orono^ were planted whole. All of the 37 tubers 

 from plants which became mosaic after the introduction of aphids from 

 mosaic potatoes produced diseased hills, except 2 which came from a 

 plant with 3 out of 7 stalks apparently healthy. The 2 healthy 

 tubers were probably produced by the 3 healthy stalks. All of the 

 10 tubers from plants which remained apparently healthy until har- 

 vested, although they were fed upon by aphids from mosaic plants, were 



'ScHUiTz, H. S., Foi^OM, Donald, Hilderbrandt, F. M., and Hawkins, Lon A. op. aT. p. 35-30. 



